wireless object locator
TRANSCRIPT
ABSTRACT
An object locator is a device designed to assist its user in finding misplaced household and
personal objects in a home. We probably spend hours every month looking for items around
the home, often in a similar situation. In fact, almost every person in the world suffers this
problem. But now this is not really a big problem because now there’s an inexpensive
gadget to help people quickly find important items by tagging them and using an RF locator
to pinpoint their position in seconds. Advantages of such locators include extensibility and
low maintenance.
In the past few decades, an unprecedented demand for wireless technologies
has been taking place. Mobiles, Laptops, assistants (PDAs), and mobile phones, to name just
a few examples, are becoming part of the everyday life of a growing number of devices that
communicate wirelessly. Radio and infrared (IR) are currently the main parts of the
electromagnetic spectrum used to transmit information wirelessly. IR is becoming more
popular every day and it is being preferred due to its inherent advantages like low power
requirements, security, effective short distance communication as compared to its Radio
counterpart. So we are using this technology in our project.
In this project we aim to design and build a hardware model of IR receiver and simple TV
remote can be used as the transmitter
1
CONTENTS
1.INTRODUCTION …6
2.CIRCUIT DIAGRAM …7
3.COMPONENTS
3.1. Timer IC - NE555 …9
3.2. Transistor - SL 100, BC 148, SK100 …13
3. 3 Diode …14
3.4. Voltage Regulator IC 7805 …19
3.5. Light Emitting Diode …20
3.6. IR receiver ICTK1838 …22
3.7. Dual j-k flipflop-IC4027 …22
3.8. Resistors …24
3.9. Capacitors …26
3.10. 9V,3V Battery …28
3.11 Relay ...29
3.12. Loud speaker …36
4. CIRCUIT OPERATION …37
5. WORKING …39
6. ADVANTAGES …39
7. LIMITATIONS …39
8. FUTURE SCOPE …39
9. REFERENCES …40
2
INTRODUCTION
"Where did I put my car keys?" is a question that we must have heard many times in our
life! How often have you put something down and then spent ages looking for it? Well, our
group decided to invent a gadget that would end this frustration!
The idea was to develop small "tags" that could be clipped onto items which are often
misplaced. These tags would be designed so that if they received a uniquely coded signal
from an IR transmitter, they would emit a bleeping sound. A simple TV remote could be
used to do this.
The idea being, if you are looking for an item which has the tag attached, you could go to
the transmitter and press the associated button. The transmitter would then send out a coded
signal for a specific tag and voila, our item has been located!
An object locator system comprises an activation unit and a remote locator where the remote
locator may be attached to an easily misplaced object, such as a key or key-ring. The
activation unit comprises additional functionality to induce the operator to carry it routinely
so that it might be available at distant sites if needed. In one embodiment, the activation unit
comprises a cellular telephone. In another embodiment, the activation unit comprises a wrist
watch with an integral transmitter. The activation unit, when triggered, generates an
activating signal. The remote locator receives the activating signal and announces its
location. Communication from the activation unit to the remote locator may be direct or
indirect, and may be via radio frequency electromagnetic, optical, or acoustic means. We
can use a simple TV remote as a transmitter
3
CIRCUIT DIAGRAM
4
COMPONENTS LIST
The various components required for implementation of our circuit are listed as follows.
3.1. Timer IC - NE555 …9
3.2. Transistor - SL 100, BC 148, SK100 …13
3. 3 Diode …14
3.4. Voltage Regulator IC 7805 …19
3.5. Light Emitting Diode …20
3.6. IR receiver ICTK1838 …22
3.7. Dual j-k flipflop-IC4027 …22
3.8. Resistors …24
3.9. Capacitors …26
3.10. 9V,3V Battery …28
3.11 Relay ...29
3.12. Loud speaker …36
5
3.1. TIMER IC NE555:
The NE-555 was invented by the Herr. Hans. R. Camenzind in 1970, the NE-555 went on
to become a legend in the Electronics industry, the chip possibly deriving its "nick-name"
from the three 5K resistors, R7, R8 and R9, all of which form the very unique " five - five -
five " resistor combination. The standard NE-555 can be a stand-alone compact device, yet
powerful enough to perform basic timing functions or as a versatile timer or even as a
simple oscillator to create tones of various pitches up to the ultrasonic’s of 200KHz.
Pin Diagram :
Pin Description :
The connection of the pins is as follows:
Pin Name Purpose
1 GND Ground, low level (0 V)
2 TRIG OUT rises, and interval starts, when this input falls below 1/3 VCC.
3 OUT This output is driven to +VCC or GND.
4 RESET A timing interval may be interrupted by driving this input to GND.
5 CTRL "Control" access to the internal voltage divider (by default, 2/3 VCC).
6 THR The interval ends when the voltage at THR is greater than at CTRL.
7 DIS Open collector output; may discharge a capacitor between intervals.
8 V+, VCC Positive supply voltage is usually between 3 and 15 V.
6
The NE-555, in figure above is supplied in a plastic package 8 pin DIP (Dual IN-Line
package). The NE-556 timer is a dual version of the NE-555 and comes in a standard 14-pin
DIP plastic package, with two NE - 555 timers within. The NE-558 was a quad version of
the NE-555with four distinct NE-555's within the one package, incidentally in a 14 pin DIP
case, however it was scheduled to be discontinued due to its lack of popularity and also
more importantly, its own inherent internal "noise" problems.
IC NE555:
The 555 monolithic timing circuit is a highly stable controller capable of
producing accurate time delays or oscillations.
Features:
Turn off time less than 2μs
Max operating frequency greater than 500 kHz.
Output can source and sink currents up to 200 mA.
Timing from microseconds to hours.
Basic NE-555 One-Shot ( Monostable ) Operation:
A monostable circuit produces a single output pulse when triggered. It is called a
monostable because it is stable in just one state: 'output low'. The 'output high' state is
temporary.
The duration of the pulse is called the time period (T) and this is determined by resistor R1
and capacitor C1:
Time period, T = 1.1 × R1 × C1
T = time period in seconds (s)
R1 = resistance in ohms ( )
C1 = capacitance in farads (F)
The time period is multiplied by 1.1 because, the capacitor charges to 2/3 = 67% so it is a bit
longer than the time constant (R1 × C1) which is the time taken to charge to 63%.
7
555 monostable output, a single pulse:
555 monostable circuit with manual trigger:
Monostable operation:
The timing period is triggered (started) when the trigger input (555 pin 2) is less than 1/3 Vs,
this makes the output high (+Vs) and the capacitor C1 starts to charge through resistor R1.
Once thetime period has started further trigger pulses are ignored.
The threshold input (555 pin 6) monitors the voltage across C1 and when this reaches 2/3 Vs
the time period is over and the output becomes low. At the same time discharge (555 pin 7)
is connected to 0V, discharging the capacitor ready for the next trigger.
8
The reset input (555 pin 4) overrides all other inputs and the timing may be cancelled at any
time by
connecting
reset to 0V, this
instantly
makes the output
low and
discharges
the capacitor.
If the reset
function is
not required the reset pin should be connected to +Vs.
Applications :
In the monostable mode, the 555 functions as a "one-shot". Applications include timers,
missing pulse detection, bounce free switches, touch switches, frequency divider,
capacitance measurement, pulse-width modulation (PWM) etc
9
3.2. TRANSISTOR – SL 100, BC 148, SK100:
The SL 100 and BC148 are a general purpose silicon, NPN, bipolar junction transistors .SK
100 is a PNP transistor .If the T0-92 package is held in front of one's face with the flat side
facing toward you and the leads downward, the order of the leads, from left to right is
collector, base, emitter.
SL100 - NPN - 50V 500Ma:
SL 100 is an low power NPN transistor.
10
3.3 SEMICONDUCTOR DIODES
Figure 7: Typical diode packages in same alignment as diode symbol. Thin bar depicts
thecathode.
A modern semiconductor diode is made of a crystal of semiconductor like silicon that has
impurities added to it to create a region on one side that contains negative charge
carriers(electrons), called n-type semiconductor, and a region on the other side that contains
positive charge carriers (holes), called p-type semiconductor. The diode's terminals are
attached to each of these regions. The boundary within the crystal between these two
regions, called aPN junction, is where the action of the diode takes place. The crystal
conducts conventional current in a direction from the p-type side (called the anode) to the n-
type side (called thecathode), but not in the opposite direction.
Another type of semiconductor diode, the Schottky diode, is formed from the contact
between a metal and a semiconductor rather than by a p-n junction.
11
Current–voltage characteristic
A semiconductor diode’s behavior in a circuit is given by its current–voltage characteristic,
or I–V graph (see graph below). The shape of the curve is determined by the transport of
charge carriers through the so-called depletion layer or depletion region that exists at the p-n
junctionbetween differing semiconductors. When a p-n junction is first created, conduction
band (mobile) electrons from the N-doped region diffuse into the P-doped region where
there is a large population of holes (vacant places for electrons) with which the electrons
“recombine”. When a mobile electron recombines with a hole, both hole and electron
vanish, leaving behind an immobile positively charged donor (dopant) on the N-side and
negatively charged acceptor (dopant) on the P-side. The region around the p-n junction
becomes depleted of charge carriers and thus behaves as an insulator.
However, the width of the depletion region (called the depletion width) cannot grow without
limit. For each electron-hole pair that recombines, a positively charged dopant ion is left
behind in the N-doped region, and a negatively charged dopant ion is left behind in the P-
doped region. As recombination proceeds more ions are created, an increasing electric field
develops through the depletion zone which acts to slow and then finally stop recombination.
At this point, there is a “built-in” potential across the depletion zone.
If an external voltage is placed across the diode with the same polarity as the built-in
potential, the depletion zone continues to act as an insulator, preventing any significant
electric current flow (unless electron/hole pairs are actively being created in the junction by,
for instance, light. see photodiode). This is the reverse bias phenomenon. However, if the
polarity of the external voltage opposes the built-in potential, recombination can once again
proceed, resulting in substantial electric current through the p-n junction (i.e. substantial
numbers of electrons and holes recombine at the junction). For silicon diodes, the built-in
potential is approximately 0.7 V (0.3 V for Germanium and 0.2 V for Schottky). Thus, if an
external current is passed through the diode, about 0.7 V will be developed across the diode
such that the P-doped region is positive with respect to the N-doped region and the diode is
said to be “turned on” as it has a forward bias.
A diode’s 'I–V characteristic' can be approximated by four regions of operation.
12
Figure 5: I–V characteristics of a P-N junction diode (not to scale).
At very large reverse bias , beyond the peak inverse voltage or PIV, a process called
reverse breakdown occurs which causes a large increase in current (i.e. a large number of
electrons and holes are created at, and move away from the pn junction) that usually
damages the device permanently. The avalanche diode is deliberately designed for use in the
avalanche region. In the zener diode, the concept of PIV is not applicable. A zener diode
contains a heavily doped p-n junction allowing electrons to tunnel from the valence band of
the p-type material to the conduction band of the n-type material, such that the reverse
voltage is “clamped” to a known value (called the zener voltage), and avalanche does not
occur. Both devices, however, do have a limit to the maximum current and power in the
clamped reverse voltage region. Also, following the end of forward conduction in any diode,
there is reverse current for a short time. The device does not attain its full blocking
capability until the reverse current ceases.
The second region, at reverse biases more positive than the PIV, has only a very small
reverse saturation current. In the reverse bias region for a normal P-N rectifier diode, the
current through the device is very low (in the µA range). However, this is temperature
dependent, and at sufficiently high temperatures, a substantial amount of reverse current can
be observed (mA or more).
13
The third region is forward but small bias, where only a small forward current is conducted.
As the potential difference is increased above an arbitrarily defined “cut-in voltage” or “on-
voltage” or “diode forward voltage drop (Vd)”, the diode current becomes appreciable (the
level of current considered “appreciable” and the value of cut-in voltage depends on the
application), and the diode presents a very low resistance. The current–voltage curve
is exponential. In a normal silicon diode at rated currents, the arbitrary “cut-in” voltage is
defined as 0.6 to 0.7 volts. The value is different for other diode types — Schottky
diodes can be rated as low as 0.2 V, Germanium diodes 0.25-0.3 V, and red or blue light-
emitting diodes (LEDs) can have values of 1.4 V and 4.0 V respectively.
At higher currents the forward voltage drop of the diode increases. A drop of 1 V to 1.5 V is
typical at full rated current for power diodes.
Shockley diode equation
The Shockley ideal diode equation or the diode law (named after transistor co-
inventor William Bradford Shockley, not to be confused withtetrode inventor Walter H.
Schottky) gives the I–V characteristic of an ideal diode in either forward or reverse bias (or
no bias). The equation is:
where
I is the diode current,
IS is the reverse bias saturation current (or scale current),
VD is the voltage across the diode,
VT is the thermal voltage, and
n is the ideality factor, also known as the quality factor or sometimes emission
coefficient. The ideality factor n varies from 1 to 2 depending on the fabrication
process and semiconductor material and in many cases is assumed to be
approximately equal to 1 (thus the notation n is omitted).
14
The thermal voltage VT is approximately 25.85 mV at 300 K, a temperature close to
“room temperature” commonly used in device simulation software. At any temperature it is
a known constant defined by:
where k is the Boltzmann constant, T is the absolute temperature of the p-n junction,
and q is the magnitude of charge on an electron (theelementary charge).
The Shockley ideal diode equation or the diode law is derived with the assumption that the
only processes giving rise to the current in the diode are drift (due to electrical field),
diffusion, and thermal recombination-generation. It also assumes that the recombination-
generation (R-G) current in the depletion region is insignificant. This means that the
Shockley equation doesn’t account for the processes involved in reverse breakdown and
photon-assisted R-G. Additionally, it doesn’t describe the “leveling off” of the I–V curve at
high forward bias due to internal resistance.
Under reverse bias voltages (see Figure 5) the exponential in the diode equation is
negligible, and the current is a constant (negative) reverse current value of −IS. The
reverse breakdown region is not modeled by the Shockley diode equation.
For even rather small forward bias voltages (see Figure 5) the exponential is very large
because the thermal voltage is very small, so the subtracted ‘1’ in the diode equation is
negligible and the forward diode current is often approximated as
The use of the diode equation in circuit problems is illustrated in the article on diode
modeling.
15
3.4VOLTAGE REGULATOR IC 7805:
7805 5V Integrated Circuit 3–Terminal Positive Voltage Regulator
A voltage regulator generates a fixed output voltage of a preset magnitude that remains
constant regardless of changes to its input voltage or load conditions. There are two types of
voltage regulators: linear and switching.
A linear regulator employs an active (BJT or MOSFET) pass device (series or shunt)
controlled by a high gain differential amplifier. It compares the output voltage with a precise
reference voltage and adjusts the pass device to maintain a constant output voltage.
A switching regulator converts the dc input voltage to a switched voltage applied to a power
MOSFET or BJT switch. The filtered power switch output voltage is fed back to a circuit
that controls the power switch on and off times so that the output voltage remains constant
regardless of input voltage or load current changes.
The 7805 fixed voltage regulator is a monolithic integrated circuit in a TO220 type package
designed for use in a wide variety of applications including local, onboard regulation. This
regulator employs internal current limiting, thermal shutdown, and safe area compensation.
With adequate heat-sinking it can deliver output currents in excess of 1.0 ampere. Although
designed primarily as a fixed voltage regulator, this device can be used with external
components to obtain adjustable voltages and currents.
16
3.5 LED
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator
lamps in many devices, and are increasingly used for lighting. Introduced as a practical
electronic component in 1962,[2] early LEDs emitted low-intensity red light, but modern
versions are available across the visible, ultraviolet and infrared wavelengths, with very high
brightness.
When a light-emitting diode is forward biased (switched on), electrons are able
to recombine with electron holes within the device, releasing energy in the form of photons.
This effect is called electroluminescence and the color of the light (corresponding to the
energy of the photon) is determined by the energy gap of the semiconductor. An LED is
often small in area (less than 1 mm2), and integrated optical components may be used to
shape its radiation pattern. LEDs present many advantages over incandescent light sources
including lower energy consumption, longer lifetime, improved robustness, smaller size,
faster switching, and greater durability and reliability. LEDs powerful enough for room
lighting are relatively expensive and require more precise current and heat management than
compact fluorescent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as replacements for lighting,
automotive (particularly brake lamps, turn signals and indicators)
17
3.6 IR RECEIVER-IC TK1838:
Detects burst frequency generated by an IR transmitter.
Features:
High immunity against ambient light.
Low power consumption.
High sensitivity.
Continuous transmission possible
3.7 IC CD4027
It is a dual J-K Master/Slave flip flop with set and reset.
The JK flip-flop augments the behavior of the SR flip-flop (J=Set, K=Reset) by interpreting
the S = R = 1 condition as a "flip" or toggle command. Specifically, the combination J = 1,
K = 0 is a command to set the flip-flop; the combination J = 0, K = 1 is a command to reset
the flip-flop; and the combination J = K = 1 is a command to toggle the flip-flop, i.e.,
change its output to the logical complement of its current value. Setting J = K = 0 does NOT
result in a D flip-flop, but rather, will hold the current state. To synthesize a D flip-flop,
simply set K equal to the complement of J. The JK flip-flop is therefore a universal flip-flop,
because it can be configured to work as an SR flip-flop, a D flip-flop, or a T flip-flop.
NOTE: The flip-flop is positive-edge triggered (rising clock pulse) as seen in the timing
diagram.
18
A circuit symbol for a Positive edge triggered JK flip-flop, where > is the clock input, J
and K are data inputs, Q is the stored data output, and Q' is the inverse of Q
The characteristic equation of the JK flip-flop is:
and the corresponding truth table is:
JK Flip Flop operation
Characteristic table Excitation table
J K Qnext Comment Q Qnext J K Comment
0 0 Qprev hold state 0 0 0 X No change
0 1 0 reset 0 1 1 X Set
1 0 1 set 1 0 X 1 Reset
1 1 Qprev toggle 1 1 X 0 No change
19
JK flip-flop
JK flip-flop timing diagram
Features:
Wide supply voltage range
High noise immunity
Low power
20
RESISTOR :
A resistor is a two-terminal electronic component that produces a voltage across its
terminals that is proportional to the electric current through it in accordance with Ohm's law:
V = IR
A resistor restricts the flow of current. Resistors are elements of electrical networks and
electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be
made of various compounds and films, as well as resistance wire .The primary
characteristics of a resistor are the resistance, the tolerance, the maximum working voltage
and the power rating. Other characteristics include temperature coefficient, noise, and
inductance.
Units of resistance :
The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm.
Symbol of resistance :
Resistor color coding :
Resistor values are normally shown using colored bands. Each color represents a number as
shown in the table.
Most resistors have 4 bands:
The first band gives the first digit.
The second band gives the second digit.
The third band indicates the number of zeros.
The fourth band is used to shows the tolerance (precision) of the resistor, this may be
ignored for almost all circuits.
21
Electrical energy is converted to heat when current flows through a resistor.
Usually the effect is negligible, but if the resistance is low (or the voltage across the resistor
high) a large current may pass making the resistor become noticeably warm. The resistor
must be able to withstand the heating effect and resistors have power ratings to show this.
The power, P, developed in a resistor is given by:
P = I² × R
or
P = V² / R
where: P = power developed in the resistor in watts (W)
I = current through the resistor in amps (A)
R = resistance of the resistor in ohms ( )
V = voltage across the resistor in volts (V)
Every resistor falls into one of two categories: fixed or variable. A fixed resistor has a
predetermined amount of resistance to current, while a variable resistor can be adjusted to
give different levels of resistance. Variable resistors are also called potentiometers and are
commonly used as volume controls on audio devices. A rheostat is a variable resistor made
specifically for use with high currents. There are also thermisters which either raise or lower
resistance when temperature rises or drops; and light-sensitive resistors wer ratings of
resistors:
3.9.CAPACITOR :
22
A capacitor is a passive electronic component consisting of a pair of conductors separated
by a dielectric (insulator). When there is a potential difference (voltage) across the
conductors, a static electric field develops in the dielectric that stores energy and produces a
mechanical force between the conductors. An ideal capacitor is characterized by a single
constant value, capacitance, measured in farads. This is the ratio of the electric charge on
each conductor to the potential difference between them. Capacitors store electric charges.
Capacitors are widely used in electronic circuits for blocking direct current while allowing
alternating current to pass, in filter networks, for smoothing the output of power supplies, in
the resonant circuits that tune radios to particular frequencies and for many other purposes.
The effect is greatest when there is a narrow separation between large areas of conductor,
hence capacitor conductors are often called "plates", referring to an early means of
construction. In practice the dielectric between the plates passes a small amount of leakage
current and also has an electric field strength limit, resulting in a breakdown voltage, while
the conductors and leads introduce an undesired inductance and resistance.
Operation :
A capacitor consists of two conductors separated by a non-conductive region called the
dielectric medium though it may be a vacuum or a semiconductor depletion region
chemically identical to the conductors. A capacitor is assumed to be self-contained and
isolated, with no net electric charge and no influence from any external electric field. The
conductors thus hold equal and opposite charges on their facing surfaces and the dielectric
develops an electric field. In SI units, a capacitance of one farad means that one coulomb of
charge on each conductor causes a voltage of one volt across the device.
The capacitor is a reasonably general model for electric fields within electric circuits. An
ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of
charge ±Q on each conductor to the voltage V between them. C = Q / V
Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to
vary. In this case, capacitance is defined in terms of incremental changes:
C = dq / dv.
23
Energy storage:
Work must be done by an external influence to "move" charge between the conductors in a
capacitor. When the external influence is removed the charge separation persists in the
electric field and energy is stored to be released when the charge is allowed to return to its
equilibrium position.
The work done in establishing the electric field, and hence the amount of energy stored, is
given by:
W = 1 / 2 CV2
Current-voltage relation:
The current i(t) through any component in an electric circuit is defined as the rate of flow of
a charge q(t) passing through it, but actual charges, electrons, cannot pass through the
dielectric layer of a capacitor, rather an electron accumulates on the negative plate for each
one that leaves the positive plate, resulting in an electron depletion and consequent positive
charge on one electrode that is equal and opposite to the accumulated negative charge on the
other. Thus the charge on the electrodes is equal to the integral of the current as well as
proportional to the voltage as discussed above. As with any antiderivative, a constant of
integration is added to represent the initial voltage v (t0). This is the integral form of the
capacitor equation.
v(t) =1 / C * ∫ i(t) dt
Taking the derivative of this, and multiplying by C, yields the derivative form,
i(t) = C * dv /dt
The dual of the capacitor is the inductor, which stores energy in the magnetic field rather
than the electric field. Its current-voltage relation is obtained by exchanging current and
voltage in the capacitor equations and replacing C with the inductance L.
Capacitor symbol :
24
Examples : Circuit symbols :
Capacitor markings:
Most capacitors have numbers printed on their bodies to indicate their electrical
characteristics. Larger capacitors like electrolytic usually display the actual capacitance
together with the unit (for example, 220 μF). Smaller capacitors like ceramics, however, use
a shorthand consisting of three numbers and a letter, where the numbers show the
capacitance in pF (calculated as XY x 10Z for the numbers XYZ) and the letter indicates the
tolerance (J, K or M for ±5%, ±10% and ±20% respectively).
Additionally, the capacitor may show its working voltage, temperature and other relevant
characteristics.
Example :
A capacitor with the text 473K 330V on its body has a capacitance of 47 x 103 pF = 47 nF
(±10%) with a working voltage of 330 V.
Applications:
Capacitors have many uses in electronic and electrical systems. They are so common that it
is a rare electrical product that does not include at least one for some purpose.
3.10. 9V BATTERY:
25
An electrical battery is one or more electrochemical cells that convert stored chemical
energy into electrical energy. Since the invention of the first battery (or "voltaic pile") in
1800 by Alessandro Volta, batteries have become a common power source for many
household and industrial applications.
There are two types of batteries: primary batteries (disposable batteries), which are
designed to be used once and discarded, and secondary batteries (rechargeable batteries),
which are designed to be recharged and used multiple times. Miniature cells are used to
power devices such as hearing aids and wristwatches; larger batteries provide standby power
for telephone exchanges or computer data centers.
Symbol :
3.11 RELAY:
A relay is an electrically operated switch. Many relays use an electromagnet to operate a
switching mechanism mechanically, but other operating principles are also used. Relays are
used where it is necessary to control a circuit by a low-power signal (with complete
electrical isolation between control and controlled circuits), or where several circuits must
be controlled by one signal. The first relays were used in long distance telegraph circuits,
repeating the signal coming in from one circuit and re-transmitting it to another. Relays
were used extensively in telephone exchanges and early computers to perform logical
operations.
A type of relay that can handle the high power required to directly drive an electric motor is
called a contactor. Solid-state relays control power circuits with no moving parts, instead
using a semiconductor device to perform switching. Relays with calibrated operating
26
characteristics and sometimes multiple operating coils are used to protect electrical circuits
from overload or faults; in modern electric power systems these functions are performed by
digital instruments still called "protective relays".
Basic design and operation
Simple electromechanical relay
A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron yoke
which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more
sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke and
mechanically linked to one or more sets of moving contacts. It is held in place by a spring so that
when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the
two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have
more or fewer sets of contacts depending on their function. The relay in the picture also has a wire
connecting the armature to the yoke. This ensures continuity of the circuit between the moving
contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which
is soldered to the PCB.
When an electric current is passed through the coil it generates a magnetic field that attracts
the armature, and the consequent movement of the movable contact(s) either makes or
breaks (depending upon construction) a connection with a fixed contact. If the set of
contacts was closed when the relay was de-energized, then the movement opens the contacts
and breaks the connection, and vice versa if the contacts were open. When the current to the
coil is switched off, the armature is returned by a force, approximately half as strong as the
magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity
is also used commonly in industrial motor starters. Most relays are manufactured to operate
27
quickly. In a low-voltage application this reduces noise; in a high voltage or current
application it reduces arcing.
Types
Latching relay
A latching relay has two relaxed states (bistable). These are also called "impulse", "keep", or
"stay" relays. When the current is switched off, the relay remains in its last state. This is
achieved with a solenoid operating a ratchet and cam mechanism, or by having two
opposing coils with an over-center spring or permanent magnet to hold the armature and
contacts in position while the coil is relaxed, or with a remanent core. In the ratchet and cam
example, the first pulse to the coil turns the relay on and the second pulse turns it off. In the
two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns
the relay off. This type of relay has the advantage that it consumes power only for an
instant, while it is being switched, and it retains its last setting across a power outage. A
remanent core latching relay requires a current pulse of opposite polarity to make it change
state.
Reed relay
A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts inside
an evacuated or inert gas-filled glass tube which protects the contacts against
atmospheric corrosion; the contacts are made of magnetic material that makes them move
under the influence of the field of the enclosing solenoid. Reed relays can switch faster than
larger relays, require only little power from the control circuit, but have low switching
current and voltage ratings.
Mercury-wetted relay
A mercury-wetted reed relay is a form of reed relay in which the contacts are wetted with
mercury. Such relays are used to switch low-voltage signals (one volt or less) where the
mercury reduces the contact resistance and associated voltage drop, for low-current signals
where surface contamination may make for a poor contact, or for high-speed applications
where the mercury eliminates contact bounce. Mercury wetted relays are position-sensitive
28
and must be mounted vertically to work properly. Because of the toxicity and expense of
liquid mercury, these relays are now rarely used. See also mercury switch.
Polarized relay
A polarized relay placed the armature between the poles of a permanent magnet to increase
sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect
faint pulses and correct telegraphic distortion. The poles were on screws, so a technician
could first adjust them for maximum sensitivity and then apply a bias spring to set the
critical current that would operate the relay.
Machine tool relay
A machine tool relay is a type standardized for industrial control of machine tools, transfer
machines, and other sequential control. They are characterized by a large number of contacts
(sometimes extendable in the field) which are easily converted from normally-open to
normally-closed status, easily replaceable coils, and a form factor that allows compactly
installing many relays in a control panel. Although such relays once were the backbone of
automation in such industries as automobile assembly, the programmable logic
controller (PLC) mostly displaced the machine tool relay from sequential control
applications.
Contactor relay
A contactor is a very heavy-duty relay used for switching electric motors and lighting
loads, although contactors are not generally called relays. Continuous current ratings for
common contactors range from 10 amps to several hundred amps. High-current contacts are
made with alloys containing silver. The unavoidable arcing causes the contacts to oxidize;
however, silver oxide is still a good conductor.Such devices are often used for motor
starters. A motor starter is a contactor with overload protection devices attached. The
overload sensing devices are a form of heat operated relay where a coil heats a bi-metal
strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These
auxiliary contacts are in series with the coil. If the overload senses excess current in the
load, the coil is de-energized. Contactor relays can be extremely loud to operate, making
them unfit for use where noise is a chief concern.
29
A solid state relay (SSR) is a solid state electronic component that provides a similar
function to an electromechanical relay but does not have any moving components,
increasing long-term reliability. With early SSR's, the tradeoff came from the fact that every
transistor has a small voltage drop across it. This voltage drop limited the amount of current
a given SSR could handle. As transistors improved, higher current SSR's, able to handle 100
to 1,200 Amperes, have become commercially available. Compared to electromagnetic
relays, they may be falsely triggered by transients.
Solid state contactor relay
A solid state contactor is a heavy-duty solid state relay, including the necessary heat sink,
used for switching electric heaters, small electric motors and lighting loads; where frequent
on/off cycles are required. There are no moving parts to wear out and there is no contact
bounce due to vibration. They are activated by AC control signals or DC control signals
from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources,
or other microprocessor and microcontroller controls.
Buchholz relay
A Buchholz relay is a safety device sensing the accumulation of gas in large oil-
filledtransformers, which will alarm on slow accumulation of gas or shut down the
transformer if gas is produced rapidly in the transformer oil.
Forced-guided contacts relay
A forced-guided contacts relay has relay contacts that are mechanically linked together, so
that when the relay coil is energized or de-energized, all of the linked contacts move
together. If one set of contacts in the relay becomes immobilized, no other contact of the
same relay will be able to move. The function of forced-guided contacts is to enable the
safety circuit to check the status of the relay. Forced-guided contacts are also known as
"positive-guided contacts", "captive contacts", "locked contacts", or "safety relays".
Overload protection relay
Electric motors need overcurrent protection to prevent damage from over-loading the motor,
or to protect against short circuits in connecting cables or internal faults in the motor
windings. One type of electric motor overload protection relay is operated by a heating
30
element in series with the electric motor. The heat generated by the motor current heats
a bimetallic strip or melts solder, releasing a spring to operate contacts. Where the overload
relay is exposed to the same environment as the motor, a useful though crude compensation
for motor ambient temperature is provided.
Pole and throw
Circuit symbols of relays. (C denotes the common terminal in SPDT and DPDT types.)
File:Relaycov.jpg
The diagram on the package of a DPDT AC coil relay
Since relays are switches, the terminology applied to switches is also applied to relays. A
relay will switch one or more poles, each of whose contacts can be thrown by energizing the
coil in one of three ways:
Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit
is disconnected when the relay is inactive. It is also called a Form A contact or "make"
contact. NOcontacts can also be distinguished as "early-make" or NOEM, which means
that the contacts will close before the button or switch is fully engaged.
31
Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the
circuit is connected when the relay is inactive. It is also called a Form B contact or
"break" contact. NCcontacts can also be distinguished as "late-break" or NCLB, which
means that the contacts will stay closed until the button or switch is fully disengaged.
Change-over (CO), or double-throw (DT), contacts control two circuits: one normally-
open contact and one normally-closed contact with a common terminal. It is also called
a Form C contact or "transfer" contact ("break before make"). If this type of contact
utilizes a "make before break" functionality, then it is called a Form D contact.
The following designations are commonly encountered:
SPST – Single Pole Single Throw. These have two terminals which can be connected or
disconnected. Including two for the coil, such a relay has four terminals in total. It is
ambiguous whether the pole is normally open or normally closed. The terminology
"SPNO" and "SPNC" is sometimes used to resolve the ambiguity.
SPDT – Single Pole Double Throw. A common terminal connects to either of two
others. Including two for the coil, such a relay has five terminals in total.
DPST – Double Pole Single Throw. These have two pairs of terminals. Equivalent to
two SPST switches or relays actuated by a single coil. Including two for the coil, such a
relay has six terminals in total. The poles may be Form A or Form B (or one of each).
DPDT – Double Pole Double Throw. These have two rows of change-over terminals.
Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has
eight terminals, including the coil.
The "S" or "D" may be replaced with a number, indicating multiple switches connected to a
single actuator. For example 4PDT indicates a four pole double throw relay (with 14
terminals).
EN 50005 are among applicable standards for relay terminal numbering; a typical EN
50005-compliant SPDT relay's terminals would be numbered 11, 12, 14, A1 and A2 for the
C, NC, NO, and coil connections, respectively
Relay:
A relay is an electrically operated switch. Current flowing through the
32
coil of the relay creates a magnetic field which attracts a lever and changes the
switch contacts.
Features:
Relays can switch AC and DC.
Relays can switch high voltages.
Relays are a better choice for switching large currents (> 5A).
Relays can switch many contacts at once
3.12. Loud speaker:
A loudspeaker (or "speaker") is an electro-acoustic transducer that converts an electrical
signal into sound. The speaker moves in accordance with the variations of an electrical
signal and causes sound waves to propagate through a medium such as air or water.
33
CIRCUIT OPERATION
The IC’s NE555, CD4027 and the IR sensor TK1838 get the supply voltage from IC 7805
which in turn gets the supply from the 9V battery. The capacitor C1 which is connected
between the output terminal and common terminal (i.e. gnd) of the IC LM7805 is used to
improve the transient response and the out put impedance.
The output of IR sensor TK1838 is normally high. It responds to a frequency of
38khz.When it detects IR light of appropriate frequency the output goes low. The capacitor
C5 is connected to avoid noise and false triggering.
The timer IC NE555 is used in monostable mode of operation. The timing period is
triggered (started) when the trigger input (555 pin 2) is less than 1/3 VCC, this makes the
output high (+VCC) and the capacitor C2 starts to charge through resistor R2. Once the time
period has started further trigger pulses are ignored. The threshold input (555 pin 6)
monitors the voltage across C2 and when this reaches 2/3 VCC the time period is over and the
output becomes low. At the same time discharge (555 pin 7) is connected to 0V, discharging
the capacitor ready for the next trigger. The reset input (555 pin 4) overrides all other inputs
this instantly makes the output low and discharges the capacitor. The reset function is not
required, hence the reset pin is connected to +VCC.
Output of the IR sensor acts as a trigger for the timer IC .The resistance R2 (100k) and
capacitance C2 (10μF) determine the ON time of the IC which is given by:-
TON=1.1RC
Therefore the ON time is 1.1 second .The capacitor C4 is connected to ground noise pickup
while the combination of R3, C3 is used to avoid false triggering of the monostable
NE555.The IC CD4027 is a Dual J-K Master/Slave flip flop. Each flip flop has independent
J, K, Set, Reset and clock inputs. These flip-flops are edge sensitive to the clock input and
change state on the positive-going transition of the clock pulse. Set and reset are
34
independent of the clock (grounded in this case). The J-K flip-flop is used in the toggle
mode. Both the J and K terminals are connected to VCC.
Relays allow one circuit to switch a second circuit which can be completely separate from
the first. There is no electrical connection inside the relay between the two circuits, the link
is magnetic and mechanical. The relay RL1 is 9V, 100Ω SPDT (i.e. Single Pole Double
Throw) switch. The current requirement for the relay is given by (Voltage rating)/ (Coil
Resistance). In this case the current requirement is 90mA.
Back-EMF diode 1N4007 is connected across the relay for the protection of transistors and
IC’s from the brief high voltage spike produced when the relay is switched off. Diode is
connected 'backwards' so that it will normally not conduct. Conduction only occurs when
the relay coil is switched off, at this moment current tries to continue flowing through the
coil and it is harmlessly diverted through the diode. Without the diode no current could flow
and the coil would produce a damaging high voltage 'spike' in its attempt to keep the current
flowing.
SL 100 is an npn transistor enclosed in a metal casing (better heat dissipation) and is
used in a open collector mode. The output current of the J-K flip-flop is low (0.88 mA at 25˚
C) which is much less than that required by the relay, SL 100 is used to amplify the current.
LED2, LED3, and LED4 are used to display the status of each output stage during circuit
operation.
35
WORKING:
The IR sensor detects the IR light from the transmitter and its output goes low.
This acts as a trigger for the timer IC555 which is used in the monostable mode of
operation. The output of the timer IC goes high.
This toggles the J-K flip flop, whose Q output drives the relay through SL100 npn
transistor
The second part of the circuit is basically a two-stage amplifier with a feedback
arrangement.when the loop is connected the base of the T1 is shorted to its
emitter.Hence the base current cease to flow and the circuit doed bot oscillate.When
the loop os broken base current flows through T1 and the circuit starts
oscillating,sounding an alarm.
ADVANTAGES:
Can be controlled by any ordinary TV/VCR/VCD remote.
Can be used to switch device’s which require high voltage and high current.
Can be used to switch any other 9V logic device by using the output across the relay
coil terminal
In the buzzer cuircuit since both the transitors are made from the silicon very little
power is drawn from the battery.
LIMITATIONS:
The operating distance is limited by the transmitting power of the IR source.
Two units (not needed to operated simultaneously) cannot be juxtaposed.
Requires external DC power supply.
Due to the relay the circuit becomes bulky and requires high input power
FUTURE SCOPE:
36
We can further improve the circuit in that instead of using the simple IR, which
is a highly directional, we can further incorporate the technologies like BLUETOOTH or
RFID so that we can operate this from very high distance
REFERENCES:
www.electronicsforu.com
www.datasheetarchive.com
www.kpsec.freeuk.com
37