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30 SOLDERLESS BREADBOARD PROJECTSBOOK 1

ALSO AVAILABLE

BP113 30 Solderless Breadboard Projects - Book 2

30 SOLDERLESS BREADBOARD PROJECTSBOOK 1

byR. A. Penfold

BERNARD BABANI (publishing) LTDTHE GRAMPIANS

SHEPHERDS BUSH ROADLONDON W6 7NF

ENGLAND

PLEASE NOTE

Although every care has been taken with the production of this book toensure that any projects, designs, modifications and/or programs etc.contained herein, operate in a correct and safe manner and also that anycomponents specified are normally available in Great Britain, thePublishers do not accept responsibility in any way for the failure, in-cluding fault in design, of any project, design, modification or programto work correctly or to cause damage to any other equipment that itmay be connected to or used in conjunction with, or in respect of anyother damage or injury that may be so caused, nor do the Publishersaccept responsibility in any way for the failure to obtain specifiedcomponents.

Notice is also given that if equipment that is still under warranty ismodified in any way or used or connected with home -built equipmentthen that warranty may be void.

© 1982 BERNARD BABANI (publishing) LTD

First Published - October 1982Reprinted - October 1988

Reprinted - May 1991

British Library Cataloguing in Publication DataPenfold, R. A.

30 solderless breadboard projects - book 1 (BP107)1. Electronic circuitsI. Title621.3815'3 TK9965

ISBN 0 85934 082 1

Printed and bound in Great Britain by Cox & Wyman Ltd, Reading

PREFACE

Although the sophistication and complexity of electronicequipment seems to continually increase, it is still possible toproduce simple and useful electronic devices that even acomplete beginner can tackle with confidence. The purpose ofthis book is simply to provide a number of designs of thiStype. A few of the designs are intended mainly to demonstratethe operation of a particular type of component or circuit, butmost have a practical application or applications.

No prior knowledge of electronic components and con-structional techniques is necessary in order to build the thirtydesigns featured here, and construction is made easier by theuse of a Verobloc breadboard as the constructional basis of allthe projects. Component layout and wiring diagrams areprovided for each project, and as the components are simplyplugged into the Verobloc, and leads to off -board components(such as controls) can be fitted with crocodile clips whichconnect to these components without, the need for anysoldering, it is a simple matter to assemble each project. It isalso an easy matter to dismantle a project and reuse the com-ponents when building a subsequent project. The circuits havebeen designed so that wherever possible components arecommon to several of the designs, and with only a modestnumber of components that are reasonably inexpensive it ispossible to build (in turn) every project featured in this book!The only tools required are a pair of wire cutters and strippers,a pair of pliers, and a small screwdriver.

It is not essential to use a Verobloc breadboard as the basisof the projects, and it should be possible to use other solder -less breadboards such as manufactured by Global SpecialtiesCorporation (GSC) or Boss Industrial Mouldings Ltd, etc.However, as the layout diagrams provided in this book arespecifically for the Verobloc breadboard it would probably beadvisable for complete beginners to use one of these, althoughmost other breadboards use a similar arrangement and readerswith some previous experience of electronics could probably

use an alternative breadboard with little or no difficulty.Please note that alternative breadboards may have differentletter and number markings to those shown in this book forVerobloc.

Solderless breadboards are not usually used as the basis forpermanent projects, but once the reader has gained somepractical experience by breadboarding some of the projects, heor she should have little difficulty in building the projects onstripboard or using some other conventional constructionalmethod.

The components employed in the designs in this book arevirtually all quite common types that are much used in home -constructor designs, and any "left-overs" should prove usefulas a stock of components for future use. Similarly, the bread-board should be useful for experimenting with simple designsother than those featured in this book, and is likely to receivemany years of heavy use.

R. A. Penfold

CONTENTS

PageCHAPTER 1: Using a Breadboard 1

Components 7Resistors 7

Capacitors 9Semiconductors 12Integrated Circuits 13

Diodes 14Potentiometers 16Photocell 17Ferrite Aerial 17Switches 18Loudspeaker 19

CHAPTER 2:Project 1 -Project 2 -Project 3 -Project 4 -Project 5 -Project 6 -Project 7 -Project 8 -Project 9 -Project 10Project 11Project 12Project 13Project 14Project 15Project 16Project 17Project 18Project 19Project 20Project 21

The Projects 21Simple Audio Power Amplifier 23Telephone Amplifier 28Light -Activated Switch 34Dark -Activated Switch 38Light Alarm 41Dark -Activated Alarm 45Light Change Switch 48One -Second Timer 53Metronome 57

- "Heads" Or "Tails" 61- 4-60 Second Timer 66- Audio -Alarm Timer 70- Simple Oscillator 75- Loudspeaker Oscillator 79- Tone Generator 83- Warbling Doorbuzzer 86- Two -Tone Train Horn- Falling -Tone Version 94- Simple Touch -Switch 97- Touch Switch 101- Transistor Checker 105

PageProject 22 - Reaction Game 110Project 23 - Sound -Activated Switch 114Project 24 - Slide Timer 119Project 25 - Moisture Detector 123Project 26 - Water -Activated Alarm 127Project.27 - Crystal Set 131Project 28 - Personal MW Radio 136Project 29 - MW Radio 141Project 30 - Fuzz Unit 145

CHAPTER 1

USING A BREADBOARD

The term "breadboard" is one that is likely to be a littleconfusing to beginners, but it simply means a board on whichelectronic circuits can be built and tested. Modern breadboardsare almost invariably of the solderless type, where componentsare simply plugged in and unplugged as desired. Apart fromthe obvious advantage of enabling circuit changes to be rapidlymade when experimenting, it also enables components to bereused almost indefinitely. Components will in fact eventuallywear out because the leadout wires will need to be reformedslightly to fit into new layouts, and the leadout wireseventually suffer from metal fatigue and break off (usuallyclose to the body of the component so that it becomes useless).This can be overcome though by only using components forbreadboarding for a limited period of time, and then usingthem in finished projects and getting a new stock of bread-boarding components.

Although the term "breadboard" may seem inexplicable,it is probably derived from the early days of electronics whenvalved circuits were normally prototyped on a large woodenboard (like a breadboard) into which nails were hammered.Components were then connected to the nails, and additionalwires were used to connect the components in the desiredfashion. Some finished equipment actually used this methodof construction. A variation on this type of board was to usescrew terminals so that no soldering was necessary; the originalsolderless breadb9ards, in fact!

Modern breadboards are much simpler and easier to use,and apart from being useful to experienced electronic engineersworking on prototype designs, they also have attractions forbeginners. One is simply that they are very easy to use, andanyone can plug in and remove components from a solderlessbreadboard; no previous experience of electronics constructionbeing necessary. When the inevitable mistakes in the

component layout do occur, it is an easy matter to checkthrough the layout and remedy the errors since no awkwarddesoldering is necessary. It is also easy to quickly build andexperiment with a number of projects at low cost with every-thing involved being reusable, including the breadboard.

The breadboard used by the author when constructing theprojects featured in this book was a Verobloc, and the com-ponent layouts provided are for this particular breadboard.The Verobloc uses the arrangement shown in Figure 1.

1 6S00--111,-111-11-111.411A BCDEF GHJKL M

11-6-0-411..411 --11-41-41* -111-11-111.41 I 11* -41-6-41-4111

*-1*-111-111-111

111 -11 -1* -0-411111-111-116-11-11

11-111-11-41-111 111-0-11-111-*7 ii -e---

0-10-0-46-11. 11-11-11-10-11

ID -11-11-111-111111-0-#-411 11-45-11111111-6

111-1041-41-111 111-0-e-111-1111 3 is-a---a-e --s-a- 13

F -1111 -1* -11111 0-11641-41.-.-.-.-. 111 -1* -1111,-411-111

10-1111-41-11- 1111 -1, -*-111-11

111-41-0-11-11 21-41-6-0-1111* -0-111-111.-41 11-111-0-11-.19 --e-aas

111-11-0-11-.111-111-1FiFil -411-1111-6-111111-11-111-0-111 111-41-641--1110-4F11-411-111 1* -11-111-11-11125.E+.. i s-a-erii 2511-41-11-41-4 11,0-11-111.* -11-111-6- 10-11-16-11-0111-11-0-11-11 11 -111/ -11 -1* -11

c 11111-41-111-111 1118-11-111.-1116-111-0-1101 1* -111 -0 -11* -111

A BCDEF GHJKL M31 11F-1111-11H--.11-F11-11--U 31

Fig. 1 The general arrangement of the Verobloc

2

Numbers are used to identify the horizontal rows of holes andletters are employed to identify the vertical rows of holes. Inorder, to make it easier to copy component layouts the identi-fication letters and some of the numbers are marked on thelayout diagrams and on the Verobloc itself.

In Figure 1 lines are used between holes to show how theyare internally interconnected and, for example, all the holes inrow ''A" are connected together. The rows of holes around theperiphery of the board are mainly used to carry the twosupply lines. The spacing of the holes is such that mostintegrated circuits can be plugged straight into the boardwithout the need for any special adaptors, and this is certainlythe case with the two integrated circuits used in the designsdescribed in this publication. Each hole in the board is fittedwith a spring terminal which will readily accept any componentleadout wire or pin.

Controls and some other components do not plug straightinto the board, but are mounted off -board on a mountingbracket of some kind, and connected to the board via singlecore insulated leads. Multistrand wire is normally used forinterconnecting wires of this type, but multistrand wire can bedifficult to connect to a solderless breadboard as the strandstend to splay as the wire is pushed into the board. If you havesoldering equipment this can be overcome by tinning the endsof multistrand leads with solder, but it is otherwise better touse single strand wire. Any PVC -covered type that is notunusually thick or thin should be suitable (i.e. about 22 SWG).

A panel on which the controls can be mounted, and whichwill slot into the Verobloc can be obtained, but there is aslight problem in using this with some of the designs featuredin this book because some of the control components are quitelarge and would obstruct the board. One way around this is touse two Veroblocs (they can be plugged together either side -by -side or end -to -end), one simply being used to space thecontrols away from the board that is used to carry the othercomponents. Although the second Verobloc is not needed forthe designs described in this book, it will almost certainly beput to use as you progress to more complex projects. Analternative method is to mount the Verobloc on a plywood or

3

hardboard base fitted with an aluminium front panel on whichthe controls are mounted. The battery (all the designs use aPP6 9 -volt type) can also be mounted on the baseboard using asimple mounting bracket fabricated from aluminium. Figure 2gives details of a suitable general arrangement for the unit, butobviously any sensible layout can be employed. The potentio-

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meters and variable capacitor used in the circuits in this bookneed standard 10 mm diameter mounting holes. If the push-button switch used is of the usual inexpensive miniature type

it will require a 7 mm diameter mounting hole. Most miniaturetoggle switches require a 6.4 mm (V4 in) diameter mountinghole, but some types require a smaller mounting hole of5.2 mm (0.2 in) in diameter. It is advisable to check this bymeasuring the mounting -bush diameter of the particular com-ponent being used prior to drilling the mounting hole.

Although the Verobloc breadboard is solderless, thecontrols are not and have tags or pins which are only intendedto take wires via soldered joints. Ideally single -strand insulatedleads about 150 mm or so long should be soldered to the tagsor pins of the controls, and about 5 mm of insulation shouldbe removed from the free end of each lead to facilitateconnection to the Verobloc breadboard. Fortunately there isan alternative method of connecting leads to the controls andthis is simply to use crocodile clips. They have two smalljaws which are pushed closed by a built-in spring, and the jaws

are simply clipped over the appropriate tag or pin. With mostcrocodile clips it is not necessary to solder the leads to theclip, and there is either a screw which can be used to clamp thelead in place, or a couple of metal lugs which can be presseddown onto the lead using a pair of pliers and thus firmly fix itin place. In this application the best type of crocodile clip touse is probably one of the very small types having a PVCcover. These will clip onto the tags of potentiometers withoutovercrowding, and the PVC covers insulate the clips from one

another so that accidental short circuits are avoided.A few of the circuits use a telephone pick-up coil or a crystal

earpiece, and these are both fitted with 3.5 mm jack plugs.One way of making the connections to these is to fit a 3.5 mmjack socket on the front panel of the breadboard unit, andthen connect this to the board using crocodile clip leads in thesame way that connections are made to the controls. Of course,the pick-up coil or earphone plug is plugged into the jacksocket. An alternative method is simply to use a couple ofcrocodile clip leads to make the connections directly to theplug.

5

The connections to the battery are made via a battery clipof the appropriate type, and a PP6-size battery uses the sametype of connector as the popular PP3 battery (and this type ofconnector is normally sold as a PP3 type even though it isactually used for other types of battery). The leads attachedto the battery connector are almost certain to be of the multi -strand type, and as mentioned earlier, will not easily plug intoa solderless breadboard. If it is not possible to tin the leadswith solder so that the strands of wire are held together,simply twisting the strands of wire tightly together might besatisfactory. Another possibility is to fit the two leads withcrocodile clips which can be clipped to a couple of pieces ofsingle -strand wire (one clip to each piece of wire), and thesetwo wires are then plugged into the breadboard.

Some of the projects use a loudspeaker, and this could bemounted on an aluminium panel fitted on the left-hand side ofthe breadboard assembly. Unfortunately most loudspeakers ofthe correct type do not have any built-in means of panelmounting, and it will either be necessary to glue the speaker inplace, or some simple method of clamping it in place must bedevised. If it is glued in place, use a good -quality adhesive suchas a clear type or an epoxy one, otherwise in use it is likelythat the speaker will simply come unstuck. Be careful to applythe adhesive only to the front outer rim of the speaker, andnot onto the diaphragm (which could severely reduce thequality of the speaker). If this method of mounting is used itshould be borne in mind that it will be difficult to remove thespeaker for use elsewhere without at least slightly damaging it,although if it is carefully cut free it will almost certainly befound to be perfectly usable.

For experimental purposes it is not essential to have thespeaker properly mounted at all, and it can simply be laid facedownwards to one side of the breadboard assembly, preferablyon a magazine or a few sheets of cardboard. This should providean output of reasonable quality, although a small loudspeakergives no significant bass response even if placed in a properenclosure. Of course, the speaker can be fitted into a smallcabinet if desired, and this will give optimum quality andvolume.

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The two connections to the loudspeaker can be made viaa couple of crocodile clip leads, as for the other off -boardcomponents.

ComponentsThe main problem for someone starting electronics as a hobbyis simply that of identifying the various components used inprojects. Before proceeding to the projects a brief descriptionof the components used in them will be given so that even acomplete beginner should have no difficulty in sorting outwhich component is which, and connecting each componentinto circuit correctly.

ResistorsThese are small cylindrical components having a leadoutprotruding from each end. The value is not marked in numbersand letters, but is indicatpd by four coloured bands aroundthe body of the component. The value is in units called"ohms", and resistors often have values of many thousands ofohm's, or even a few million ohms. In order to avoid constantlyusing very large numbers it is common for resistance to bespecified in kilohms (k) and megohms (M). These are equal toa thousand ohms and a million ohms respectively. Thus aresistor having a value of 33,000 ohms would normally be saidto have a value of 33 k, and a resistor having a value of2,700,000 ohms would normally have its value given as 2.7 M.It is common these days for the units symbol to be used toindicate the decimal point as well. This sometimes furthershortens a value in its written form, and there is no danger ofa decimal point being overlooked due to poor quality printingor something of this nature. In our two examples given abovethe value of 33 k would not be altered since the "k" alreadyindicates the position of the decimal point, but 2.7 M wouldbe altered to 2M7.

The resistor colour code is very straightforward, with thefirst two bands giving the first two digits of the value, the thirdband giving a multiplier (i.e. the first two digits are multipliedby this third figure in order to give the value of the componentin ohms), and the fourth band showing the tolerance of the

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component. The resistor colour code is detailed below.

Colour Istl2nd Band 3rd Band 4th BandGold not used 0.1 5%Black 0 0 not usedBrown 1 10 1%Red 2 100 2%Orange 3 1,000 not usedYellow 4 10,000 not usedGreen 5 100,000 not usedBlue 6 1,000,000 not usedViolet 7 not used not usedGrey 8 not used not usedWhite 9 not used not usedSilver not used 0.01 10%No Band not used not used 20%

Thus, in the example shown in Figure 3 the first two digitsof the value are 4 (yellow) and 7 (violet), giving 47 which mustbe multiplied by 100 (red), giving a value of 4,700 ohms. Thiswould normally be written at 4.7 k or 4k7. The fourth band isgold which indicates that the value of the component is within

1 st bond ( yellow)

2nd bond (violet)r3rd bond (red)

i--4th band (gold)

1111

smol I gap H F.-4 large gap

47 X 100 = 4700 ohms, 4.7 k, or 4k7.Tolerance is 5%.

Fig. 3 Resistors have their value marked using a colourcode

8

5% of its marked value. Note that it is perfectly all right to usea component having a closer tolerance than is specified in acomponents list (a 2% type can be used in place of a 5% typefor example), but a component having a higher tolerance thanthat specified (such as a 10% type instead of a 5% type) is notacceptable.

Resistors also have a power rating, and this is not usuallymarked on the component (except in the case of high powertypes where the value and wattage may both be written on thecomponent, no colour codes being used). For the circuits inthis book ordinary miniature 1/8, 1/4, or 1/3 watt resistorsare satisfactory since the power levels involved are very low.Higher power resistors are not really suitable, and this is dueto their physical rather than electrical characteristics. Higherwattage resistors are physically quite large and would bedifficult to fit into the available space, and some have verythick leadout wires which will not fit easily into solderlessbreadboards.

Incidentally, in order to aid the selection of a resistor of thecorrect value, all components lists in this book have the colourcode for each resistor alongside the value. Thus, even if you donot understand the resistor colour -coding system you shouldstill be able to pick out the appropriate resistors with the aidof the components lists.

CapacitorsMost capacitors used to look much the same as resistors butwere normally a little larger and had the value written on theirbody rather than marked using a colour code. Moderncapacitors are still generally somewhat larger than resistors,but they often have both leadout wires coming from the sameend of the component as this makes them more conJenient foruse with printed circuit boards. Also, they often have rect-angular rather than tubular bodies.

The projects featured in this book use several types ofcapacitor, including electrolytic types. These are available asaxial (with the leadout wires coming from opposite ends of thecomponent) and printed circuit types. Axial electrolytics wereused when developing the projects, and the layout drawings

9

show the electrolytics as axial components, but printed circuitmounting types can be fitted into the layouts with nodifficulty.

An important point to bear in mind with electrolyticcapacitors is that they are polarised, and must be connectedto the circuit the right way round (resistors, and most othertypes of capacitor can be connected either way round). In thecomponent layouts given in this book the leadout wires areidentified by "+" and "-" signs, and the leadout wires of theactual components are identified "+" and "-" signs on thebodies of the components. Additionally, axial types usuallyhave an indentation around one end of the component's body,and this indicates the end of the component from which thepositive (+) leadout wire emerges.

One of the capacitors used in a few projects is a tantalumbead type, and like an electrolytic capacitor this is a polarisedcomponent. Tantalum capacitors are normally small, bead -shaped components (which are sometimes called tantalumbead capacitors) which have both leadout wires coming fromthe same end of the body. The positive leadout wire should beidentified by the appropriate sign marked on the body of thecomponent. Be careful to connect the tantalum capacitor theright way round as capacitors of this type are easily damagedby a voltage of the wrong polarity.

Another type of capacitor used in the projects is a ceramicplate or disc ceramic type. Either type is suitable, and the onlyphysical difference between the two is that the plate type isrectangular while the disc type is obviously circular. Capacitorsof this type sometimes have the value written on the body ofthe component in a straightforward manner, but it is notunusual for the value to be marked using less than obviousfigures. For example, the value might be given as 332, toindicate a value of 3.3 nF. The first two numbers give the firsttwo digits of the value, and the third number indicates thenumber of zeros to be added to give the value in picofarads.Thus 332 indicates a value of 3,300 pF, and as 1,000 pFequals one nanofarad (1 nF), 3,300 pF equals 3.3 nF. Inci-dentally, larger capacitance values are usually given in micro -farads (µF); 1µF being equal to 1,000 nF or 1,000,000 pF.

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The other fixed -value capacitors used in the projects are ofthe polyester variety, and the Mullard C280 type (or anysimilar type) will fit into the component lay outs most readily.These are rectangular, printed -circuit -mounting capacitors, andare unusual in that the value is marked using a colour code.There are five coloured bands around the component, asshown in Figure 4, and the first three give the value of thecomponent in the same way as the resistor colour code. How-ever, the value is in picofarads rather than ohms. The last twobands show the tolerance and maximum working voltage ofthe component respectively. For the values used in theprojects described in this book the last two bands will pro-bably be black (20% tolerance) and red (250 volts DCmaximum), but other colours are sometimes encountered.,such as white (10%) and yellow (400 volts DC maximum).This is of no consequence, and any C280 polyester capacitorsare suitable for use in these projects.

Where polyester components are specified in a componentslist, the appropriate colour code is given to aid the selection ofthe correct component.

The radio circuits use a variable capacitor, and this is in factthe tuning control. The specified type is a solid dielectric

111111111111111111111111111111111111

Bond 1 (e.g. brown)

TBond 2 (e.g. block)Bond 3 (e.g. yellow)

r Band 4 (e.g. block)Bond 5 (e.g. red)

100,000 pF (100 nF or 01 µF),20%, 250 V max.

Fig. 4 C280 series polyester capacitors, like resistors, usecolour coding

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component having a maximum capacitance of 300 pF, but anyvariable capacitor having a maximum value of about 200 pF to300 pF is suitable from the electrical point of view. However,the specified "Dilecon" component manufactured by JacksonBrothers Ltd (and available from a number of the larger com-ponent retailers) has a standard 10 mm mounting bush and6.4 mm (1/4 in) spindle. Beware of cheaper types having mount-ing arrangements and (or) non-standard spindle sizes whichwould make them difficult to use.

SemiconductorsSeveral types of semicondutors are used in the projects, andwe will start with the two transistors. Transistors have threeleadout wires which are called the base, emitter, and collector.It is essential that these are connected correctly, as there is nochance of a project working if they are not. Fortunatelymodern transistors are not easily damaged, and incorrectconnection is not likely to damage a device (or other compo-nents in the circuit). Only two types are used in the projects,and these both have the same case and leadout configuration(see Figure 5). An important point to note here is thattransistor leadout diagrams show the base view of the device.In other words, it is shown as it is seen if the leadout wires aretowards the viewer. In the component layout diagrams thereis insufficient space for the leadout wires to be identified bythe full words "base, "emitter", and "collector", and these

Fig. 5 Leadout details of the BC109C and BC179 devices

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are therefore abbreviated to "b", "e", and "c" respectively.

Integrated CircuitsIntegrated circuits have a wide variety of packages, but herewe are only concerned with two types of integrated circuit,the TLO81CP operational amplifier and the LM380N audiopower amplifier. The TL081CP haS an 8 -pin DIL (dual in line)plastic package, and the LM380N has a 14 -pin DIL plasticpackage. As can be seen from the pinout diagram of Figure 6,the two packages are essentially the same; the 14 -pin versionsimply being an extended version of the 8 -pin one. Note thatintegrated circuit pinout diagrams are top views, and not baseviews like transistor leadout diagrams. In other words, thedevice is pictured looking at the side that carries the typenumber and with the pins pointing away from the viewer.

The only point to watch when connecting one of the inte-grated circuits is to make sure that it is not plugged in upside-down. Check that the indentation on the top of the packageand at one end of the device corresponds properly with thecomponent layout diagram (where this indentation will alwaysbe clearly shown).

There are alternative operational amplifier integrated

Fig. 6 Pinout details of the TL081CP and LM380N devices

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circuits that can be used instead of the TL081CP deviceincidentally, but only internally compensated BIFET types aresuitable, and the standard 741C operational amplifier is notsuitable as it will not function properly in some of theprojects. Alternative operational amplifier integrated circuitsthat are suitable are the LF351 and TLO71CP devices.Although some FET operational amplifier devices requirespecial handling precautions, these are the types which haveMOSFET input stages, and not the BIFET devices mentionedabove which can be handled like any normal semiconductorcomponent without risk of damage. Note that there are nocommon alternatives to the LM380N device and that the 14 -pin version of this device must be used (a few suppliers alsooffer an 8 -pin version).

DiodesTwo types of ordinary diode are used in the projects, the0A90 germanium type and the 1N4148 silicon type. Physic-ally these are very much the same, the 0A90 type being some-what larger than the 1N4148 device. The main point to noteabout diodes is that they are polarised components and mustbe connected into circuit the right way round if the circuit isto function properly. The cathode (+) lead of a diode isnormally marked by a band around the appropriate end of thecomponent's body, and this band is shown on the componentlayout diagrams in order to indicate diode polarity.

One minor complication is that there are a few diodesaround which for no obvious reason, have the band markedaround the wrong end of the component! Therefore, if acircuit which uses diodes fails to work it would be advisable tocheck the diodes with some sort of component tester if thisis possible. Another minor complication is that some diodeshave a number of bands marked around their body, and insuch cases the manufacturer uses these bands to indicate thediode type number rather than simply marking the typenumber on the component. In such cases the bands arenormally offset towards the end of the component from whichthe cathode (+) leadout wire emanates. Figure 7 should helpto clarify this point.

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m )Fig. 7 Diode polarity is shown by a band (or bands) on

the component

Two light -emitting diodes (LEDs) are employed in theprojects, and these are both small types (3 mm or 0.125 in),but the TIL209 is a red device and the TIL211 is a green LED.Many component suppliers do not use type numbers for LEDsand simply describe them as a LED of a certain colour,diameter and shape (the TIL209 and TIL 211 are both roundtypes incidentally). With most LED circuits, including thosedescribed here, from the electrical viewpoint the size, colour,and shape of the LED is not important, and with the excep-tions of a few special types such as infra -red and multicolourtypes any LEDs can be used. For the circuits that use bothLEDs it is not even essential to use LEDs of different colours,but a two-colour display will probably be clearer than onehaving LEDs of the same colour.

There are various ways used to show which LED leadoutwire is the anode and which is the cathode, one of the mostcommon being to have one leadout wire shorter than the otheras shown in Figure 8. Usually the shorter leadout wire is thecathode one (+), but unfortunately this is not always the case,and sometimes a different method of identification is used.With some LEDs there is no obvious way of telling which lead -out wire is which as they seem to be symmetrical! If themanufacturer's or retailer's data is not available, or does notmake it clear which leadout wire is which, you can simply tryeach LED either way round. If a device is wrongly connected

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LED

Fig. 8 A common way of showing LED polarity is to haveone leadout (usually the cathode) shorter than theother

it will fail to light but is unlikely to sustain any damage, and itwill merely be necessary to reverse the polarity of the devicein order to make the circuit function correctly.

PotentiometersThese are available in a number of different types, but thecircuits in this book require the common carbcn type that areavailable from virtually any electronic component retailer.Wire -wound types are electrically suitable, but are often physic-ally rather large and more expensive and are not recommended.Rotary types are preferable to slider types as the latter areusually much more difficult to mount, and all the componentlayout diagrams in this book which show a potentiometerassume that a rotary type is used. In these diagrams the poten-tiometer is shown viewed from the rear (i.e. looking from theopposite side to the spindle and control knob). It is importantto connect the potentiometer correctly in most cases as other-wise, for example, advancing a volume control might give adecrease in volume rather than an increase.

Potentiometers are available with a linear law (lin. = linearabbreviated types) or with a logarithmic law (log. types), andcircuits will work if the wrong type is used (provided it has theright value of course). However, if we take a volume control asa simple example, a logarithmic type would normally beutilized in this application, and using this type of potentio-meter gives an apparently smooth and easily controlledincrease in volume as the control is advanced. If a linear type is

16

used there is an apparent sudden increase in volume as thecontrol is advanced from zero, with very little apparent changein volume over the major part of the control's adjustmentrange. It is possible to set the volume at any desired level, butthe volume -level is comparatively difficult to control accurately.Thus it is advisable to use a potentiometer of the typespecified in the appropriate components list.

PhotocellThe photocell used in the light -activated circuits is an RPY58Awhich is a small cadmium sulphide photo -resistor, andphysically is flat, about 5 mm square, and has the two leadoutwires coming from one edge. It looks very much like a smallceramic plate capacitor, in fact.

Like an ordinary resistor, a cadmium sulphide photocell isnot a polarised component and can be connected into circuiteither way round. The light-sensitive surface of the componentis the one having a gold patterned surface, and not the one towhich the two leadout wires can be clearly seen to connect.

Ferrite AerialThe radio receiver projects use a medium -wave ferrite aerial,and a suitable type is the Denco MW5FR. Like all ferriteaerials, this consists of a coil (or coils) of wire on a piece offerrite. In the case of the MW5FR the piece of ferrite is a rodmeasuring about 127 mm x 9.5 mm and there are two coils ofwire on a paper former which is slipped onto the rod. The twocoils are a large (tuned) winding and a smaller (coupling)winding. They are wound using wires of different colours sothat it is easy to determine which leadouts come from whichwinding. The coils are wound using Litz wire (a number ofthin enamelled copper wires twisted together and given anoverall layer of insulation as well), and the ends of the leadoutwires are ready -tinned with solder so that they should fit intothe breadboard without too much difficulty.

It is not essential to use the Denco aerial, and the circuitshave also been tested using an Ambit MWC2 aerial coil on anAmbit 140 mm X 9.5 mm ferrite rod. However, this aerial coilhas tag connections rather than leadout wires, and leads must

17

either be soldered to the tags or connected using smallcrocodile clips. The circuits should work properly using anyother standard medium -wave ferrite aerial provided the aerialcoil has the small coupling winding.

The ferrite aerial can simply be layed on the workbench,or at the rear of the breadboard assembly if a unit along thelines of Figure 2 is constructed. Alternatively, the aerial can bemounted on the breadboard assembly using either a "P' stylecable grip capable of taking a 9.5 mm diameter cable (orferrite rod in this case, of course), or special mounting clipswhich are available from Ambit International. If the aerial isleft loose, bear in mind that ferrite is a very hard and brittlematerial, and that if the aerial is dropped it is quite likely thatthe ferrite rod will break. Also bear in mind that the aerial willnot operate properly if it is laid on a metal surface and thatsome plastic laminates used for bench and table tops have alayer of metal foil on their underside.

SwitchesOnly two types of switches are used in the projects, and thereis little chance of confusion since one is a push-button typeand the other is a miniature toggle switch (i.e. it is operated viaa small lever). The push-button switch must be a push -to -maketype and not a push -to -break type, and it must not be alatching type. In other words, the two tags are connectedtogether when the switch is operated, and disconnected whenthe push button is released. There should be no problem inobtaining a switch of the correct type as these are the mostcommon and cheapest type of push-button switch. Although aminiature toggle switch was used when testing the prototypeprojects, a standard size toggle switch is also suitable, but amuch larger mounting hole will be required (usually about13 mm or ih in in diameter). In the components list the toggleswitch is specified as an SPST type, and this means a single -pole, single -throw type. In other words, it is just a simpleon/off type switch, and switches of this type are sometimesadvertised as on/off switches rather than SPST types.

Some of the projects use a relay, and this is a switch that isoperated via an electromagnet, and is not operated manually.

18

The circuits can use any relay having an operating coil with aresistance of about 185 ohms or more, and capable of operatingfrom a 9 volt supply. A type having a fairly high coil resistancehas the advantage of a comparatively low battery currentdrain, and thus gives longer battery life. Most relays operatetwo or four sets of switch contacts, and these are often of thechangeover type rather than simple on/off contacts. A relayof this type is perfectly suitable even if you merely want therelay to switch a single piece of equipment on and off. How-ever, make sure that the voltage and current ratings of therelay are sufficient to control the piece of equipmentconcerned. Relays do not normally have leadout wires, and thetags of the relay must be connected to the breadboard viasuitable soldered or crocodile clip leads.

LoudspeakerThere should be no difficulty in identifying the loudspeakerwhich will have a diaphragm made from a paper -like substance,and about 50 to 75 mm in diameter (depending on what sizeloudspeaker you purchase). Apart from the diameter of theloudspeaker, advertisements will also quote an impedance inohms. The size of the loudspeaker is not of great importancein this case and any miniature type will do, but it is importantto use a type having the correct impedance. All the designsrequire a high -impedance loudspeaker, and any impedance inthe range 40 to 80 ohms is suitable. A somewhat higher impe-dance would be satisfactory, but loudspeakers having animpedance of more than 80 ohms do not seem to be available.Except where noted otherwise, the use of a low -impedanceloudspeaker such as an 8 -ohm type is not recommended.

Loudspeakers should be treated carefully since thediaphragm is easily damaged, and you should always hold aloudspeaker by the magnet housing at the rear of the com-ponent.

19

CHAPTER 2

THE PROJECTS

In this chapter details of the thirty projects will be provided,and the following will be given for each project:

- Introduction to the project and its applications;- Circuit description;- Circuit diagram;- Component layout diagram;- Components list;- Notes on use of project and construction tips.

It is likely that the circuit diagram and circuit descriptionwill be of little interest to the complete beginner who will beunfamiliar with even the simplest of electronics theory. How-ever, at some later date, when some theory of electroniccomponents has been learnt, one can always return to thesedescriptions and diagrams, and perhaps rebuild the circuits aswell. For anyone interested in the theory of electronics anumber of breadboard projects and circuit descriptions are anideal way of testing the theory in practice, and in a way thatprovides fun and enjoyment.

Detailed notes on how to construct the projects on thebreadboard will not be given since the layout diagrams arelargely self-explanatory, and this would also be largely justreiterating points from the previous chapter. There are just oneor two further points which should be kept in mind whenbreadboarding the projects.

It is not necessary to plug in the components in any specialorder, but it is best to start with the link wires, transistors,and integrated circuits, and then add the resistors, and otherpassive components. and finally connect the battery controls,loudspeaker, etc. The link wires are simply short pieces ofsingle -strand wire, and can be pieces of the same wire that isused to wire the breadboard to the controls. There is no needto trim the leadout wires of components to length, and it is in

21

fact unwise to do so as this might result in a component havingleadout wires that are too short to enable it to fit into a subse-quent component layout. However, if the leadout wires areleft full-length be careful to avoid accidental short circuits.When removing an integrated circuit from the board use asmall screwdriver (or a proper integrated circuit removal tool)to gently prise the device clear of the breadboard. It is quitelikely that if the device is removed by hand one end will pullclear of the board while the other is still in place, and thiscould result in some of the pins breaking off.

Where necessary, any special setting -up is described in detail,and any special points concerning the construction of theproject as a finished and cased unit will be explained.

22

Project 1 - Simple Audio Power AmplifierThis extremely simple circuit (see Figure 9) provides an out-put of power of about 200 mW RMS (about equal in volumeto a small or medium -size transistor radio) and has an inputsensitivity of about 50 mV RMS into 100 k for maximum out-put. This enables the unit to be fed from a variety of signalsources, such as a crystal or ceramic pick-up, radio tuner, etc.The circuit is primarily intended as a simple one to demon-strate the properties of the LM380N audio -power amplifierdevice, and it also makes a very useful and inexpensive work-shop amplifier if the circuit is built as a proper, cased project.

The LM380N has been a very popular device since it firstbecame available to the home -constructor, and the reasons forthis are its good quality output, and the very small number ofdiscrete components needed to turn it into a practical audioamplifier. As we shall see later, it is also a very versatile devicethat can be used in applications other than audio amplifierones.

VR1 is the volume control, and the internal circuitry of theLM380N is such that no DC blocking capacitor is neededbetween the slider of VR1 and the intput of the LM380N(IC1). A DC blocking capacitor is used at the input to VR1though, so that any DC component that might be present onthe input signal is blocked from the input of ICI. IC1 has aninternal bias circuit that gives a quiescent output voltage at theoutput terminal (pin 8) of nominally half the supply voltage.The AC input signal causes the output to swing positive andnegative of this quiescent level by about plus and minus 3 voltsor so, and this enables a reasonably high output power to beobtained without the output going fully positive or fullynegative, and serious distortion being caused by clipping of theoutput waveform. If a DC component on the input signal wasallowed to reach the input of ICI this would alter thequiescent output voltage of IC1, and could resillt in the outputgoing almost fully positive or negative. Only a very small out-put power would then be possible without the signal becomingbadly distorted. Cl provides DC blocking at the output so thatthe loudspeaker only receives the varying output voltage fromICI, and not the quiescent (DC) output voltage which would

23

give a high standing current through the loudspeaker andproduce a very high level of current consumption.

The LM380N has a class AB output stage, and this meansthat the average current consumption of the device (which isaround 10 mA) remains virtually constant at low and mediumoutput powers, but increases somewhat at high output powers.This gives reasonable battery economy, and a PP6 or larger 9volt battery makes a suitable power source. There is somevariation in the supply voltage due to variations in the loadingon the battery by IC1 as the output power inevitably fluctuatesquite rapidly and over a fairly wide range with any practicalinput signal. This can result in a loss of performance orinstability, and decoupling capacitors C2 and C3 are includedto prevent either of these occuring. An additional decouplingcapacitor can be added from pin 1 of IC1 to the negativesupply, and this decouples the supply to the preamplifierstages of the device. This is not normally necessary when theLM380N is employed with a battery supply, and is a facility

Fig. 9 The circuit diagram of the Simple Audio Amplifier

24

LS1

Fig. 10 Constructional details of the Simp e AudioAmplifier

25

that is normally only required when the device is used with amains power supply that has a high ripple content. Such acapacitor is not used in any of the circuits in this book thatutilize the LM380N device.

Some readers might be confused by the fact that one leadto IC1 in Figure 9 is marked "3, 4, 5, 10, 11, 12". This lead ismarked with six pin numbers merely because these six pinsare internally interconnected, and a connection to one ofthem is also a connection to the other five.

The Verobloc component layout for the Audio PowerAmplifier is given in Figure 10, and this is so simple that thereis very little that can go wrong (remember to fit IC1, Cl andC3 round the right way though).

If the unit is built as a cased project the input leads fromthe component board should be connected to a two-way audiosocket such as a standard or 3.5 mm jack type. The caseshould ideally be an all -metal type so that it screens thecircuitry from stray pick-up of mains hum and similarelectrical signals, and the case should be earthed to thenegative supply. With most types of audio socket this chassisconnection will be automatically provided through the earthlead to the socket. The test leads should use screened cable(the outer braiding connecting to the chassis of the amplifier).

A simple way of testing the breadboard version of theamplifier is to connect a crystal earphone to the input of thecircuit. The earphone can then be used in reverse as a sort ofcrude microphone, although it will only give a fairly lowoutput level and the volume obtained will not be very high.Also, as the earphone lead is not a screened type it is likelythat a fair amount of mains hum and other stray pick-up willbe evident at the output.

An interesting feature of the LM380N device is that it hastwo inputs, pin 2 is the non -inverting input and pin 6 is theinverting input. An input signal to'pin 6 produces a change inoutput voltage that is of the opposite polarity, whereas aninput to pin 2 gives a change in output voltage that is of thesame polarity as the input signal. There is no audibledifference between the two, and the fact that the signal isinverted through IC1 if the input at pin 6 is used is not really

26

of any practical importance. The circuit works equally wellwhichever of the two inputs is used, and this fact can easilybe demonstrated in practice. To do so you can try pluggingthe lead from the slider (centre tag) of VR1 to hole B-23so that it connects to pin 6 of IC1 and the unit will appear tooperate as before. If a link is used to connect hole D-19 tohole D-23 so that both inputs are used, they will tend tocancel out one another and give very little voltage gain!

Components for Project 1 - Simple Audio -Power Amplifier(Fig. 9)

Resistors:VR1 100 k log. carbon

Capacitors:Cl 100 /If 10 V electrolyticC2 100 nF polyester (brown, black, yellow, black, red)C3 100µF 10 V electrolyticC4 220 nF polyester (red, red, yellow, black, red)

Semiconductor:IC1 LM380N

Switch:S1 SPST miniature toggle type

Battery:B1 PP6 size 9 volt and connector to suit

Loudspeaker:LS1 Miniature type having an impedance in the range 40 to

80 ohmsMiscellaneous:

VeroblocControl knobWire

27

Project 2 - Telephone AmplifierThis is a simple device which can be used to boost the outputof a telephone to loudspeaker volume so that a number ofpeople can follow a telephone conversation, and no directconnection to the telephone is needed. The audio signal ispicked up using a special coil that is fitted to the base partof the telephone using a built-in rubber suction cup. In effect,the pick-up coil and a component within the telephone form a

28

(VR130D

SK1

S1

red

Batteryclip

black

A BCDEF --IGHJKL111-16-11bRitill ID -M--1111-11-11

rl 111-1211-411-111

POIe 1111

``CIS w111-1111-111-41-1111

M-111-11-111-11

10-111-11111111-11

a r

iaGE>--

19.6'

-a

,HJIKL-V- a '3

LS1

Fig. 12 Constructional details of the Telephone Amplifier

29

transformer, and give the required audio signal. The unit hasother possible applications such as an intercom or baby alarm,as explained later.

Figure 11 shows the circuit diagram of the TelephoneAmplifier and Figure 12 gives the breadboard componentlayout.

The output circuitry of the unit is basically the same as theamplifier described in the previous section of this book. Theonly difference is the addition of a capacitor (C3) from theinput of IC1 to the negative supply rail. The purpose of thiscapacitor is to reduce the upper audio response of the circuit,and this gives an improved signal to noise ratio (i.e. less back-ground "hiss") without reducing intelligibility.

The voltage gain of the LM380N device is set by an internalnegative feedback network at approximately 34 dB (50 times),and this is inadequate to give a reasonably loud output sincethe pick-up coil provides only a very small signal level. A high -gain common -emitter amplifier based on Tr 1 is therefore usedto boost the gain to a suitably high level, and the voltage gainof Tr I is in the region of 40 dB (100 times). This stage uses aconventional configuration with R2 as the collector loadresistor and R1 biasing the circuit. Cl provides DC blocking atthe input, and is necessary as the pick-up coil has a low DCresistance and would otherwise virtually short-circuit the baseterminal of Trl to the negative supply rail.

The input signal is inverted through Tr 1 , but not throughIC1 so that the input and output of the amplifier are out -of -phase. Stray feedback at high frequencies is unlikely to causeinstability therefore, despite the very high gain of the circuit,since such feedback will be of the negative variety.

If you decide to build this one as a permanent project itwould be advisable to use a metal case so that the sensitiveinput circuitry is screened. The telephone pick-up coil isplaced on the base section of the telephone in the positionthat gives the best signal pick-up, and it will be necessary toexperiment a little here. Note that if the volume control isadvanced too far, or the telephone handset is placed too closeto LS1, acoustic feedback will cause oscillation and a howlingsound will be produced from LS1. Try to keep the handset

30

and LS1 reasonably well separated.The amplifier is suitable for other applications where only a

low input signal level is available (medium- and high-levelsignals would overload the input stage and cause severedistortion), and with suitable switching the circuit could beused as an intercom. The input would then be fed from a high -impedance loudspeaker of the same type as used for LS1, andthis would operate in reverse as a sort of moving -coilmicrophone. To permit communications in the oppositedirection, LS1 would be connected to the input to act as themicrophone and the other loudspeaker would be fed from theoutput of the amplifier. Figure 13 shows the switchingnecessary to achieve this, and the switch used should be abiased type which automatically switches to the "receive"position when released. The slave station can then call themain one by operating push-button switch S2 so that powerfrom the additional battery is connected to the amplifier, andthen talking into the microphone so that the attention of any-one at the main station then operates the on/off switch andthe send/receive switch (S3), and S2 can be released. The mainstation calls the slave one simply by setting Si to the "on"position, S3 to the "send" position, and talking into, themicrophone.

The circuit can be used as a baby alarm simply by feedingthe input from a high -impedance loudspeaker (used as a micro-phone) or a low -impedance dynamic microphone (i.e. the typeused with inexpensive cassette recorders). However, thecurrent consumption of the unit is high enough to makebattery operation for long periods of time rather expensiveunless rechargeable NiCad cells are used.

Components for Project 2 - Telephone Amplifier (Fig. 11)Resistors: all 1/3 watt 5% (10% over 1 M)

R1 1.2 M (brown, red, green, silver)R2 4.7 k (yellow, violet, red, gold)VR1 100 k log. carbon

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 220 nF polyester (red, red, yellow, black, red)

31

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C3 10 nF polyester (brown, black, orange, black, red)C4 100 AF' 10 V electrolyticC5 100 nF polyester (brown, black, yellow, black, red)C6 100 µF 10 V electrolytic

Semiconductors:IC 1 LM380NTrl BC109C

Switch:SI SPST miniature toggle type



80 ohmsSocket:

SKI 3.5 mm jack typeMiscellaneous:

VeroblocControl knobTelephone pick-up coilWire

33

Project 3 - Light -Activated SwitchLight -activated switches have applications in fields such asburglar -alarm systems and automatic control systems. Theyalso make interesting projects for the electronics experimenter.The circuit diagram shown in Figure 14 is for a switch of thetype that activates a relay when the light level received by thelight sensor rises above a certain threshold level, and switchesoff again when the light level falls back below the thresholdlevel. The component layout and wiring diagram for the Light -Activated Switch appears in Figure 15.

The relay coil is driven from the collector of Tr 1 , and therelay will be activated if Tr 1 is switched on by a suitable base-

current and voltage. The voltage and current available at thebase of Trl is dependent on two main factors, the resistanceprovided by PCC1, and the setting of VR1. If VR1 is set atmaximum value PCC1 needs to have a resistance of about100 k or less in order to bias Tr 1 into conduction and activatethe relay. In total darkness PCC1 has a resistance of 200 k ormore, but only a very low light level is sufficient to reduce its

PCC1RPY58A

R1

10k

VR1100 k

51on/off

DI1N4148

ofm81

9VTr1 PP6,8C109C

Fig. 14 The circuit diagram of the Light -Activated Switch

34

black

..a------- 1

. OFF -,GHJKL1.-4.--a-..... ----11-111-111- 1411-41-141

*-0-11--111-0-0 a ILW-111-0-0- i i-11-11-4111-

MI -11-41-1111- ----7 6-0-11-4- ---- 7

III -I--- 10-111-1.411ii---- it 11-1111-0-INF-. II -S- 111-11-0-41-111-111, a 1111111-0-11

a--0 -IVA 111-4111--1111-111-11

1311-41,-111- -It 11-1111111-0-0 13

--,-4.-. ..-.-4.-.-.--.,,,,,.. M-16--....-21-4.--1--c. iii -0-0-20-41111-111-41- a 41-41-111-111-18

N-,-. a -141-11-111 9 -1-11ak a i--4- lg

110-1,-0- ---111-0--5 11-- a 111-1141F-0-

5-41-11-0-4111---- 5-41-11-11-81 -- a 5 la . a, a^ t D1

,

Trt R1 PCC1

BatteryClip

PL.L,

Fig. 15 Constructional details of the Light -ActivatedSwitch

35

resistance sufficiently to switch on Tr 1 and the relay.If VR1 is set for a lower resistance level, PCC1 needs to

exhibit a lower resistance in order to bias Tr 1 into conduction,and the sensitivity of the circuit is reduced since PCC1 must besubjected to a higher light level in order to produce this lowerresistance. If VR1 is steadily adjusted lower in resistance, thesensitivity of the circuit is progressively reduced. With VR1 atvirtually minimum resistance even an extremely high level oflight will be insufficient to operate the circuit. Thus VR1 actsas a sensitivity control, and enables the light -threshold level tobe varied over extremely wide limits.

DI might at first appear to be superfluous, but it must beborne in mind that a relay coil is a highly inductive component,and this can result in a high reverse voltage being generatedacross the relay coil as it is de -energised. The purpose of D1 isto suppress this voltage pulse and prevent it from damaging Tr 1.

A pair of normally -open relay contacts are used to controlsome ancillary item of equipment, and this equipment will beswitched on and off in sympathy with the relay. The unit iscapable of controlling mains -powered equipment provided therelay used has a high enough contact voltage rating, but forreasons of safety the unit should only be used to controlmains -powered equipment if it is built as a proper casedproject. The case must be a type having a screw -on lid and nota clip -on type that would give easy access to the dangerousmains wiring. The negative supply rail of the unit should beearthed to the mains earth lead, and any exposed metalworkon the unit should be similarly earthed. Beginners would bewell advised not to use the unit to control mains equipmentuntil they have gained the necessary experience to undertakethis. safely. Until then it would be better just to regard thecircuit as a simple one to demonstrate the properties of aphotocell, or to use the relay to operate low -voltage battery -

powered equipment.

Components for Project 3 - Light -Activated Switch (Fig. 14)Resistors: 1/3 watt 5%

RI 10 k (brown, black, orange, gold)VR1 100 k lin. carbon

36

Semiconductors:Tr 1 BC109CDI 1N4148

Photocell:PCC1 RPY58A


Relay:RLA 6/12 volt coil having a resistance of 185 ohms or more,

and contacts of appropriate type and adequate rating.Battery:

B1 PP6 size 9 -volt and connector to suitMiscellaneous:


37

Project 4 - Dark -Activated SwitchThe circuit diagram of the Dark -Activated Switch is given inFigure 16, and the breadboard component layout is shown inFigure 17.

This circuit is a modified version of the previous one, andbasically VR1 and PCC1 have been swopped over. Thus, in thiscircuit a base current is allowed to flow into Tr 1 and switchthe device on when PCCI is in darkness and has a highresistance. Under bright conditions PCC1 has a low resistanceand effectively short-circuits the base of Tr 1 to earth and cutsit off. With VR1 at maximum resistance PCC1 will cut offTr 1 unless a very low level of light is present, but with VR1at minimum resistance the light threshold is raisedconsiderably, and VR1 acts as a sensitivity control much as itdid in the circuit of Figure 14. Also in common with theprevious circuit, R1 is included to ensure that an excessivebase current cannot flow into the base of Trl.

Of course, if any of the light-sensitive circuits described inthis book are constructed as permanent cased projects, the

VR1100 k

R14.7 k

Tr1BC109C

PCC1.,RPY58A''",

Sion/off

D1

1N4148

al"81

9VPP6

Fig. 16 The circuit diagram of the Dark -Activated Switch

38

VR1

black

-41-1111-4111-111---- -4F -411-11.--11-11

BCL)EF -iGHJKLD-0-11-11.-11 111-111-0-411.--111

R-0-61-11-1111

-411- 0-0-111 11-0-0-11/-A BCDEF L GHJKL31 -------e-e- 31

Batteryclip

red

Fig. 17 Constructional details of the Dark -ActivatedSwitch

39

photocell must either be fitted on the exterior of the case, orit must be mounted inside the case behind a hole drilled in thecase so that it can respond to the ambient light level.

Components for Project 4 - Dark -Activated Switch (Fig. 16)Resistors: 1/3 watt 5%

R1 4.7 k (yellow, violet, red, gold)VR1 100 k lin. carbon

Semiconductors:Trl BC109CD1 1N4148




and contacts of appropriate type and rating.Battery:

B1 PP6 size 9 volt and connector to suitMiscellaneous:


40

Project 5 - Light AlarmThis circuit produces an audio tone if the photocell is

subjected to a reasonably high level of light (normal daylightand artifical room lighting are sufficient to operate the circuit).The unit could be used as a simple burglar deterrent, and itwould then be placed in a cupboard or a drawer, and wouldproduce the alarm signal if the cupboard or drawer was openedby a burglar, hopefully unnerving him or her sufficiently tomake them leave the premises immediately. It could also beused in a medicine cupboard to sound a warning if a smallchild should somehow manage to open the cupboard. In thisapplication the on/off switch should be fitted somewhere onthe outside of the cupboard (preferably out of sight on top ofthe cupboard where a small child would be unable to reach itand probably be unaware of its existence) so that the alarmcould be switched off before opening the cupboard, andswitched on again after it has been closed. The alarm mightotherwise attract the attention of a small child.

The circuit is similar to the Light -Activated Switchcircuit described earlier, but instead of driving a relay theswitching transistor drives an audio alarm circuit. Also, a fixedresistor has been used across the base - emitter terminals of theswitching transistor so that the sensitivity of the circuitpreset. However, R4 can be raised somewhat in value ifincreased sensitivity is required. Alternatively, it can bereplaced with a 100 k linear potentiometer if variablesensitivity is required.

The audio -alarm generator uses an LM380N (IC1) in asimple audio -oscillator circuit, and driving high -impedanceloudspeaker LS1 via coupling capacitor C3. It tis a simplematter to get a non -inverting amplifier having a fairly high gainto oscillate, and it is merely necessary to provide AC couplingfrom the output to the input. Provided the losses through thiscoupling are less than the voltage gain provided by theamplifier this will give sufficient positive feedback to sustainoscillation.

The values for RI, R2, and C2 shown in the circuit diagram(Figure 18) give considerably more feedback than is needed tojust sustain oscillation, and the circuit oscillates strongly pro -

41

ducing a roughly squarewave output at a frequency in theregion of 1 kHz.

The breadboard component layout for the Light Alarm isshown in Figure 19.

Components for Project 5 - Light Alarm (Fig. 18)Resistors: all 1/3 watt 5%

RI 4.7 k (yellow, violet, red, gold)R2 4.7 k (yellow, violet, red, gold)

42

LS1

1

red

black

T

1 .--a-ar------- 1

A BCDEF- GHJKL. M

.DellOlkel

13

19

0-1111-119-11-11

111-111-111--

- INN

25

111-11141-11-111

0-41--F-111

111-1110-0-11.

kC

13

-11-11.-

CiS

all4011141

25

111-110-0111- I 111-111-11-0-11

A BCDEF -lGHJKL31 0 -111 -11 -11 -40 -1P -11-0-11P- ,

Batteryclip

Fig. 19 Constructional details of the Light Alarm

43

R3 10 k (brown, black, orange, gold)R4 10 k (brown, black, oragne, gold)

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 10 nF polyester (brown, black, orange, black, red)C3 10 µ F 25 V electrolytic

Semiconductors:ICI LM380NTrl BC109C



Battery:BI PP6 size 9 volt and connector to suit



VeroblocWire

44

Project 6 - Dark -Activated AlarmThis circuit is similar to the one just described, but it operatesan audible alarm if the light intensity received by the photocellfalls below a certain threshold level, rather than if it exceedsthe threshold level. A possible application for the unit is as alighting -up -time reminder for a car, and the circuit will operateproperly from a 12 -volt car battery instead of a 9 -volt PP6 sizebattery.

As can be seen from the circuit diagram of the unit whichappears in Figure 20, it is basically the same as the Dark -Activated Switch project described earlier, but the switchingtransistor drives an audio -alarm circuit rather than a relay. Thealarm generator is exactly the same as the one used in theLight Alarm project. VR1 is used to set the light threshold atwhich the alarm begins to sound, as was the case with theDark -Activated Switch project.

Figure 21 gives the breadboard component layout for theDark -Activated Alarm project. Incidentally, it is possible toalter the note produced by the alarm -generator circuit, anincrease in the value of RI, R2, or C2 (or more than one ofthese) producing a reduction in pitch, and vice versa.

Components for Project 6 - Dark -Activated Alarm (Fig. 20)Resistors: all 1/3 watt 5%

R1 4.7 k (yellow, violet, red, gold)R2 4.7 k (yellow, violet, red, gold)R3 10 k (brown, black, orange, gold)VR1 100 k lin. carbon

Capacitors:CI 100 nF polyester (brown, black, yellow, black, red)C2 10 nF polyester (brown, black, orange, black, red)C3 10 µF 25 V electrolytic




45

roCC 0

I

oco

URA J 1O

ciCC

4 O

N


Loudspeaker:LS1 Miniature type having an impedance in the range of 40

to 80 ohmsMiscellaneous:

VeroblocControl KnobWire

46

LS1

red

b

T -4111-0-11

0-0--41-16-11 -.-11 -1* -01 -1* -111

111 -411 -4, -*$-M 111-0-111-111-41

111-41-10411-11 111 -111 -1* -11-1113 ---- ----1110111-0-81*--1*-111-0-11

111-11,111-41-111

111-10.-11-111 $

1 !:

-111 -1* -10 _

0-14161W-111,-11$

P3 4-

R2

BCDEF L_GHJK.1 "4

Batteryclip

Fig. 21 Constructional details of the Dark -ActivatedAlarm

47

Project 7 - Light Change SwitchThis circuit differs from the two light -dependent switchcircuits described earlier in that it does not activate at anyparticular light level, but instead activates a relay if a fairlyrapid change in light level is detected. A possible applicationfor the unit is in a burglar -alarm system where it could detectthe light from a torch beam as it crossed the sensor, or perhapsthe shadow of an intruder as it fell across the sensor. It alsohas possible uses in other proximity -detector applications.

Figure 22 shows the circuit diagram of the unit, and theVerobloc component layout is shown in Figure 23.

Photocell PCC1 is connected as part of a potential divideracross the supply lines, with RI acting as the other section ofthe divider. The voltage at the junction of RI and PCC1 willvary with changes in the light level received by PCC1, butnormal changes in the ambient light level will be too slow tobe coupled by Cl to the base of Tr 1 . However, more rapidchanges, of the type that the unit is designed to detect, will becoupled to the base of Tr 1 . Of course, CI blocks the DC levelat the junction of R1 and PCC1, and the potential here is notof great consequence (and so neither is the ambient light levelreceived by PCC1).

Tr 1 is used as a high -gain common -emitter amplifier andalthough it will receive an input signal level of probably nomore than a few millivolts, the output at Tr l's collector willhave a typical peak -to -peak voltage -swing of several volts.This signal is coupled by C2 to a simple rectifier circuit whichis comprised of D1 and D2.

IC1 is an LM380N, but it is not used here as an audioamplifier. Instead it is used as a DC amplifier and relay driver.Pin 6 of ICI is given a small positive bias by R5, while R4 givespin 2 a negative bias. The positive bias to Pin 6 (which is theinverting input) therefore takes the output fully negative, andunder quiescent conditions the relay is not energised.

When the circuit is activated a strong positive DC signal isfed to the non -inverting input (pin 2) of ICI , and if this bias isstronger than the one fed to the inverting input, the output ofICI goes positive and energises the relay coil. A bias currentthen flows from the output of IC1 to the non -inverting input

48

by way of R6, D4, and D3, and this bias current holds thecircuit with ICI's output high and the relay latched in the onstate. The reason for including D3 and D4 in the feedbackcircuit is that the output of IC1 is not fully negative understandby conditions, and the voltage drop through D3 and D4ensures that the feedback circuit does not provide pin 2 witha large enough positive bias to spuriously trigger the circuit.

If S1 is operated, pin 2 of IC1 is taken to the negativesupply voltage again and the circuit is reset to its original statewith the relay switched off. It may be found that the circuittriggers at switch -on, and this is quite likely in fact. However,this is not easily avoidable, and is of little importance since i:is merely necessary to reset the circuit using SI if it shouldprove to be necessary.

An important point to bear in mind about this circuit isthat unlike the previous circuits which consume typically onlya fraction of a milliamp under quiescent conditions and can beeconomically run for long periods from a PP6 or larger size9 -volt battery, this one consumes around 11 mA and should berun from NiCad cells if it will be left operating for long periodsof time.

Components for Project 7 - Light Change Switch (Fig. 22)Resistors: all 1/3 watt 5% (10% over 1 M)

RI 1 k (brown, black, red, gold)R2 2.7 M (red. violet, green, silver)R3 4.7 k (yellow, violet, red, gold)R4 100 k (brown, black, yellow, gold)R5 1 M (brown, black, green, gold)R6 33 k (orange, orange, orange, gold)

Capacitors:Cl 220 nF polyester (red, red, yellow, black, red)C2 33µF 10 V tantalum beadC3 100 nF polyester (brown, black, yellow, black, red)

Semiconductors:ICI LM380NTrl BC109CDI 0A90D2 0A90

49

1k1R

3 4.7k

R1

C2

D2

33 iL

F 0

A90

R2

2.7

tl IH

-0"

M

CI

220

nF

'Ai

AD

1 0A90

Tr1

BC

109C

PC

C1

-RP

Y58

A

R4

R5

1M

o --

O0-

40S

1

Res

et

100

k

D3

D4

1N41

481N

4148

Fig

. 22

The

circ

uit d

iagr

am o

f the

Lig

ht C

hang

e S

witc

h

RLA 18

5 ,n,

C31

100

nF

S2

on/o

ffcO

'

1±

B1ol

m

9V PP

6 aren

Fig. 23 Constructional details of the Light Change Switch

51

D3 1N4148D4 1N4148D5 1N4148


Switches:Si Push -to -make, release -to -break typeS2 SPST miniature toggle type


Relay:RLA 6/12 volt coil having a resistance of 185 ohms or more

and contacts of the appropriate type and ratingMiscellaneous:

VeroblocWire

52

Project 8 - One -Second TimerThis very simple circuit simply pulses on a LED indicator -light briefly at one second intervals, and is suitable for use as asimple photographic timer for timing enlarger 'exposures, orlong exposures using a camera with the shutter set on "B" or"T". There are probably many other applications for a simpletimer of this type.

Refer to Figure 24 for the circuit diagram of the One -Second Timer, and to Figure 25 for the Verobloc componentlayout.

The circuit is based on a TL081CP operational -amplifierintegrated circuit, but this device is really used here as avoltage comparator. If the non -inverting input (pin 3) is takento a higher voltage than the inverting input (pin 2) the outputgoes high (i.e. it assumes a voltage nearly equal to the positivesupply voltage). If the comparative input states are reversedthe output at pin 6 goes low (i.e. a low voltage of only aboutone volt or so).

RI and R2 bias the non -inverting input to half the supplyvoltage, but R3 and VR1 will actually alter this voltage byshunting RI if ICI's output is high, or R2 if it is low. C2 willbe uncharged at switch on so that the inverting input is takento the negative supply potential, and the output will go highsince the non -inverting input must be at a higher voltage thanthe inverting one. VR1 and R3 therefore raise the voltage fedto the non -inverting input.

C2 now charges from IC1's output via R4 and R5, and thecharge voltage soon exceeds the voltage at the non -invertinginput. The output then triggers to the low state and thevoltage at the non -inverting input is reduced. C2 now dis-charges through DI, R5, and the output circuitry of IC1. AsDI bypasses high value resistor R4 during the discharge half -cycle, C2 discharges much faster than it charges. The chargevoltage therefore soon drops below the voltage at the non -inverting input and the output triggers to the high state again.C2 then commences charging once more, taking the circuitback to its original state.

Thus the unit oscillates continuously with C2 charging anddischarging, and the frequency of oscillation is controlled by

53

VR1. With VR1 at maximum resistance the change in voltageat the non -inverting input as IC1's output changes state isquite small, and the frequency of operation is relatively highsince the charge voltage on C2 has to change very littlebetween output transitions. With VR1 at minimum value thevoltage fed to the non -inverting input changes very considerably,and the charge on C2 has to change a great deal to produce thechanges in output state. This slows up the circuit action andgives a relatively low operating frequency. In practice, VR1 isadjusted to give au operating frequency of one Hertz. D2 isbriefly flashed during the brief periods that IC l's output goeslow, and VR1 is simply adjusted by trial and error to give oneflash per second using a timepiece which gives seconds -indication as a reference against which the unit is calibrated.

It is important to note that when first switched on there

R3100k_ 4.7 k

1=3gm C1

100 p.F

R2 [100 k

VR1

TIC1

6L081CP1

100 k

+ 7

4 .1R5

R4 _220 k10M*----"--1-1-

S1

on/offe'D2TI L209

=C2100 nF D1

1N4148

R61k

8119V'

PP6

Fig. 24 The circuit diagram of the One -Second Timer

54

Fig. 25 Constructional details of the One -Second Timer

55

will be a gap of more than one second before the first flashfrom D2. This is because on the first cycle C2 starts from zerocharge, whereas it retains some charge at the beginning ofsubsequent cycles. The first cycle should therefore not be usedas part of a timing period. It is easier to use a flash from D2as the start of the timing period, rather than when Si is set tothe on -period anyway.

If the unit is constructed as a permanent project VR1 canbe replaced with a preset type, and even a small (0.1 watt)type is suitable.

Components for Project 8 - One -Second Timer (Fig. 24)Resistors: all 1/3 watt 5% (10% over 1 M)

RI 100 k (brown, black, yellow, gold)R2 100 k (brown, black, yellow, gold)R3 4.7 k (yellow, violet, red, gold)R4 10 M (brown, black, blue, silver)R5 220 k (red, red, yellow, gold)R6 1 k (brown, black, red, gold)VRI 100 k lin. carbon

Capacitors:Cl 100µF 10 V electrolyticC2 100 nF polyester (brown, black, yellow, black, red)

Semiconductors:IC 1 TLO81CPD1 1N4148D2 TIL209

Switch:Si SPST miniature toggle type


Miscellaneous:VeroblocWire

56

Project 9 - MetronomeThe circuit diagram of the Metronome is shown in Figure 26,and this has obvious similarities with the One -Second Timerproject just described. In fact, ICI is used in what is basicallythe same oscillator circuit, but the component values havebeen modified to give a frequency range which is appropriateto this application. VR1 gives about 30 beats per minute atminimum value, rising to around 300 beats per minute atmaximum value, but due to the component tolerances thesefigures are only approximate. However, the unit should giveany beat rate that is likely to be needed in practice, and therange covered has purposely been made slightly wider than isreally necessary in order to allow for the effects of componenttolerances. The unit provides both an audible and a visualindication of the beat.

A small but significant difference between the One -SecondTimer and Metronome circuits is the polarity of Dl in eachcircuit. With the polarity used in the One -Second Timer theoutput of the oscillator is high for the majority of the time,and low for only very brief periods. With the polarity used inthe Metronome the opposite effect is obtained with the outputpulses being brief positive ones. LED indicator D2 in theMetronome unit is still briefly flashed on since it is connectedfrom the output of IC1 to the negative supply line, rather thanto the positive supply line, as in the One -Second Timer unit.

A normal (mechanical) metronome does not just give avisual indication of the beat rate, but it also gives an audibleindication in the form of a series of "clicking" sounds. In thiscircuit a simulation of this is provided by using the briefoutput pulses to drive a loudspeaker (LS1). ICI is not able toprovide the fairly high current needed in order to drive theloudspeaker at good volume, and Trl is therefore used as anemitter -follower stage which gives the necessary currentamplification between IC1 and [Si. R7 and R3 are thecurrent -limiting resistance for D2, and together with D2 theyalso reduce the voltage drive to Trl slightly so that an exces-sive current cannot be passed through Tr 1 during the outputpulses.

The Verobloc component layout for the Metronome is

57

ct -1'CC P.-

.zt

In

d rcr o

cor-

-r

oZi Xz

ZTO ig

0 C

011Pi+

te)

U.

N N8

CV -le

Z.;rr)

01

shown in Figure 27.If the unit is constructed as a permanent project VR1

should be fitted with a large pointer knob, and a scale calibratedin beats per minute can be marked around this. The calibrationpoints are found by trial and error, and the best rate ismeasured simply by counting the number of beat indicationsproduced in a 1 -minute period (or perhaps the number in a 20 -second period and then multiplying this figure by 3 in order to

58

Fig. 27 Constructional details of the Metronome

59

find the number of beats per minute).

Components for Project 9 - Metronome (Fig. 26)Resistors: all 1/3 watt 5% (10% over 1 M)

RI 33 k (orange, orange, orange, gold)R2 33 k (orange, orange, orange, gold)R3 1 k (brown, black, red, gold)R4 4.7 k (yellow, violet, red, gold)R5 10 M (brown, black, blue, silver)R6 100 k (brown, black, yellow, gold)R7 680 ohms (blue, grey, brown, gold)VR1 100 k lin. carbon

Capacitors:Cl 100 pf 10 V electrolyticC2 100 nF polyester (brown, black, yellow, black, red)

Semiconductors:ICl TLO81CPD1 1N4148D2 TIL209 (0.125 in red LED)Trl BC109C






60

Project 10 - "Heads" Or "Tails"This circuit electronically simulates the tossing of a coin, andit is operated by briefly depressing a push-button switch. Whilethe switch is depressed two LED indicators both light up, butonly one will remain on when the switch is released. There isno way of predetermining which LED will be the one thatremains switched on when the switch is released, and there isno bias to one or other of the LEDs. Thus, by designating oneLED "heads" and the other LED "tails", the unit gives therequired simulation of a coin being tossed.

The circuit diagram of the "Heads"Or "Tails" unit is shownin Figure 28, and the Verobloc component layout appears inFigure 29.

The circuit of the unit uses an oscillator of the same basictype as the oscillators used in the two previous projects. How-ever, an important and essential difference is that it does notuse a diode in the charge/discharge circuit for the timingcapacitor. This means that there is no difference between thecharge and discharge times, and that the output of theoscillator spends equal amounts of time in the high and lowstates.

Two LED indicators are driven from the output of IC1, butthey are driven out -of -phase. In other words, when ICI'soutput is high D2 will be switched on, and D1- will be turnedoff. With ICI's output low it is D2 that becomes switched offand D1 that is switched on. R5 and R6 are the current -limitingresistors for the two LEDs, and R7 plus R8 ensure that thevoltage across whichever LED is in the off state is sufficientlylow to cause that LED to fully switch off and not visibly glow.

The oscillator will only function properly when SI isoperated, since there is otherwise no charge or discharge paththrough R4 and the open circuit SI . When the circuit doesoscillate the frequency of operation is a few hundred Hertz,and the switching action of DI and D2 is too fast to beperceived properly by a human observer. Thus rather thanflashing, the two LEDs seem to be alight continuously, but aseach one is switched off for 50% of the time the averagecurrent fed to each LED is only half the normal level and theLEDs appear to be less bright than normal.

61

NC Jg

COL

NON 5

_J'"17:

I-

5-0 0-(7)

CC CO

54 1 M

N re,SX re)

U_1

When Si is released C2 is no longer able to charge or dis-charge through R4 and the output circuitry of ICI, and theinput voltage to the inverting input of ICI remains at whateverlevel it happened to be at the instant that the contacts of Siwent open -circuit. Thus the output of ICI stays in whateverstate it happened to be in at this instant, and the appropriateLED indicator remains switched on. There is no way of tellingin advance which LED this will be, and each LED stands an

62

Fig. 29 Constructional details of the "Heads" Or "Tails"Unit

63

equal chance of being the one that remains on since the highand low times of IC1 's output are equal. In practice, it is likelythat there will be a slight inequality here since, for example,the output circuitry of ICI is not perfectly symmetrical. How-ever, any bias to one or other of the LEDs should be far toosmall to be of any significance.

When trying the unit in practice do not be surprised if atfirst one LED seems to be dominant, and the unit does notseem to give a truly random output. This is something thatcould happen when actually tossing a coin, and it is quitepossible that tossing a coin six times, for instance, would givethe same result all six times. In order to be sure that the unitis giving a truly random answer it is necessary to note theresults of a great many operations of the unit (say a hundredor more), and there should then be a roughly equal number of-heads" and "tails". Of course, if the same answer is obtainedevery time after about a dozen operations of the unit it islikely that there is a circuit fault, and the wiring should bechecked.

Components for Project 10 - "Heads" Or "Tails" (Fig. 28)Resistors: all 1/3 watt 5%

RI 33 k (orange, orange, orange, gold)R2 33 k (orange, orange, orange, gold)R3 18 k (brown, grey, orange, gold)R4 18 k (brown, grey, orange, gold)R5 1 k (brown, black, red, gold)R6 1 k (brown, black, red, gold)R7 1.8 k (brown, grey, red, gold)R8 1.8 k (brown, grey, red, gold)

Capacitors:Cl 100 /IF 10 V electrolyticC2 100 nF polyester (brown, black, yellow, black, red)

Semiconductors:IC 1 TL081CPD1 TIL209 (0.125 in red LED)D2 TIL211 (0.125 in green LED)

Switches:SI Push -to -make, release -to -break type

64

S2 SPST miniature toggle typeBattery:


VeroblocWire

65

Project 11 - 4-60 Second TimerThis simple electronic timer switches on a LED indicatorbetween 4 and 60 seconds after switch -on. The time delay iscontinuously adjustable between these limits. Apart fromdemonstrating capacitor --resistor time constants, the unit haspossible practical applications, and it could, for example, beused as a games timer.

The circuit diagram of the timer unit is shown in Figure 30,and the Verobloc component laydut is given in Figure 31.

LED indicator Dl is driven from the output of ICI by wayof current -limiting resistor R3. D1 will be switched off whenICI's output is high, and switched on when ICI's output islow. At switch -on ICI's inverting input will be taken to thenegative supply -rail potential since C1 will not have any chargeinitially, but the non -inverting input will receive a positive bias

OR133 k

14jR41M

ON1100 k

DR233k

7'Cl+

TLOB1CP

4

C1 +33 ." reset

T

R51M

S2on/off

cs

DiTIL209

R31k

B9V;PP6

Fig. 30 The circuit diagram of the 4-60 Second Timer

66

Fig. 31 Constructional details of the 4-60 Second Timer

67

from the potential divider chain formed by R1, VR1, and R2.The output of VR1 therefore goes high and D1 is not switchedon.

Cl immediately starts to charge from the positive supplyrail by way of R5, and the charge potential on CI rises steadily.At some point the charge on Cl will be higher than the biasvoltage fed to the non -inverting input, and at this stage theoutput of IC1 will go low and D1 will light up. The length oftime it takes for this to happen depends on a number offactors, including the values of R5 and Cl. The time taken forthe charge voltage to reach 63% of the supply voltage is 1 CRseconds (with C in 1./F and R in megohms), and after 5 CRseconds the charge potential is more than 99% of the supplyvoltage. With the specified values for R5 and Cl this meansthat the charge on Cl will reach 63% of the supply voltageafter a nominal period of 33 seconds, and if VR1 is adjusted togive a potential equal to 63% of the supply voltage at the non -inverting input of IC1 the delay time of the circuit will be33 seconds.

Adjusting VR1 for a higher voltage gives a greater delaytime with a maximum of about 60 seconds being attainable.A lower voltage at the slider of VR1 gives a reduced timedelay down to a minimum of approximately 4 seconds. ThusVR1 acts as the delay time control.

R4 is included to give a small amount of DC positive feed-back over ICI, and this simply ensures that as the charge onCl starts to go above the voltage at the non -inverting input ofIC1 the output switches rapidly from the high state to the lowone so that D1 switches on abruptly, and does not graduallyswitch on (which would be an ambiguous way of indicatingthe end of the timing period).

If the timer is constructed as a permanent project VR1 canbe fitted with a large pointer knob and a scale calibrated inseconds can be marked around this. The calibration pointsmust be found by empirical means, and note that the scale willbe non-linear as Cl charges in a non-linear fashion.

68

Components for Project 11 - 4-60 Second Timer (Fig. 30)Resistors: all 1/3 watt 5%

RI 33 k (orange, orange, orange, gold)R2 33 k (orange, orange, orange, gold)R3 1 k (brown, black, red, gold)R4 1 M (brown, black, green, gold)R5 1 M (brown, black, green, gold)VR1 100 k lin. carbon

Capacitors.Cl 33 btF 10 V tantalum bead

Semiconductors:IC1 TLO81CPDI TIL209 (0.125 in red LED)



Miscellaneous:VeroblocControl knobWire

69

Project 12 - Audio -Alarm TimerThe majority of this circuit is the same as that of the 4 to 60Second Timer just described. However, it has some additionalcircuitry which produces an audio tone at the end of thetiming period in addition to the LED indicator switching on.This feature is often advantageous as it removes the need tokeep an eye on the unit so that the user does not miss theinstant when the LED indicator switches on. The timing rangeof the unit is the same as that of the original circuit, but as weshall see later on, it is very easy to modify the timing range ifdesired.

Refer to Figure 32 for the complete circuit diagram of theAudio -Alarm Timer, and to Figure 33 for the component lay-out of the circuit on the Verobloc.

The timer circuit proper is just the same as the originaltimer in every respect, and the only new circuitry is thatassociated with IC2 and D2. IC2 is used as a simple audiooscillator of a type that has been employed in earlier circuits.However, when IC1's output is high a bias current is fed fromthe output of ICI to the input of IC2 via R6 and D2. Thisbiases IC2 so that its output is fully positive and the circuit isnot able to oscillate.

When the output of ICI goes low at the end of the timingperiod only a very low voltage appears at the junction of R6and R7, and this is insufficient to overcome the forwardthreshold voltage of Dl. The bias current through DI is there-fore cut off and the oscillator functions normally, producingthe audio alarm tone.

Both timer circuits have a reset switch (Si) incidentally,and in order to start a new timing run this switch is brieflyoperated. This simply discharges C2 so that the circuit startsa fresh timing -run with C2 at zero charge when Si is released.Note that the timing -run commences when Si is released, andnot when it is depressed.

The timing range of the unit can be altered by changing thevalue of the component used in the R3 position. Raising thevalue of this component produces a proportionate increase inall the delay times, and reducing its value gives a proportionatedecrease in these times. For example, using a 10 Megohm

70

resistor for R3 would increase the timing range limits by afactor of 10, and the approximate maximum and minimumfigures would be 40 seconds to 600 seconds (10 minutes). Notethat 10 Megohms is about the maximum practical value for R3since with higher values the leakage current of C2 could causeproblems. In theory no current leaks through the insulation ofC2, but in any practical component there is a small leakagecurrent. If R3 is made too high in value the charge current willbecome little more than the leakage current and the timedelays would consequently become greatly extended. It couldeven result in the timing period not ending in an extreme casedue to the charge current only equalling the leakage current.The charge voltage on C2 would then remain static.

C2 needs to be a good quality low -leakage component, andit is for this reason that a tantalum bead capacitor has beenspecified in preference to an electrolytic type.

Components for Project 12 - Audio -Alarm Timer (Fig. 32)Resistors: all 1/3 watt 5%

RI 33 k (orange, orange, orange, gold)R2 33 k (orange, orange, orange, gold)R3 1M (brown, black, green, gold)R4 1 M (brown, black, green, gold)R5 1 k (brown, black, red, gold)R6 10 k (brown, black, orange, gold)R7 1 k (brown, black, red, gold)R8 4.7 k (yellow, violet, red, gold)R9 4.7 k (yellow, violet, red, gold)VR1 100 k lin. carbon

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 33 µF 10V tantalumC3 10 nF polyester (brown, black, orange, black, red)C4 10µF 25 V electrolytic

Semiconductors:ICI TLO81CPIC2 LM380ND1 TIL209 (0.125 in red LED)D2 1N4148

71

S2

onio

tt

RI

33 k

VR

110

0 k

CI ar,r

)w

ee

nF

R2

33 k

[R31M

TI L

209DI

1 Res

et

LC

2I:0

0

T"

IC1

TL0

81C

P

4

R4

R5

1M1k

6

R6

10 k R7 1k

C31

10 nF

D2

1N41

48

Fig

. 32

The

circ

uit d

iagr

am o

f the

Aud

io -

Ala

rm T

imer

14IC

2LM

38O

N

3, 4

, 510

,11,

12

R8

4 7

k

IR

94

7 k aI

7

C4

10 µ

F

OF

LStE

(40

-80 ,C1

B1

9V PP

3 me.

Fig. 33 Constructional details of the Audio -Alarm Timer

73






74

Project 13 - Simple OscillatorThis simple audio oscillator produces roughly a sinewave out-put at a frequency of about 500 Hertz. It is suitable for use asa general-purpose audio signal source for use in the home elec-tronics workshop, or if the output is coupled to a crystalearphone and the on/off switch is replaced with a Morse keythe unit can be used as a Morse code practice oscillator.

The circuit diagram of the Simple Oscillator can be foundin Figure 34, and the Verobloc component layout for thisproject is illustrated in Figure 35.

The circuit is little more than a basic phase -shift oscillator,and this type of circuit uses positive feedback between theinput (base) and output (collector) of a high -gain commonemitter -amplifier. However, the base and collector of acommon emitter stage are out -of -phase, and any straight.forward feedback between the two will be negative rather thanpositive. This is overcome by using three phase -shift circuits inthe feedback path, and each phase -shifter gives a 60 degreephase -shift or 180 degrees through the three circuits, givingpositive feedback rather than the negative variety. Providedthe gain of the amplifier exceeds the losses through the phase -shift network the circuit will oscillate at the frequency wherethe phase -shift network gives the 180 degree phase shift.

In this circuit Tr 1 is used as a conventional common -emitter stage having RI as the collector -load resistor and R2 toprovide base biasing. C2 plus R4 forni the first phase -shiftcircuit, and C4 plus R3 form the second. The third section iscomprised of C3 plus the input impedance of Tr 1 .

As the gain of Tr 1 is somewhat more than the lossesthrough the phase -shift network the circuit does oscillate, butthere is not a great excess of gain provided by Trl, and thecircuit does not oscillate very strongly. As a result of this theoutput waveform is roughly sinewave, although there is asignificant harmonic content on the output (harmonics aresimply signals at frequencies which are multiples of the funda-mental output frequency). This reasonably pure signal makesthe unit a good general-purpose test oscillator or Morsepractice oscillator.

Cl couples the output signal from the collector of Trl to

75

Fig. 34 The circuit diagram of the Simple Oscillator

volume control VR1, and from here the signal is taken to theoutput socket.

Components for Project 13 - Simple Oscilator (Fig. 34)Resistors: all 1/3 watt 5% (10% over 1 M)

RI 4.7 k (yellow, violet, red, gold)R2 1.2 M (brown, red, green, silver)R3 18 k (brown, grey, orange, gold)R4 18 k (brown, grey, orange, gold)VR1 100 k log. carbon

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 10 nF polyester (brown, black, orange, black, red)C3 10 nF polyester (brown, black, orange, black, red)C4 10 nF polyester (brown, black, orange, black, red)

Semiconductor:Trl BC109C

76

S1

A1 REF3

red

black

Batteryclip

Fig. 35 Constructional details of the Simple Oscillator

77



Socket:SKI 3.5 mm jack type


78

Project 14 - Loudspeaker OscillatorWhen used as a Morse practice oscillator the circuit of Figure36 may be preferred to the basic circuit just described, as thecircuit of Figure 36 has an additional output stage whichenables a loudspeaker to be driven at good volume.

The basic tone -generator circuit is the same as before, buta resistor (R5) has been added at the output of the unit. Thisis used merely to reduce the output level of the unit whichwould otherwise be excessive and would fully drive the outputstage even with the volume control set well back.

The output stage is a straightforward amplifier based on theLM380N, and this drives a high -impedance loudspeaker (LS1)via DC blocking capacitor C6.

Figure 37 shows the Verobloc component layout for theLoudspeaker Oscillator.

Components for Project 14 - Loudspeaker Oscillator (Fig. 36)Resistors: all 1/3 watt 5% (10% over 1 M)

RI 18 k (brown, grey, orange, gold)R2 18 k (brown, grey, orange, gold)R3 1.2 M (brown, red, green, silver)R4 4.7 k (yellow, violet, red, gold)R5 1 M (brown, black, green, gold)VR1 100 k log. carbon

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 10 nF polyester (brown, black, orange,black, red)C3 10 nF polyester (brown, black, orange, black, red)C4 10 nF polyester (brown, black, orange, black, red)C5 100 nF polyester (brown, black, yellow, black, red)C6 10 AF 25 V electrolytic




79

00C

1.1.

100

nF

18 k

C2

K)

nF

RA

47k

R3

1.2

M

C3

C4

10 n

F10

nF

R2

18 k

Tr1

BC

109C

C5

100

nF

Fig

. 36

The

circ

uit d

iagr

am o

f the

Lou

dspe

aker

Osc

illat

or

2IC

1LM

MIO

N

3, 4

, 5,

10,1

1,12

cf S

1

on/o

ff

C6

10 iL

F 11-

LS1E

(40-

80

Tr

S1

red

BatteryClipclip

block

1

A CD ELCDEGHJK1 i05i

7 4. -*-111111-134 , a

eb

N C4

R2

* 411-- *Al111-0-111-11-41

111.-0-111-0-11113

-"-Ft S1C3

0-1P-- 11,1

11-41-11-111-41

R. 11.11P-11.

. Z 4-0

31

Fig. 37 Constructiona details of the LoLdspeakerOscillator

81




82

Project 15 - Tone GeneratorThe simple Tone Generator circuit of Figure 38 has sufficientoutput to drive a high -impedance loudspeaker at good volume,and in a single range it covers a frequency span of about 100Hertz to 2 kilohertz.

The circuit uses an oscillator of a type which has beenemployed in prevous projects in this book, and it really justconsists of a non -inverting amplifier using an LM380N devicewith feedback provided from the output to the input via R2,VR1, C3, and R1. As was mentioned in an earlier section ofthis book, the frequency of oscillation can be altered by

changing the values of any of these components, withincreased value giving decreased operating frequency, and viceversa.

In this circuit by making the series -feedback resistor (i.e.the combined resistance of R2 and VR1) variable theoperating frequency of the unit can be varied. With VR1 atmaximum resistance the operating frequency is at its minimumfigure of approximately 100 Hertz (a deep tone) and atminimum resistance the operating frequency reaches itsmaximum figure of very roughly 2 kilohertz.

Figure 39 shows the Verobloc component layout for theTone Generator. Those who like to experiment might like totry changing the values of the components in the feedbackcircuit to see what effect this has on the frequency span of theunit.

Components for Project 15 - Tone Generator (Fig. 38)Resistors: all 1/3 watt 5%

RI 4.7 k (yellow, violet, red, gold)R2 4.7 k (yellow, violet, red, gold)VR1 100 k lin. carbon

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 100 µF 10 V electrolyticC3 10 nF polyester (brown, black, orange, black, red)C4 10 µF 25 V electrolytic

Semiconductor:ICI LM380N

83






84

Batteryclip

LS1

red

black

S1

I

0 Li 0

VR1

1 -ass---atBCCEF GHJKL11-111-111-11-111 111-11-0-111-11

=I=111-1111-

11-111--111-1111-1111 1111-111,111-11-411

7 tee-- e----11-41-111.-0-11

N-1111--111-10-111 WAS a4`1"jih13

19

16-11-111-111-1111

111-0-464-111

25 ----a ---- 2 5110111111-410

1-111-0-111-41

111,110,111-111-0

5-U 111-1111-0-111-111

11111111110-111

A BCCEF GHJKL M31 s -a-- 1,-*--e-e- 31

Fig. 39 Constructional details of the Tone Generator

85

Project 16 - Warbling DoorbuzzerA simple electronic doorbuzzer could simply consist of anoscillator driving a loudspeaker, but this arrangement is lessthan ideal in that a simple audio tone tends to be easilymasked by other sounds, and it would be ineffective. Oneway around this problem would be to have a very loud audiotone, but this has the disadvantage of being annoying or evenunpleasant to anyone who happens to be close to the loud-speaker when the unit is activated.

A much better, although less obvious alternative, is to use amodulated tone of some kind at only moderate volume. By amodulated tone, we simply mean one that is varied in eitherfrequency or volume. Varying the volume of the signal,perhaps by just pulsing the signal on and off, can be quiteeffective, but some method of frequency modulation is usuallya little more effective. Frequency modulation is usually morepleasing to the ear as well, which is an advantage for somethingthat is for use in the home.

The tone produced by this doorbuzzer circuit is frequencymodulated, and the simplest form of frequency modulation isused. The tone is simply switched backwards and forwardsbetween two pitches, and this gives a sort of warbling effectwhich is quite effective. The full circuit diagram of the unitappears in Figure 40, and the component layout for the bread-board is shown in Figure 41.

The tone -generator circuit is based on IC2 and uses a circuitconfiguration that has been used in a number of projectsdescribed earlier in this book. If Trl is switched off, the feed-back components which set the frequency of operation areR8, R9, and C4. However, if Tr 1 is switched on it effectivelyshunts R7 across R8, and reduces the value of R8. Thisincreases the operating frequency of the tone generator andthe required frequence modulation can thus be obtained bypulsing Trl on and off.

This is achieved using a second oscillator based on IC1, andthis also uses a type of oscillator which has been used inprevious designs in this book, and it will not be described againhere. ICI oscillates at a frequency of a few Hertz, and itswitches Tr 1 on when its output goes high, and off when its

86

output is low.You may wish to try experimenting with some of the

component values to see if you can obtain an output whichyou prefer to the one produced using the specified values.Increasing the value of R4 decreases the rate of modulation,while using a lower value increases the modulation frequency.Making R9 higher in value reduces the two tones, and makingit lower in value has the opposite effect (the same is true if thevalue of C4 is changed). Reducing the value of R7 increasesthe frequency difference between the two tones, andincreasing its value has the opposite effect.

Of course, if the unit is constructed as a permanent projectSi would not be a panel mounting push-button switch, butwould be a normal bell -push mounted on the door or thedoor frame (bell -pushes can be obtained from electrical shops,incidentally).

Components for Project 16 - Warbling Doorbuzzer (Fig. 40)Resistors: all 1/3 watt 5%

RI 33 k (orange, orange, orange, gold)R2 33 k (orange, orange, orange, gold)R3 100 k (brown, black, yellow, gold)R4 1 M (brown, black, green, gold)R5 18 k (brown, grey, orange, gold)R6 4.7 k (yellow, violet, red, gold)R7 18 k (brown, grey, orange, gold)R8 10 k (brown, black, orange, gold)R9 10 k (brown, black, orange, gold)

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 100µF 10 V electrolyticC3 100 nF polyester (brown, black, yellow, black, red)C4 10 nF polyester (brown, black, orange, black, red)C5 10µF 25 V electrolytic

Semiconductors:ICI TLO81CPIC2 LM380NTrl BC109C

87

cc

1C1

X10

0nF

C2

=10

0

RI 33

kR

310

0 k

R2-

33 k

+7

IC1

TL0

81C

P

R4

C3

1 M

100

utim

nF

4

6

R5

18 k R6

4 7

k

Tr1

BC

109C

C4

aria

10 n

FM

I5

R7

18 k

-41-

6

R8

10 k

IC2

LM38

0N14

3,4,

510

,11,

12

7

R9

10 k

e

oS1

on/o

ff

LS1E

(0-8

0

4

B1

9V PP

6

Fig

. 40

The

circ

uit d

iagr

am o

f the

War

blin

g D

oorb

uzze

r

1 .-x-- ----- IA BCDEF - GHJKL M

Batteryclip

Fig. 41 Constructional details of the WarblingDoorbuzzer

89

Switch:Si Push -to -make, release -to -break type


Loudspeaker:LS1 Miniature type having an impedance in the range 40

to 80 ohmsMiscellaneous:

VeroblocWire

90

Project 17 - Two -Tone Train HornThis is a simple sound effect accessory for a model railway, andit generates a sound which is similar to that produced by thehorns used on most modern British Rail locomotives. In otherwords, it produces an initial fairly low-pitched tone, followedafter about half a second or so by a small rise in pitch. Thissecond signal continues until the on/off switch (which is apush-button switch) is released.

Figure 42 shows the complete circuit diagram of the unitand the component layout for the breadboard is given inFigure 43.

IC2 is used as the tone generator, and this device is used ina circuit configuration that has been utilized in several of theprevious projects. The rise in pitch is generated by switchingon Trl , which then effectively shunts VRI across R6. VR1 isadjusted to give a rise in pitch of the correct amount so that areasonably realistic -sounding output is obtained.

ICI is used in a simple timing circuit which gives the basebias to Trl about half a second or so after switch -on so thatthe rise in pitch is obtained automatically. R2 and R3 bias theinverting input of ICI to about half the supply voltage, butzero voltage is applied to the non -inverting input as Cl will beuncharged. However, Cl quickly charges by way of RI andafter roughly half a second the voltage at the non -invertinginput exceeds that at the inverting input. ICI's output thengoes high and switches on Trl .

R4 and R5 are used to ensure that the voltage fed to thebase of Trl when ICI's output is low is not high enough tobias Trl into conduction. DI quickly discharges Cl into thesupply lines at switch -off so that the circuit is immediatelyready to operate properly again, and the unit will functionproperly if Si is operated several times in quick succession.

VRI is given the correct setting using trial and error togradually tune the higher tone to the correct pitch. If the unitis constructed as a permanent project VR1 could be made apreset component rather than a panel -mounted control as onceit has been given the correct setting it should require nofurther adjustment.

91

10 MR

I jD

IA

IN 4148

]R210

0k

C1.

2.10

0 nF

+ 'Cl

7

TL0

84C

P

1R310

0k

a

4R

433

k R5

10 k

C4

100

µF O

mci

-m

10 n

FC

241.

VR

1W

PM

100

k2

1C2

-I)-

-- L

M38

0Nt_

____

.T

r1 BC

109C

..k.R

618

k...

.

Fig

. 42

The

circ

uit d

iagr

am o

f the

Tw

o -T

one

Tra

in H

orn

14

3, 4

, 5,

10,1

1,12

R7

S1

on/o

ff-L

L0

0

C5

dim

100

nF

33 k

Ia

1--

C3

10µF LS

1 1:

(40

-80 A

VR1

LC1

S1

0 -41 -la -41-11a-111-411-0-0a . sea fe 11 11 i .

C 111.-0-4

1910.16

ft7

IF -0-1111-41-0 81-111-11-1F111

A BCDEF - GHJKL31 Ii---0----a-a-in 31

redBattery

clipclip

Fig. 43 Constructional details of the Two -Tone Horn

93

Project 18 - Falling -Tone VersionA train horn does not necessarily produce a higher pitchedsecond tone, and sometimes the higher pitch is the initial oneand is followed by the lower tone. The circuit of Figure 42 iseasily modified to give this alternative mode of operation, andthe modified section of the circuit is shown in the circuitdiagram of Figure 44. It is only the timer section of the unitthat is changed, and the tone generator is exactly the same asin the original design.

In fact the timer circuit is not substantially different, andthe modification merely consists of swopping over theconnections to the inputs of IC1. Thus the output is normallyhigh and the higher pitch is produced, and the output swingslow when the charge on Cl takes the inverting input to ahigher potential than the non -inverting input. Trl is then cutoff and the lower pitch is produced.

The Verobloc component layout for the falling pitchversion of the Two -Tone Train Horn appears in Figure 45, andthis only shows the modified section of the layout.

Components for Projects 17 & 18 -Two -Tone Train Horn(Either Version) (Figs. 42 and 44)

Resistors: all 1/3 watt 5% (10% over 1 M)R1 10 M (brown, black, blue, silver)R2 100 k (brown, black, yellow, gold)R3 100 k (brown, black, yellow, gold)R4 33 k (orange, orange, orange, gold)R5 10 k (brown, black, orange, gold)R6 18 k (brown, grey, orange, gold)R7 33 k (orange, orange, orange, gold)VR1 100 k lin. carbon

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 10 nF polyester (brown, black, orange, black, red)C3 10µF 25 V electrolyticC4 1001.1F 10 V electrolyticC5 100 nF polyester (brown, black, yellow, black, red)

Semiconductors:IC1 TLO81CP

94

4 D1N14148R110 M

R2100 k

2

C 1

nF

7IC1TL08 CP

R3100 k

6

R44 33k

R510 k

+ve.

Tr1 bose

Fig. 44 Modified Two -Tone Horn circuit diagram

ve.

Batteryclip -ve.

V121

Fig. 45 The modified component layout for thealternative version of the Two -Tole Horn

S1

95

1C2 LM380NTrl BC109CDI 1N4148

Switch:S1 Push -to -make, release -to -break type





96

Project 19 - Simple Touch -SwitchThe advantage of a touch -activated switch over a mechanicalswitch is simply that there are no moving parts in a touch -activated type. This means that a touch -switch does not wearout, and it should have an operating life equal to the rest ofthe equipment. Another attraction of this type of switch issimply its novelty value.

This very simple design is of the type where touching twocontacts results in some item of equipment being switched on,and the equipment is switched off again when the operator'sfinger is removed from the contacts. There are two main waysof obtaining a switching action from touch contacts, and oneof these is to use stray RF and AF signals picked up in theoperator's body to activate the switching circuitry. The otheris to use the skin resistance across two contacts to activate theswitching circuitry. The second method is probably the morereliable of the two, especially where battery operated equip-ment is controlled by the touch -switch and it is not possible torely on a strong "mains hum" signal to activate the circuit. Itis therefore this method that has been adopted here.

The circuit diagram of the Simple Touch Switch is given inFigure 46, and the Verobloc component layout appears inFigure 47.

As the circuit stands, Trl will not receive any base biascurrent and is therefore cut off. Tr2 is also cut off as it doesnot receive any base bias via Trl. Thus no significant current isapplied to the load, which in this case is a relay and LEDindicator D2 plus its series current -limiting resistor R3.

If someone touches the two touch contacts a skin resistanceof between a few hundred kilohms and a few megohms will bepresent across the two contacts. This gives only a modest basecurrent to Trl of typically only about 10µA, but this currentis amplified and then fed into the base of Tr2. The amplifiedcurrent is sufficient to bias Tr2 into saturation and the loadreceives virtually the full supply voltage (there is a smallvoltage drop of about half a volt across Tr2 but this is toosmall to be of real significance). If the operator's finger isremoved from the touch contacts the base current to Trl willbe removed, and so will that to Tr2, so that Tr2 switches off

97

and power is removed from the load again. R1 and R2 arecurrent -limiting resistors which are needed to protect the basecircuits of Tr 1 and Tr2 if a short circuit should be placedacross the two touch contacts.

The unit is used to operate a relay and a LED indicatorsimply as these are convenient ways of showing that theswitching action is taking place. The unit can be used tocontrol any piece of 9 -volt battery -operated equipment whichhas a maximum current consumption of no more than 100 mA(which is the maximum current that the BC179 device canhandle safely). Make sure that the load is connected with theright polarity. The positive supply is taken from the collectorof Tr2 and the negative supply is taken from the negativesupply rail of the touch switch circuitry.

The touch contacts can be a couple of fairly large (e.g. M4size) panel -head screws, or proper touch contacts can beobtained from some of the larger component retailers andwould obviously give a very neat and professional finish to theunit. When the circuit is tested on the Verobloc breadboard a

Touch concoct:0

ER1tO k

R24.7 k

Tr1

BC109C

D11N4148

Tr2BC179

RLA185 41RLA1

'1R31k

B19V

PP6

r02T1L209

Fig. 46 The circuit diagram of the Simple Touch -Switch

98

1

A BCDEF GHJKL M

Trl

a-111--11-4-1 i D-111-111-15-5

11-11-111-45..a

5111-111-11H

11/-0.-11F1H111 -11 -*-11F0

7 11H1 -0-4H11-0-11-11-1014-0--111-0-11

111-11H-411 3 a -UHF -1H

1H-41,-0-111IF111-11.-0-111

SHO-0.-0-4111-49-41H-011-11-11-0-11

1 9 1.----.16 -1F11 -11H

25

A31

01) 111-11F-1. 31

4

r2

iiRLA

red

black

Touchcontacts

Batteryclip

Fig. 47 Constructional details of the Simple Touch -Switch

99

couple of bare wires should suffice as the touch contacts,although these will not give good sensitivity unless thick wireis used due to low surface area of the contacts.

The current consumption of the unit in the off state isnegligible since only, minute leakage currents flow in thecircuit. In the on state the current consumption is equal tothat of the load plus about 2 mA or so.

Components for Project 19 - Simple Touch -Switch (Fig. 46)Resistors: all 1/3 watt 5%

RI 10 k (brown, black, orange, gold)R2 4.7 k (yellow, violet, red, gold)R3 1 k (brown, black, red, gold)

Semiconductors:Trl BC109CTr2 BC179D1 1N4148D2 TIL209 (0.125 in red LED)


and contacts as required (see text)Battery:


VeroblocTouch contacts (see text)Wire

100

Project 20 - Touch -SwitchThe touch switch described in the previous section of thisbook is unsuitable for use in many applications because itdoes not latch in the on state, and in order to keep the con-trolled equipment switched on it is necessary to continuouslytouch the two contacts.. This can be overcome by using acircuit that does latch in the on state, and also has some meansof resetting the circuit to the off state.

This simple circuit has these features, and the load is con-trolled via two pairs of touch contacts. Touching one set ofcontacts switches the load on, and the other set of contactsare operated in order to switch the load off again. The circuitdiagram of the Touch -Switch is shown in Figure 48, and theVerobloc component layout appears in Figure 49.

The circuit used to switch on the load is basically the sameas that employed in the Simple Touch -Switch project describedearlier. However, R5 is an additional resistor which keeps Tr2switched on when the operator's finger is removed from thetwo "on" touch contacts. This gives the circuit the requiredlatching action.

Operating the two "off" touch contacts results in Tr 1 beingswitched on by the small base -current it receives. This reducesthe base -voltage of Tr2 to an insufficient level to keep thiscomponent in conduction, and both Tr2 and Tr3 switch off.When the operator's finger is removed from the two "offcontacts the circuit remains in this state since the collector ofTr3 will be at zero volts, and R5 will not provide Tr2 with abase -current. Thus, once again, the required latching action isrequired.

The notes on constructing and using the Simple Touch -Switch also apply to this design and will not be repeated here.

Components for Project 20 - Touch -Switch (Fig. 48)Resistors: all 1/3 watt 5%

R1 10 k (brown, black, orange, gold)R2 4.7 k (yellow, violet, red, gold)R3 10 k (brown, black, orange, gold)R4 4.7 k (yellow, violet, red, gold)R5 1 M (brown, black, green, gold)

101

ddb

o00

CD rto-

77' 0 0 0- 4-r

CD

00 0

off(1

)Tou

ch

°con

tact

s

fiR110

k

/Tou

ch°c

onta

cts

10 kR3[

R4

-f4.

7 k

R2

47 k

on

Tr1 BC

109C

Tr3

BC

179

R6

1kai

mB

1R

59V

-rD

1

1MP

P

-L_,

4D

2T

r 2

RLA

1N41

48T

IL20

9B

C10

9C18

5 n,

Fig

. 48

The

circ

uit d

iagr

am o

f the

Tou

ch -

Sw

itch

1 -1110-411-11-----1111-411-0-11111--M 1

A BCDEF FIGHJKL M41-11-111-111 11111-111-41-11-111

11-4111-110, 1111-11-111-0-111

0-1111-11-0 1110-i-0-41-111-0-1111 11-11-111--0-111

1111-0-0-111-411 ID -111-1-11-1117 s---- --a-ii-N 711-111110-1111-1111

111-1111-4111-0-11 111-411. -1111-0-1111

*--111F-0-111141 0-1111-1114111

111-11H10-0-111 1.-1111111-11111

11-0-11114111-41 1111111-0-0-1013..-.-.. 135-11-111-0-4111 0-111-11-0-111

Tr e -111-11F-11-011 1111-11-111-1111--M

111-11.-111-111-

e

T

e

A31

111-11-0-11-411

111-11-1111-111-

r.

4MIII I-1

4: MUM40 IP 1111rjumVir

11-11.111-0-41

01

41

F 6 G

$

19'

RLA

Off touchcontacts

On touchcontacts

red

black

Batteryclip

Fig. 49 Constructional details of the Touch -Switch

103



contacts as required (see text)Miscellaneous:

VeroblocTouch contacts (see text)Wire

104

Project 21 - Transistor CheckerSome means of testing transistors is virtually a necessity forthe home electronics workshop, and for most purposes it isnot necessary to have a highly complex and expensivetransistor analyser. All that is really needed is a simple andinexpensive device that will give "go/no-go" checks on themajority of transistor types. This project is suitable for quickchecks on silicon transistors (the type normally employed inmodern designs), and can be used with PNP and NPN types.It is not really suitable for use with germanium devices,although these are nearly all obsolete and are very uncommonthese days. It is not suitable for use with special types oftransistor such as FET and unijunction types, but this is afailing of many transistor -tester designs, including some quitesophisticated and expensive ones.

In order to test a device it is simply plugged into the unit,and separate sockets are provided for PNP and NPN devices. Ifthe device is functioning properly a LED indicator will pulseon and off at roughly 2 Hertz (i.e. two flashes per second).Separate LED indicators are used for NPN and PNP devices.

Refer to Figure 50 for the circuit diagram of the TransistorChecker, and Figure 51 for details of the Verobloc componentlayout and other wiring.

The circuit is basically just an oscillator using a LM380Ndevice in a configuration which has been utilized in severalearlier projects. However, the timing component values (RI,C2, and R2) are much larger in this circuit so that the circuitoperates at a subaudio frequency of just a couple of Hertz.There is sufficient feedback to produce strong oscillation andthe output waveform is virtually a squarewave.

If we consider the unit in the NPN mode first, tvith a testdevice (TrN) connected in circuit this device will be cut offwhen IC1's output goes low, and biased hard into conductionwhen IC1's output goes high. The collector load for the testdevice is LED indicator DI and its current limiting resistorR.S. Dl therefore lights up each time IC1's output goes high,and Dl therefore flashes on and off to indicate that the testtransistor is serviceable.

If the test device should happen to have a short circuit

105

between the base and collector terminals this will result in aforward bias being applied to D1 each time ICI's output goeslow, but the bias current will be too low to operate D1properly and it will be obvious that the test device is faulty. If

106

Fig. 51 Constructional details of the Transistor Checker

107

the test device is closed circuit D1 will simply glow contin-uously, and it will fail to light at all if the test transistor isopen circuit.

The circuit works in much the same way in the PNP modeexcept that the base terminal is fed from the output of IC1 viaR6 and R7, D2 and R8 are the LED indicator and currentlimiting resistor, and the test device is pulsed on when IC1'soutput is low rather than when it is high.

Most transistors will plug into the Verobloc without anydifficulty and there is no difficulty in using the breadboardedversion of the unit. When initially testing the unit a BC109Ccan be used for TrN and a BC179 can be used for TrP. If theunit is constructed as a permanent project the test devicesmust be connected to the unit via two sets of three socketsfitted on the front panel of the unit and 1 mm wander socketsare suitable. If these are closely grouped in sets of three itshould be found that most devices can be plugged directly intothem. A set of test leads terminated in crocodile clips can beused to make the connections to devices that will not plugdirectly into the sockets. Use wire of a different colour for eachlead so that they are easily identified and there is little risk ofinadvertently connecting the test device incorrectly.

The table given below should help the user to correctlyinterpret the results obtained when using the unit.

- LED indicator flashes from fully off to fully on; test devicefully serviceable.

- LED flashes dimly; short circuit between collector and base.- LED lights continuously; collector - emitter short circuit.- LED fails to light; collector-emitter open circuit.

Components for Project 21 - Transistor Checker (Fig. 50)Resistors: all 1/3 watt 5% (10% over 1 M)

RI 100 k (brown, black, yellow, gold)R2 2.7 M (red, violet, green, silver)R3 10 k (brown, black, orange, gold)R4 4.7 k (yellow, violet, red, gold)R5 1 k (brown, black, red, gold)R6 10 k (brown, black, orange, gold)

108

R7 .4.7 k (yellow, violet, red, gold)R8 1 k (brown, black, red, gold)


Semiconductors:ICI LM380NDI TIL209 (0.125 in red LED)D2 TIL211 (0.125 in green LED)

Switch:S1 Push -to -make, release -to -break type



109

Project 22 - Reaction GameOn the face of it this is a very simple reaction -testing gamewhch should not prove at all difficult to complete, but it isactually a little more difficult than may at first appear. Theunit has a LED indicator which flashes on and off at typicallya little under 1 Hertz (i.e. a little less than once per second),and the idea of the game is simply to hold down a push buttonswitch during the periods when the indicator light is switchedoff. This charges up a capacitor, and when the charge hasreached a sufficiently high level there is a second LED whichswitches on to indicate that the game has been successfullycompleted.

While it might seem that all one has to do is to contin-uously hold the switch down, this is not in fact correct andwill not result in the completion of the game. The reason forthis is simply that during the periods when the flashing LED isswitched on, if the push button switch is operated the chargeon the capacitor is almost instantly removed. Thus, in order tocomplete the game it is necessary to make sure that the pushbutton switch is never operated while the flashing LED isswitched on. Remember, even if the required charge has nearlybeen reached, momentarily operating the switch at the wrongtime takes you virtually right back to the beginning again.

The circuit diagram of the Reaction Game can be found inFigure 52, and the Verobloc component layout is illustratedin Figure 53.

ICI is used in a simple oscillator circuit operating at a lowfrequency and driving LED indicator DI which is flashed onduring negative output half -cycles from IC1. The invertinginput of IC2 is fed from charge storage capacitor C3 while thenon -inverting input is biased to about 75% of the supplyvoltage by R4 and R5. Initially C3 will carry no charge andwill supply zero volts to the inverting input of IC2, and IC2'soutput therefore goes high. LED indicator D2 is switched offat this stage.

If Si is closed while IC1's output is high (and DI isswitched off) C3 will charge from the output of ICI via R3.If S1 is operated at the correct times the charge on C3gradually builds up until the voltage fed to IC2's inverting

110

input is greater than the bias voltage fed to the non -invertinginput. The output of IC2 then goes low and D2 switches onto indicate that the game has been successfully completed.

If Si should be closed while ICI's output is low (and D1 isswitched on) the charge on C3 will almost instantly be lostthrough D3 and the output circuitry of ICI.

Components for Project 22 - Reaction Game (Fig. 52)Resistors. all 1/3 watt 5%

R1 1 M (brown, black, green, gold)R2 1 k (brown, black, red, gold)R3 100 k (brown, black, yellow, gold)R4 33 k (orange, orange, orange, gold)R5 100 k (brown, black, yellow, gold)R6 1 k (brown, black, red, gold)

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 220 nF polyester (red, red, yellow, black, red)C3 33 µF 10 V tantalum bead

Semiconductors:IC1 LM380NIC2 TLO81CPD1 TIL209 (0.125 in red LED)D2 TIL211 (0.125 in green LED)D3 1N4148

Switches:S1 Push -to -make, release -to -break typeS2 SPST miniature toggle type



111

S2

on/o

ff

C21

220 nF

1:)1 TIL

209

R2

1k

H4

33 k

2

IC2

D2

TIL

211

R6

71k

IC1

R1

141M

LM38

0NR

310

0 k

TL0

681

7C

P

I.4

9V3,

4,5,

D3

PP

6

Nam

C1 10

0 nF

10,1

1,12

1N 4

14 8

R5

100k

117_

4C

3 ai

r33

µF

Fig

. 52

The

circ

uit d

iagr

am o

f the

Rea

ctio

n G

ame

111-0-11-0-111

111-111-111-0-E

11-0-111-11-111

1H--111-0-41 HA BCDEF LJ GH.JKL M

31 31

Fig. 53 Constructional details of the Reaction Game

113

Project 23 - Sound -Activated SwitchThe most common uses for sound -activated switches areprobably the automatic control of tape recorders and radiotransceivers, but no doubt there are numerous other applica-tions for this type of equipment. The simple design featuredhere can be activated by speech at normal volume at a range ofup to about 1 metre or so, and this is adequate for mostpractical applications. Higher sensitivity is not really a goodidea as it is merely likely to lead to spurious operation of thedevice, and has no real advantages under normal operatingconditions. The microphone used in the unit is a highimpedance loudspeaker which is used in reverse as a sort ofcrude moving coil microphone. This does not give very goodsound quality, but as the microphone is only used to producea signal which is amplified and used to control a relay (whichin turn operates the controlled equipment) this is of noconsequence.

Figure 54 shows the circuit diagram of the Sound -ActivatedSwitch and the component layout of the breadboard and otherwiring of the unit are illustrated in Figure 55.

ICI is used as a straightforward inverting amplifier havinga voltage gain of approximately 80 dB (10,000 times), althoughthe gain is substantially less than this at higher audio fre-quencies since IC1 simply is not able to give such a highvoltage gain at these frequencies. It is necessary to use thislarge amount of amplification due to the very low signalvoltage provided by the microphone, which will normally beless than a millivolt.

The output from IC1 is coupled by C3 to a rectifier andsmoothing circuit which consists of D1, D2, C4, and R5. Thisproduces a positive DC bias which is fed to the inverting inputof IC2. This circuit produces a DC signal that has a fast attacktime so that the unit quickly responds to the commence-ment of an input signal and almost instantly switches on thecontrolled equipment. However, the decay time is muchslower, and this is advantageous since it prevents the con-trolled equipment from being switched off during brief pausesof the type that occur in normal speech.

IC2 is used as the relay driver, and R6 provides a small

114

positive bias to the non -inverting input of this device. Thiskeeps the output in the high state and the relay switched offuntil a suitably strong input signal produces a strong enoughbias at the inverting input of IC2 to send the output low andthus switch on the relay.

The unit is capable of controlling practically any item ofelectronic or electrical equipment, but make sure that therelay you use has contacts that are up to the task and are notbeing overloaded. In its breadboarded form the unit cannotcontrol a piece of mains -operated equipment as this wouldleave dangerous mains wiring exposed. It can be used tocontrol mains operated equipment if it is constructed as apermanent project and the necessary safety precautionsare observed. However, it would be inadvisable for inexper-ienced constructors to use the unit to control mains poweredequipment.

Components for Project 23- Sound -Activated Switch (Fig. 54)

Resistors: all 1/3 watt 5% (10% over 1 M)R1 1 k (brown, black, red, gold)R2 100 k (brown, black, yellow, gold)R3 100 k (brown, black, yellow, gold)R4 10 M (brown, black, blue, silver)R5 100 k (brown, black, yellow, gold)R6 1 M (brown, black, green, gold)

Capacitors:Cl 1 pF 63 V electrolyticC2 2.2 pF 63 V electrolyticC3 4.7 pF 63 V electrolyticC4 10 p F 25 V electrolyticC5 100 nF polyester (brown, black, yellow, black, red)C6 100 pF 10 V electrolytic

Semiconductors:ICI TLO81CPIC2 LM380NDI 0A90D2 0A90D3 1N4148

115

R1 1k C

1

mum

1µF

)=1L

S1

40-

80,C

1

R2

100

k

27

IC1

TL0

81C

P

C2

R3

2 2µ

F10

0 k

R6 M

R4

10 M

C3

NM

4 7

1.IF 11

114

D2

0A90

2

D1=

0490

C4

I

10 µ

F

6

D3

RL

A1N

ik 1

8541

48a

14

IC2

LM38

0N7

3, 4

, 5,

10,1

1,12

R5

100

k

C5

100

nF

\R L

A1

S1

on/o

ff

00/.0

c'JC

61"

1100

81 9VP

P6

Fig

. 54

The

circ

uit d

iagr

am o

f the

Sou

nd-A

ctiV

ated

Sw

itch

RLA

Fig. 55 Constructional details of the Sound -ActivatedSwitch

117



and contacts of adequate rating and correct typeBattery:

B1 PP6 size 9 volt and connector to suitLoudspeaker (microphone):

LS1 Miniature type having an impedance in the range 40 to80 ohms


118

Project 24 - Slide TimerThis project can be used with a projector having a remotecontrol socket to provide automatic slide changing with aninterval between slide changes that is continuously variablebetween approximately 6 and 25 seconds. The unit controlsthe projector via a relay, and it is merely necessary for therelay to be briefly pulsed on at the appropriate frequency. Itis not necessary for the relay to be switched on for the exactlength of time a slide change takes since the automatic slidechange mechanism of projectors have a built-in latching action.It is merely necessary for the relay to be closed long enough tolatch this mechanism.

Refer to Figure 56 for the circuit diagram of the SlideChange Timer, and to Figure 57 for the Verobloc componentlayout and wiring of the unit.

The oscillator is based on IC1 and uses the same configura-tion as that employed in the Metronome project which wasdescribed earlier in this publication. The frequency ofoperation is much lower in this case though, and is set usingVR1 to give slide changes at the required spacing. The relayis driven from the output of IC1 via emitter -follower bufferTr 1 which gives the current amplification needed in order todrive the relay properly. RLA1 is a normally open relaycontact which is used to activate the projector each time therelay is pulsed on.

SKI is connected to the appropriate socket on the pro-jector using a twin lead which does not need to be a screenedtype. It is fitted with a 3.5 mm plug which connects to SK1,and a plug of the appropriate type for the socket on theprojector.

A 4 -pole miniature relay was used for RLA1 in the proto-type Slide Timer unit, and Figure 57 shows a relay having thistype of base. Obviously the wiring to the relay base must bemodified slightly if another type of relay is used, and theretailer's data should give details of the relay's base connec-tions. With a little experimentation and common sense itshould be possible to find the correct method of connectioneven if base connection data is not available.

119

Components for Project 24 - Slide Timer (Fig. 56)Resistors: all 1/3 watt 5%

R1 100 k (brown, black, yellow, gold)R2 100 k (brown, black, yellow, gold)R3 10 k (brown, black, orange, gold)R4 1.8 k (brown, grey, red, gold)

120

1

A BCDEF11-10-1111-0-6

* * s -46-

1*-4*-110-411 aa

2540-0-11-01

Fig. 57 Constructional details of the Slide Timer

121

R5 33 k (orange, orange, orange, gold)VR1 100 k lin. carbon

Capacitor:Cl 33µF 10 V tantalum bead

Semiconductors:IC1 TLO81CPTrl BC109CDI 1N4148D2 1N4148



and contacts of adequate rating and correct typeBattery:

BI PP6 size 9 volt and connector to suitSocket:

SKI 3.5 mm jack socketMiscellaneous:

VeroblocControl knobConnection leadWire

122

Project 25 - Moisture DetectorThis circuit normally produces a low frequency audio outputhaving a fundamental frequency of only a few Hertz, but theoperating frequency rises considerably if a couple of probesare placed in water. A more modest increase in pitch isproduced if the probes are placed in something damp, such asfairly moist soil. In other words the unit acts as a simple formof moisture detector with the rise in pitch corresponding tothe degree of moisture detected. A practical application for aunit such as this is as a soil moisture indicator to show whetheror not a plant needs watering by giving an indication of themoisture at root level.

The circuit diagram of the unit is shown in Figure 58 andthe Verobloc component layout is given in Figure 59.

The circuit is little more than a low frequency oscillatorbased on IC1 and driving loudspeaker LS1 via C2. Thefrequency at which IC1 oscillates can be considerably boostedby switching on Trl so that R3 is effectively connected fromthe input of IC1 to the negative supply rail. As the circuitstands though, Trl is cut off and passes no significant current.

With the probes placed in water there will be a fairly lowresistance between them, and a heavy base current will flowinto Trl so that this device is biased hard into conduction andthe frequency of IC1 is taken to its maximum figure. It shouldperhaps be pointed out that pure water does in fact have avery high resistance, but most sources of water (rain, tapwater, etc.) contain significant amounts of impurities whichproduce a much lower resistance.

If the probes are placed in something that has only amodest moisture content there will be a much higherresistance between them, but Tr 1 will still be biased intoconduction to a certain extent and there will be a significantincrease in the operating frequency of the unit. Thus Trl isnot simply switched fully on or fully off, and intermediatestates (and output frequencies from the unit) can be produced.The probes can simply consist of two pieces of single strandPVC -insulated wire with a small length of insulation (sayabout 5 mm) removed from the ends. If the unit is to be usedas a soil moisture indicator the two probes must be mounted

123

together so that they are a fixed distance apart. A spacing ofabout 20 mm is suitable. The spacing is important as it effectsthe sensitivity of the unit. If the unit seems to be oversensitive,incidentally, removing some of the exposed wire at the end ofeach probe is the easiest way of correcting this. Similarly, alack of sensitivity can be corrected by removing some of theinsulation at the end of each probe to leave a greater length ofexposed wire.

124

1 le- 0111.-A BCDEF GHJKL

11-4-15-11-111

Ilf-111^ 41-1111-11----11-111-1111-411-1111

6-11-111-4M1 7111-41-11-41-111

1* -111-0-111.411

IJ4 r

411

25LSI --{- C2 -i

0-0-0-e- -4%- -------BCDEF GHJK

1

Stblock

Batteryclip

Fig. 59 Constructional details of the Moisture Detector

125

Components for Project 25 - Moisture Detector (Fig. 58)Resistors: all 1/3 watt 5%

RI 100 k (brown, black, yellow, gold)R2 100 k (brown, black, yellow, gold)R3 1 k (brown, black, red, gold)R4 33 k (orange, orange, orange, gold)

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 10 µF 25 V electrolyticC3 100 nF polyester (brown, black, yellow, black, red)

Semiconductors:IC1 LM380NTrl BC109C





VeroblocWire

126

Project 26 - Water Activated MannThis device produces an audible warning sound when water isdetected by a simple sensor. The audio alarm signal is a tonewhich is slowly varied up and down in frequency, and this is avery effective form of alarm signal. Possible applications for aunit of this type include use as a rain alarm or cistern overflowalarm.

Refer to Figure 60 for the complete circuit diagram of theWater Activated Alarm, and to Figure 61 for the Verobloccomponent layout.

The sensor simply consists of two pieces of metal placedvery close together and separated by an insulating material.Thus there is normally an extremely high resistance betweenthe two metal electrodes, but if they are bridged by waterwhich has a significant impurity content there will be a fairlylow resistance between them. Therefore, Tr2 is normally cutoff and passes only minute leakage currents, but if the sensoris activated Tr2 is biased hard into conduction and suppliesvirtually the full supply voltage to the alarm generator circuitwhich is based on ICI and IC2.

IC2 is used as the tone generator and its output is coupledto LS I by C4. The operating frequency of IC2 can be variedup and down by increasing and decreasing the base current fedto Tr 1 . This modulation is provided by IC1 which is used as asimple very low frequency oscillator having an operating fre-quency of only about 0.5 Hertz (i.e. only one cycle every twoseconds).

The output of ICI simply switches straight from the highstate to the low one, and back again, producing a squarewaveoutput. This is not suitable as the modulation signal as itwould simply switch the tone between the frequencies, ratherthan giving the smooth variation in pitch which we requirehere. The signal across C3 is a form of sawtooth waveformwhich steadily rises as C2 charges,and falls as C2 discharges. Itis not actually a linear sawtooth (in other words there is somevariation in the rate at which the voltage rises and falls) butthis is of no consequence here, and it is this signal that is usedto modulate the tone generator. The required loose couplingto the base of Trl is provided by R5.

127

ti 00

R1i

R3

100k

33k

Cl

100

nF

IC1

TL0

81C

P 4 R

4

R2

33 k

RS

100k

T27

M

+C

2

T33

p.F

R6 1k Tr1

BC

109C

C3

elm

10 n

F m

an 4

Fig

. 60

The

circ

uit d

iagr

am o

f the

Wat

er -

Act

ivat

ed A

larm

2

R7

10 k

LM38

0N

3, ,5

,10

,11,

12

R8

18k

10

{11-

C4 pF

40-8

0 Lsi

c(

S1

on/o

ff

(3

Sen

sor

BC

179

B1 9V PP

6ne

s

Batteryclip

+

Fig. 61 Constructional details of the Water -ActivatedAlarm

129

The sensor can simply consist of two non -insulated wiresplaced on a plastic or other insulating base, with the smallestpossible gap between the two wires. Alternatively a small pieceof stripboard or a sensor made from printed circuit boardcould be used.

Components for Project 26 - Water -Activated Alarm (Fig 60)Resistors: all 1/3 watt 5% (10% over 1 M)

R1 100 k (brown, black, yellow, gold)R2 100 k (brown, black, yellow, gold)R3 33 k (orange, orange, orange, gold)R4 33 k (orange, orange, orange, gold)R5 2.7 M (red, violet, green, silver)R6 1 k (brown, black, red, gold)R7 10 k (brown, black, orange, gold)R8 18 k (brown, grey, orange, gold)

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)C2 33 µ F 10 V tantalumC3 10 nF polyester (brown, black, orange, black, red)C4 10 µ F 25 V electrolytic

Semiconductors:ICI TLO81CPIC2 LM380NTrl BC109CTr2 BC179


Loudspeaker.LS1 Miniature type having an impedance in the range 40 to

80 ohmsBattery:


VeroblocSensor (see text)Wire

130

Project 27 - Crystal SetAn obvious advantage of a crystal set over any other type ofreceiver is that it does not require a battery or any other typeof power supply. The power to drive the headphones or ear-phone is derived from the radio signal, but this does give acouple of major disadvantages. One is the need for a fairlylarge aerial since the output from an ordinary ferrite aerial or atelescopic type is nothing like large enough to operate a crystalreceiver. The second disadvantage is that despite the use of alarge aerial to give a strong signal a crystal set is still onlycapable of driving an earphone or headphones, and loudspeakeroperation is not really feasible. Nevertheless, a crystal set is aninteresting project, and is very simple and inexpensive to build.

Figure 62 shows the circuit diagram of a simple medium -waveband crystal receiver, and the Verobloc component layoutfor this is given in Figure 63.

Ll is the aerial coil, and VC1 is the tuning capacitor.Together these form a tuned circuit, and this has a very highimpedance at or close to the resonant frequency, but a lowimpedance at other frequencies. By adjusting VC1 to resonatethe tuned circuit at the frequency of the desired transmissionthis signal is able to pass through to the next stage of thecircuit, but other transmissions which will be on differentfrequencies will be effectively short circuited to earth and thusfiltered out. LI is actually a ferrite aerial, but as stated earlierthis gives an inadequate output for a crystal set and a moreeffective aerial is required. This aerial is simply a fairly longlength of wire, and its output is coupled directly into thetuned circuit. There is a small coupling winding on LI , but thisis not used in this circuit.

The audio signal is modulated onto the RF (radiofrequency) carrier wave by varying the strength of the RFsignal in sympathy with the amplitude of the audio signal(known as amplitude modulation or AM) It is not possible tosimply pass the RF signal through an RF filter to recover theaudio modulation since the positive half cycles will cancel outthe negative half cycles and give an average output voltage ofzero. However, if the RF signal is rectified by a diode and thenRF filtering is used, the cancelling effect is avoided and the

131

average signal level is the same as the audio modulation. Thusthe required audio signal is obtained using this simple methodof demodulation.

In this circuit DI allows positive half -cycles to pass andblocks negative half -cycles. It does not actually matter whichset of half -cycles are used since they are b6th modulated inexactly the same way, and if the polarity of D1 is reversed theset will still function properly. R1 is needed to provide a dis-charge path for the RF filter capacitor, and without RI thiscapacitor would simply charge up to the peak signal level. R1ensures that the smoothed output signal rises and falls insympathy with the average RF signal level so that a properaudio output is obtained. Although the RF filter capacitormay appear to be absent from the circuit, it is in fact pro-vided by the capacitance of the crystal earphone which is fedwith the output signal of the receiver, and no extra filtercapacitance is required.

When building the receiver, either as a permanent unit oron the Verobloc breadboard, keep the aerial coil reasonablyfar away (i.e. at least 20 mm or so) from metal objects or the

Fig. 62 The circuit diagram of the Crystal Set

132

/ coupling winding not used

Ferrite rod

L1

VC1

- 1

ICDEF GH J K M

7

11-1IF - 3

111-111-0-0-411

.

--11-0-0-111 0 P. 11P-411.--111-0-11

I* 19

-0-

T -0-1.---

0- 0-0-0 -IF *

*--116-111.-0 i 0-0-0--0- . 0-41-1111.- ! : INF0-0-0-

A F.',C,DEF- -iGI-IJK',31 --,,, ',II - 0- --iii---p ,

Aerial

Fig. 63 Constructional details of the Crystal Set

SKI

133

performance of the set may suffer. Also, Ll must bepositioned at roughly the right place on the ferrite rod or thecoverage of the set will not be satisfactory. Finding a suitableposition for the coil is simply a matter of trial and error, andany position that permits full coverage of the medium wave-band to be obtained is satisfactory. This is almost certain to bewith the coil almost right at one end of the rod.

The aerial simply consists of a length of insulated wire,and this can be single or multistrand PVC insulated wire, or areasonably thick gauge of enamelled copper wire, say about20 SWG. The wire should be as long as possible, but about 10metres of wire strung around a room should give reasonablereception of a few stations. A longer outdoor aerial will givebetter results, and for optimum results about 20 metres ofwire set as high as possible and clear of buildings and otherlarge obstructions should be used. The wire should not beallowed to come into electrical contact with buildings, trees,or any other object that could leak some of the signal toearth. Performance can be further improved by using an earthconnection, and this can merely consist of a lead attached toa metal pipe which is then buried in the earth about half ametre deep. The lead is then connected to point D-24 on theVerobloc.

Being realistic about it, it is probably not worthwhilespending a great deal of time and money on the installation ofa large aerial and an earth system, and it is probably better justto experiment a little and erect the best aerial that can be pro-duced reasonably easily and at low cost.

Components for Project 27 - Crystal Set (Fig. 62)Resistor:

RI 100 k 1/3 watt 5% (brown, black, yellow, gold)Capacitor:

VC1 300 pF solid dielectric (Jackson Dielecon)Semiconductor:

D1 0A90InductOr:

Ll Denco MW5FR ferrite aerial or similar

134

Socket:SKI 3.5 mm jack socket

Miscellaneous:VeroblocControl knobAerialWireCrystal earpiece

135

Project 28 - Personal MW RadioThis simple receiver gives a level of performance that is similarto that of the crystal set just described, but it uses a ferriteaerial and does not require an external aerial of any kind. Inone respect the performance of the set is superior to that ofthe crystal set, and this is with regard to selectivity. The tuningis not very "sharp" with a crystal set as the aerial and detectorboth reduce the effectiveness of the tuned circuit due toloading effects. This can result in a second station being heardin the background and spoiling reception of the desired station.

Improved results are obtained with this design since there isno external aerial and consequently no loading effects fromthis source. The coupling winding on the aerial coil is used totap off only a relatively small amount of signal from the aerialso that loading is further reduced. A further improvement isobtained by using a technique known as regeneration whichalso boosts the sensitivity of the receiver.

Figure 64 shows the circuit diagram of the receiver, and theVerobloc component layout is given in Figure 65

VC1 and the main winding of LI form the tuned circuit,and the small coupling winding on LI couples the output ofthe aerial to the input of a simple common -emitter amplifierwhich utilizes Tr 1 in a conventional configuration. C2 couplesthe amplified output of Tr 1 to a straightforward diode demo-dulator circuit.

Regeneration is provided by CX which is a very low valuecapacitor which is actually home contructed from a couple ofinsulated wires. This merely sends some of the amplified signalat the collector of Trl back to the aerial so that it is fed backthrough Tr I again for further amplification. This has theobvious effect of boosting the gain of the circuit, but itprovides a greater boost in gain at frequencies where thecircuit is working efficiently than it does at frequencies whereefficiency is poor. In other words, the station to which thereceiver is tuned will be received well as the gain of the set willbe considerably boosted at this frequency, but stations onother frequencies will receive a relatively low boost and theselectivity of the set is thus improved.

One or two points must be borne in mind when constructing

136

this project. One lead from Ll connects direct to VC] and notvia the breadboard. This connection can either be soldered ora crocodile clip can be used. The lead that carries this connec-tion also forms part of CX, and a single -strand insulated leadfrom the breadboard forms the other part of CX (see Figure65). These two leads are twisted together, and up to a pointthe more they are twisted together the better the performanceof the receiver becomes. There is a limit to the boost in per-formance that can be obtained though, and if this limit isexceeded the circuit will oscillate at some settings of thetuning control. This will be heard as a whistling sound thatchanges in pitch as the receiver is tuned through a station, andit makes proper reception impossible. Therefore, CX shouldhave the highest capacitance (the two leads twisted togetheras much as possible) without oscillation occuring at any settingof VC1.

If the receiver is constructed as a permanent project it mustbe housed in a plastic case, or a case made of some other non-metallic substance. A metal case would shield the ferrite aerialfrom radio waves and prevent any signals from being received!

If regeneration cannot be obtained, incidentally, thisprobably means that the phasing of Ll is incorrect and thefeedback through CX is negative rather than positive, and istherefore giving a reduction in performance rather than animprovement. To correct this it is merely necessary to swapover the two leads from Ll's coupling winding so that thecorrect phasing is obtained.

Note that the output of this receiver, and the crystal setdescribed earlier, are only suitable for a crystal earphone. Alow -impedance magnetic type will not give good results withthese designs, and it is unlikely to work at all with them.

Components for Project 28 - Personal MW Radio (Fig. 64)Resistors: all 1/3 watt 5% (10% over 1 M)

R1 1.2 M (brown, red, green, silver)R2 4.7 k (yellow, violet, red, gold)R3 100 k (brown, black, yellow, gold)

Capacitors:Cl 100 nF polyester (brown, black, yellow, black, red)

137

C2 220 nF polyester (red, red, yellow, black, red)C3 10 nF polyester (brown, black, orange, black, red)VC1 300 pF solid dielectric (Jackson Dielecon)

Semiconductors:Trl BC109CDI 0A90D2 0A90

138

*--411

47. DEF CiFiJKL M"; -

Fig. 65 Constructional details of the Personal MW Radio

139


Inductor:LI Denco MW5FR ferrite aerial or similar

Socket:SKI 3.5 mm jack socket


Miscellaneous:VeroblocControl knobCrystal earphoneWire

140

Project 29 - MW RadioThis receiver is simply the one just described but with an audiooutput stage that enables a loudspeaker to be driven at goodvolume. The circuit diagram of the receiver is given in Figure66 and details of the Verobloc component layout are providedin Figure 67.

The circuitry up to the detector stage is exactly the same asthe earlier receiver design, and the only difference in thedetector circuitry is that volume control VR1 is used in placeof the fixed value resistor which was used at this point in theearlier design.

The output stage is a straightforward circuit using theLM380N device. DC blocking capacitor C4 is needed at theinput to IC1 because a small DC potential is developed acrossVR1 when a signal is received, and without C4 this wouldupset the biasing of ICI. C5 is an additional RF filtercapacitor, and this is needed as only a minute RF leakage intoIC1 would be sufficient to make the circuit extremelyunstable. ICI drives a high impedance loudspeaker via C6, andreasonable volume should be obtained from the set. Greatervolume can be obtained using a lower impedance loudspeaker,but 15 ohms is the lowest recommended speaker impedancefor this circuit. In general, the larger the loudspeaker used thegreater the volume level that can be produced.

The constructional and setting -up notes for the previousreceiver also apply to this one, and in addition, if the unit isconstructed as a permanent project, ensure that LS1 and Liare reasonably well separated. Otherwise stray feedback fromthe loudspeaker's coil to Ll could cause poor reception orinstability.

Components for Project 29 - MW Radio (Fig. 66)Resistors: all 1/3 watt 5% (10% over 1 M)

RI 1.2M (brown, red, green, silver)R2 4.7 k (yellow, violet, red, gold)VR1 100 k log. carbon


141

CX

R2

_,4-

7k

Tr1

8C10

9C

C2

0222

0 nF

0490

.11

ICI

14

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111-

-3, 4

, 5

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110

,11,

12

100

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C31

IC

4

C5

3.3

nF

0 nF

100

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01A

0490

Fig

. 66

The

circ

uit d

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MW

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'"100

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7

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81 9V PP

6

Fig. 67 Constructional details of the MW Radio

143

C3 10 nF polyester (brown, black, orange, black, red)C4 100 nF polyester (brown, black, yellow, black, red)C5 3.3 nF ceramicC6 100µF 10 V electrolyticC7 10 nF polyester (brown, black, orange, black, red)C8 100µF 10 V electrolyticVC1 300 pF solid dielectric (Jackson Dielecon)

Semiconductors:TR1 BC109CIC1 LM380ND1 0A90D2 0A90



80 ohms (see text)Inductor:

Ll Denco MW5FR ferrite aerial or similarBattery:


VeroblocControl knobsWire

144

Project 30 - Fuzz UnitThis unit is intended for use with an electric guitar and givesthe well known and popular "fuzz" effect. This effect is oneof the most simple to produce since it merely entails distortingthe signal to produce harmonics (multiples of the fundamentalfrequency). All that is needed in order to achieve this is asimple clipping amplifier such as the one shown in the circuitdiagram of Figure 68 (although there are actually other waysof producing the "fuzz" effect).

Basically the circuit is a high gain inverting amplifier usingoperational amplifier IC1. The gain is set at approximately40 dB (100 times) by feedback resistors R1, R4, and R5. How-ever, if the output of IC1 swings more than about 0.6 voltspositive D2 is biased into conduction and effectively cuts R5out of circuit. The same thing happens if the output of ICIgoes more than about 0.6 volts negative of its quiescent level,except it is D1 that is biased into conduction and bypasses R5.The result of R5 being bypassed is a reduction in the gain ofthe circuit to only about unity. The output from an electricguitar will be quite sufficient to drive the output of ICI to±0.6 volts, even when the signal has decayed from its initialfairly high amplitude. The signal at the output of the unit istherefore subjected to a sudden drop in gain as the ±0.6 voltthreshold level is achieved, giving the required distortion andwhat is virtually a squarewave output.

C2 is used to provide DC blocking at the output, and VR1is the output level control. The latter is needed because theoutput from the Fuzz Unit is considerably stronger than thedirect output from many guitar pick-ups, and VR1 enables theoutput of the Fuzz Unit to be set at about the same level asthe direct output of the pick-up used with the unit.

Figure 69 shows the Verobloc component layout for theFuzz Unit. The input and output of the breadboard can beconnected to 6.35 mm (14 in) jack sockets which in turnconnect to the usual screened jack leads that are used toconnect items of musical equipment to one another. Alterna-tively four short crocodile clip leads can be used to connectthe breadboard to the two jack leads. Of course, the guitarconnects to the input of the unit (SKI) and the output (SK2)

145

oE 0

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CO cocr

Cs!

0 Ct X

CL

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oOcc

1

cr r--Fi 0

QUOC

7 c\i0C

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connects to the input of the guitar amplifier. If there seems tobe a very high level of mains hum this probably means that thetwo leads to SKI. or the two to SK2 are connected around thewrong way. The negative supply rail of the unit (row A)connects to the outer braiding of the input and output leads(the barrels of the jack plugs). The non -earthy input and out-put leads connect to the inner conductors of the jack leads(the tips of the jack plugs).

146

' 1

G L fitD1 +I

Fig. 69 Constructional details of the Fuzz Unit

147

If you construct the unit as a permanent project it is advis-able to use a strong metal case for the unit, and a diecastaluminium type is ideal. This type of case is very tough andgives excellent screening against stray pick-up of mains humand other electrical noise. It is normal for a unit of this type tohave a bypass switch so that the unit can be switched in andout of circuit very easily. If a heavy duty push-button typeswitch is used as the bypass switch, and this is fitted on the lidof the unit, it can be operated by foot while playing the guitarwhich is obviously more convenient than having to use a handoperated type. The bypass switch needs to be a DPDT type,and it is connected in the manner shown in the circuit diagramof Figure 70.

S2oSK1e*

451440-0-C1 VR1

O S2bsNSK2

Fig. 70 Adding a bypass switch to the Fuzz Unit

Components for Project 30 - Fuzz Unit (Fig. 68)Resistors: all 1/3 watt 5% (10% over 1 M)

R1 100 k (brown, black, yellow, gold)R2 4.7 k (yellow, violet, red, gold)R3 4.7 k (yellow, violet, red, gold)R4 100 k (brown, black, yellow, gold)R5 10 M (brown, black, blue, silver)VR1 100 k log. carbon

Capacitors:Cl 220 nF polyester (red, red, yellow, black, red)C2 10 µF 25 V electrolytic

148

Semiconductors:IC 1 TLO81CPDI 1N4148D2 1N4148


Sockets:SKI 6.35 mm standard jack typeSK2 6.35 mm standard jack type



149

Please note overleaf is a list of other titles that are available inour range of Radio, Electronics and Computer Books.

These should be available from all good Booksellers, RadioComponent Dealers and Mail Order Companies.

However, should you experience difficulty in obtaining anytitle in your area, then please write directly to the publisherenclosing payment to cover the cost of the book plus adequatepostage.

If you would like a complete catalogue of our entire rangeof Radio, Electronics and Computer Books then please send aStamped Addressed Envelope to:

BERNARD BABANI (publishing) LTDTHE GRAMPIANS

SHEPHERDS BUSH ROADLONDON W6 7NF

ENGLAND

160 Coil Design and Construction Manual [2.50205 Hi.Fi Loudspeaker Enclosures £2.95208 Practical Stereo &Ouadrophony Handbook £0.75214 Audio Enthusiast's Handbook £0.85219 Solid Slate Novelty Projects £0.85220 Build Your Own Solid State HiFi and Audio Accessories £0.85222 Solid State Short Wave Receivers for Beginners £2.96225 A Practical Introduction to Digital ICs E2.50226 How to Budd Advanced Show Wave Receive,, £2.95227 Beginners Gurde to Building Electronic Projects E1.95228 Essential Theory for the Election., Hobbyist £2.50BP2 Handbook of Radio, TV, Industrial and Transmitting Tube and Vaive Equivalents £0.60BP6 Engineer's & Machinist's Refer... Tables £1.25BP7 Radio & Electronic Colour Codes Data Chart £0.95BP27 Chart of Radio, Electronic, Semiconductor and Logic Symbols £0.95BP28 Resistor Selection Handbook £0.60BP29 Major Solid State Audio H,F i Construction Projects £0.85BP33 Electronic Calculator Users Handbook E1.508P36 50 Circuits Using Germanium Silicon and Zener Diodes E1.508737 50 Projects Usrng Relays, SCRs and TR1ACs E2.95BP39 50 IF ET1 Field Effect Transistor Projects £2.95BP42 50 Simple LED Circuits E1.95BP44 IC 555 Projects £2.958745 Projects in OptoElecbonio £1.95BP48 Electronic Projects for Beginners E1.95BP49 Popular Electronic Projects 42.508P53 Practical Electronics Calculations and Formulae £3.968P54 Your Electronic Calculator & Your Money £1.35BP56 Electronic Security Devices £2.50BP58 50 Circuits Using 7400 Series IC's £2.60BP62 The Simple Electronic Circuit & Components (Elements of Electronics - Book 11 £3.50BP63 Alternating Conant Theory (Elements of Ekctrom. - Book 21 £3.50BP64 Semiconductor Technology (Elements of Electronic - Book 31 £3.60BP66 Beginners Guide to Microprocessors end Computing £1.958P68 Choosing and Using Your Hi-Fi £1.65BP69 Electronic Games E1.75BP70 Transistor Radio Fault.finding Chart £0.95BP72 A Microprocessor Primer £1.75EIP74 Electronic Music Projects £2.50BP76 Power Supply Projects E2.50BP77 Micropropcmg Systems and Circuits (Elements of Electronics - Book 41 £2.96BP78 Practical Computer Experinumb £1.75BP90 Popular Electron. Circuits - Book 1 £2.95BP84 Digital IC Projects £1.95BP85 International Transistor Equivalents Goode £3.50BP86 An Introduction to BASIC Programming Techniques £1.950P8] 50 Simple LED Circuits - Book 2 E1.35131,88 How to Use Op -Amps £2.95BP89 Communication (Elements of Electrons.- Book 51 £2.95BP90 Audio Projects £2.50BP91 An Introduction to Radio DXing E1.95BP92 Electronics Simplified - Crystal Set Construction [1.75BP93 Electronic Timer Projects E1.95BP94 Ebctronic Projects for Cars and Boats E1.95131'95 Model Railway Projects E1.95BPS? IC Projects for Beginners £1.95B1798 Popular Electronic Circuits - Book 2 £2.25BP99 Mini -matrix Board Proiects £2.50BP1O1 How to Identify Unmarked ICs £0.95BP103 Multi -circuit Board Projects £1.95BP104 Electronic Stenos Projects £2.95BP105 Aerial Projects E1.95BP106 Modern Op -amp Projects £1.95BP107 30 Solderless Br/1.60mM Projects - Book 1 £2.25BP108 International Diode Equivalents Guide £2.25BP109 The Art of Programming the 1K 2X81 E1.95BP110 How to Get Your Electronic Projects Working £2.50BP111 Audio (Elements of Electronics - Book 61 £3.50BP112 A Z80 Workshop Manual £3.50BP113 30 Solderless Breadboard Projects - Book 2 £2.25BP114 The An of Programming the 16K ZX81 £2.508P115 The Pre -computer Book E1.95BP117 Practical Electronic Building Blocks - Book 1 £1.958P118 Practical Electronic Building Blaks - Book 2 £1.958P119 The An of Programming the ZX Spectrum £2.50BP120 Audio Amplifier Faultfinding Chart £0.95BP121 How to Design and Make Your Own PCB's £2.508P122 Audio Amplifier Construction £2.25BP123 A Practical Introduction to Illicroproceseors E2.50BP124 Easy Add-on Projects for Spectrum. 2081 & Ace £2.758P125 25 Simple Amateur Band Aerials £1.95BP126 BASIC & PASCAL in Parallel £1.50BP127 How to Design Electronic Projects £2.25BP128 20 Programs for the ZX Spectrum and 16K ZX81 £1.95BP129 An Introduction to Programming the OR IC -1 £1.95BP130 Micro Interfacing Circuits - Book 1 £2.25BP131 Micro Interfacing Circuits - Book 2 £2.75

BP132 25 Simple Shortening Broadcast Bend AerialsBP133 An Introduction to Programming the Dragon 32BP135 Secrets of the Commodore 64BP136 25 Simple Indoor old Window AeriateBP137 BASIC & FORTRAN in ParallelBP138 BASIC & FORTH in ParallelBP139 An Introduction to Programming the BBC Model B MicroBP140 Digital IC &tunalents & Pin ConnectionsBP141 Linear IC Equivalents & Pin ConnectionsBP142 An Introduction to Prograrnmsng the Acorn ElectronBP143 An Introduction to Programming the Atari 600/80051BP144 Further Practical Electronics Cekulations and Formal.BP145 25 Simple Tropical and MW Bend Aerials8P146 The Pre -BASIC BookBP147 An Introduction to 6502 Machine CodeBP148 Computer Terminology ExplainedBP149 A Concise Introduction to the Language of BBC BASICBP152 An Introduction to 280 Machine CodeBP153 An Introduction to Progremming the Amstrad CPC464 andBP154 An Introduction to MSX BASICBP156 An Introduction to 01 Machine CodeBP157 How to Write 20 Spectrum and Spectrum* Gem.. ProgramsBP158 An Introduction to Programming the Commodore 16 and Plus 4BP159 Flow to write Amstrad CPC 464 Games ProgramsEIP161 Into the 01 ArchiveBP162 Counting on 01 Abacus8P169 How to Get Your Computer Programs RunningBP170 An Introduction to Computer PeripheralsBP171 Easy Addon Projects for Amstrad CPC 464. 664. 6128 and MSX ComputersBP173 Computer Music ProjectsBP174 More Advanced Electronic Music ProjectsBP175 How to Write Word Game Pro -warm for the Amstrad CPC 464. 664 and 6123BP176 A TVD/Nrs HandbookBP177 An Introduction to Computer CommunicationsBP179 Electronic Circuits for the Computer Control of RobotsBP180 Electronic Circuits for the Computer Control of Model RailwaysBP181 Getting the Most from Your PrinterBP182 MIDI ProjectsBP183 An Introduction to CP/MBP1B4 An Introduction to 68000 Assembly LanguageBP185 Electronic Synthesiser ConstructionBP1B6 Walkie-Tageie ProjectsBP187 A Practical Reference Guide to Word Processing on the Amstrad PCW8256 & PCW8512SPIN Getting Started with BASIC and LOGO on the Amstrad PCWsBP189 Using Your Arristred CPC Disc DrivesBP190 More Advanced Eleetronk Security ProjectsBP191 Simple Applications of the Amstrad CPC. for Writers0F192 More Advanoed Power Supply ProjectsBP193 LOGO for BeginnersBP194 Modern Opto Device Projects13P195 An Introduction to Satellite TelevisionBP196 BASIC & LOGO in PerellelBP197 An Introduction to the Amstrad PC'sBP196 An Introduction to Antenna TheoryBP199 An Introduction to BASIC -2 on the Amstrad PC'sBP230 An Introduction to GEMBP232 A Concise Introduction to MS.DOSBP233 Electronic Hobbyists HandbookBP234 Transistor Selector GuideBP235 Power Selector GuideBP236 Digital IC Selector Guide -Part 1BP237 DigiNI IC Selector Guide -Part 2BP238 Linear IC Selector GuideBP239 Getting the Most from Your MuttimeterBP240 Remote Control HandbookBP241 An Introduction to 8086 Machine CodeBP242BP243B P244BP245BP246BP247BP248BP249BP250BP251BP252BP253BP254BP255BP256BP257BP258

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664 £2.50£2.50E2.50£2.500.50£2.50£2.50£2.500.50£2.50£3.50E2.95E2.95E2.95£5.9512.95E2.96E2.95£2.95E2.95E2.96£2.95E2.95£2.95E5.95£5.95£2.96E2.95E2.96E2.96E2.96£2.95E5.96£2.96E5.95£2.95£5.95£5.95£295£4.95£495£4.95£4.95E4.96£4.95E2.95E3.95£5.95

An Introduction to Computer Aided Drawing £2.95BBC BASIC86 on the Amstrad PC's end IBM Compatibles - Book 1: Language £3.95BBC BASIC136 on the Amstrad PC's end IBM Compatibles - Book 2: Graphics & Disc Files £3.95Digital Audio Projects £2.95Musicel Applications of the Atari ST's £4.95Moro Advanced MIDI Projects £2.95Test Equipment Corotruction £2.95More Advanced Ten Equipment Construction £2.95Programming in FORTRAN 77 £4.96Computer Hobbyists Handbook £5.95An Introduction to C E2.95Ultra High Power Amplifier Construction £3.95From Atoms to Amperes £2.95International Radio Stations Guide £4.95An Introduction to Loudspeakers end Enclosure Design £2.95An Introduction to Amateur Radio £2.95Learning to Program in C E4.95

BERNARD BP1111

3Breadboard

Projects - Book alA "Solderless Breadboard" is simply a special board on

which electronic circuits can be built and tested. The compon-ents used are just plugged in and unplugged as desired. Apartfrom the obvious advantage of enabling circuit changes to berapidly made when experimenting, it also enables the same com-ponents to be re -used many times over in different projects.

The 30 projects featured in this book have been speciallydesigned to be built on a "Verobloc" breadboard. Whereverpossible the components used are common to several projects,hence with only a modest number of reasonably inexpensivecomponents it is possible to build, in turn, every project shown.

Each project is presented in a similar fashion with a briefcircuit description, circuit diagram, component layout diagram,components list and notes on construction and use wherenecessary.

It would be hoped that even a complete beginner with noprevious knowledge of electronics could successfully constructall the projects in this book with little difficulty.

A companion volume to book number BP113: "30 SOLDELESS BREADBOARD PROJECTS - BOOK 2".

£2.95

ISBN 0-85934-082-1

11 1 V

0 0 2 9 5

9 780859 340823

o // z · contents page chapter 1: using a breadboard 1 components 7 resistors 7 capacitors 9...

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