A Tool for Finding and Handling Small Parts

62 Issue 221 December 2008 www.circuitcellar.com

mine what other devices might be inparallel with and affecting the deviceunder test (DUT).

WHAT DOES IT DO?The Smart Tweezers meter auto-

matically determines the type of com-ponent, resistor, capacitor, or inductor(RCL), and selects the proper rangeand signal frequency for the highestaccuracy measurement. Using a small32 × 96 dot graphics display, the SmartTweezers meter clearly displays thecomponent type, measurementresults, and test conditions used todetermine the results. The display isdivided into three areas. The central

be seen again! Frankly, I’m surprised I haven’t seen

a good tool like the Advance DevicesSmart Tweezers handheld LCR metersooner (see Photo 1b). The small,lightweight format fits comfortably,enabling operation with just one hand.Although it is designed to easily grabSMT devices with its tweezer-typeprobes, it can perform its magic onthrough-hole parts as well.

You can use the Smart Tweezers(ST) to identify and evaluate loosecomponents and those already sol-dered on a PCB (unpowered). Ofcourse, you may need to have someknowledge of the circuitry to deter-

CIRCUIT CELLAR®

If your work area is like mine, youprobably have a small box that col-lects all the odd components that endup on your bench after a project (seePhoto 1a). I am a little more carefulwhen it comes to surface-mount parts.They are usually purchased as tapedstrips (reels) of parts and are betterprotected from getting jumbled togeth-er with other parts (if left taped). How-ever, one of the big problems withSMT stuff is that it is usually toosmall to be labeled. Thus, you can eas-ily lose track of parts and their values.I can’t tell you how many times I’vepicked up an SMT part only to have itshoot out from the tweezers never to

FROM THE BENCH by Jeff Bachiochi

It’s time to take control of your components.You can identify tiny surface-mount parts with ahandheld LCR meter. The lightweight tool automatically determines the type of component,inductor, capacitor, or resistor (LCR), and selects the proper range and signal frequency forthe most accurate measurement. The component type, measurement results, and testconditions used to determine the results are displayed on a dot-matrix display.

Photo 1a—Here’s a few of the hundreds of unmarked (or unreadable) parts in my “junk” box. Every one of these parts isidentifiable using the Advance Devices Smart Tweezers LCR handheld meter. b—The Smart Tweezers meter can identifya component type and value by picking it up. The auto function will identify capacitors, resistors, and inductors.

Component Control

a) b)

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(and largest) area contains the compo-nent type and determined value. Thetop area shows additional parametersand testing conditions. The bottomarea displays a horizontal bar graphindicating the value’s percentage ofthe test range.

If you’ve had the pleasure of assem-bling any circuit using surface mounttechnology (SMT) components, youprobably have at least one pair oftweezers for picking up and placingsurface-mount devices (SMDs). TheSmart Tweezers meter has conductivepincer-like contacts that can measureand identify an SMD if picked up thecorrect way (see Photo 1b). The smalland lightweight enclosure fits well inyour hand, kind of like writing with apen or pencil. At first, I thought thesmall LCD might be custom glasswith specific glyphs. But after playingwith it a while, I realized it was a sim-ple dot-matrix display. The design canbe used with either of your hands.When configured for lefties, all of the

LCD text and graphics are rotated180°. I’m guessing this is done rathersimply by manipulating the LCD dataand where the data is stored (mirror-ing each most significant for least sig-nificant bit/register).

Automatic mode determines thedevice type (LCR) and measures, cal-culates, and displays the appropriatevalue. Manual modes are available to

force the tests to use particularparameters. All modes are accessedvia a jog dial—actually three switches(push left, push right, and pushdown).

WHAT IS GOING ON?Figure 1 shows the system’s major

building blocks. The microcontrollerof choice is a 16-bit Texas Instruments

www.circuitcellar.com CIRCUIT CELLAR® Issue 221 December 2008 63

Figure 1—A Texas Instruments MSP430F135 microcontroller orchestrates the user I/O, D/A, A/D, and power management circuitry to identify common devices, including resistors,capacitors, inductors, and diodes.

Sourceresistor

VoltageVmp(VA)

Currentamp(IA)

ESDProtection

circuitand DC

dividerswitch Programmable

gain amp

(PGA)

Buffer amp

Power managementcircuit

Reference voltagesource

DUT

MUX

MUX

ADC

DDS

Microcontroller

LCD and Navigation switch

Low-pass filter

Battery

LPF

DC Voltage

Photo 2—The internal PCB has the MSP430F135 microcontroller and all the other SMT parts (except the LCD)mounted on one side. The three button cell batteries can provide over 80 h of use.

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64 Issue 221 December 2008 CIRCUIT CELLAR® www.circuitcellar.com

MSP430F135 (see Photo 2).Besides handling the userinput/output through a jog-dial/LCD, the microcontrollercalculates the impedance of aDUT by measuring the voltageacross it and the currentthrough it, as shown in thefront-end circuitry (see Figure2). The MSP430F135 controlsboth the amplitude and fre-quency of the voltage source(VS) and is typically approxi-mately 1 V (sine wave). VS isapplied to the DUT throughthe source resistance RS. DUTV

is the voltage measured by thefirst amplifier (AU) directlyacross the DUT and is measured byone A/D channel. Current through theDUT (DUTI) is converted to a propor-tional voltage by a second amplifier(AI) and the feedback resistor RI (V =DUTI × RI) so it can be read by a sec-ond A/D channel.

The DUT’s impedance is a combina-tion of resistance and capacitive orinductive reactance. The proportions

of each of these are based on the rela-tionships between applied voltage andthe measured voltage and current.With an ideal resistive DUT, theimpedance, and thus resistance, is thesame because the DUTI and DUTV arein phase. With an ideal capacitorDUT, the impedance is the capacitivereactance because the DUTI will leadthe DUTV by 90°. The capacitance

must be calculated based on:

[1]

With an ideal inductor DUT,the impedance is the inductivereactance because the DUTI

will lag the DUTV by 90°. Theinductance must be calculatedbased on:

[2]

Manufacturing and materi-als will play a role in adevice’s quality. Capacitors,inductors, and even resistorsmay be less than ideal compo-

nents. We all consider a resistor to bepretty much an ideal device. Howev-er, many resistors are made bydepositing a material on a form andetching or cutting a spiral pattern inthe coating, creating a lengthy strip toachieve the required value, but alsolooking a bit like an inductor. This isperhaps more clearly seen in wire-wound resistors. While this is usually

L f XL

= −12 π

C f XC

= −12 π

Figure 2—The analog front end uses a DAC to provide AC excitation to theDUT. The resultant voltage across and current through the device is meas-ured by A/D circuitry to provide data back to the microcontroller.

Voltage signalto ADC

Current signalto ADC

DUT AU

VS

AI

RI

RS

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minimal, it must be considered in cir-cuits where the frequencies used maycause this inductance to affect circuitoperation.

All current-carrying conductors areinductors to some extent. That is, themagnetic field created by a change incurrent in them is not instantaneousand therefore opposes the change.This opposition can be enhanced byproviding a medium (core) that col-lects and hangs onto the magneticenergy, as well as concentrating(wrapping) the conductors around thecore. As shown in the previous equa-tions, there is a direct relationshipbetween the inductance (opposition tochange) and frequency (rate ofchange). Therefore, testing a compo-nent at a number of frequencies isrequired to obtain measurementresults that are within analytical lim-its. It’s likely an inductor will besomewhat less than ideal. Seriesresistance will be part of the DUT’simpedance. This can be determinedby the phase relationship between theDUTV and the DUTI. With the ideal

resistor (phase shift = 0°) and the idealinductor (phase shift = 90°), anyinductor that is not ideal will have aresistive/inductive reactance relation-ship of phase difference equals arctan(XL/R). The relationship (XL/R) is alsoknown as the quality factor (Q). Thecloser the inductor is to ideal, thehigher the Q.

A capacitor, on the other hand,opposes a change in voltage due to itsphysical makeup. The leads of acapacitor are connected to large platesheld just a fraction of an inch apart bythin insulating material. Ideally, thereis infinite resistance between theplates. When a voltage is appliedacross the plates, maximum currentflows because the potential differencebetween the source and the plates isgreatest. Electrons are in fact not flow-ing through the device but beingstored on (or released from) the plates.The electrons create an electric charge(voltage) across the plates. As thepotential between the source voltageand the plate voltage decreases, sodoes the current flow. Capacitance

goes up as the plate size increases orthe spacing decreases. Although thedielectric insulating material alsoaffects capacitance, it has a greatereffect on losses that are affected bythings like temperature and frequen-cy. As shown in the previous equa-tions, there is a direct relationshipbetween the capacitance (oppositionto change) and frequency (rate ofchange). Therefore, testing a compo-nent at a number of frequencies isrequired to obtain measurementresults that are within analytical lim-its. It’s likely a capacitor will besomewhat less than ideal. There willbe some parallel resistance that willbe part of the DUT’s impedance. Thiscan be determined by the phase rela-tionship between the DUTV and theDUTI. With the ideal resistor (phaseshift = 0°) and the ideal capacitor(phase shift = 90°), any nonideal capac-itor will have a resistive/capacitivereactance relationship of phase differ-ence equals arctan (XC/R). The rela-tionship (R/XC) is also known as thedissipation factor (D). The closer the

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enables/disables a beep whenever ameasurement is taken. The DISPLAYsetting lets you set the display’s con-trast and determine whether the dis-play is formatted for right- or left-handuse. Finally, the TIMEOUT settinglets you set the timeout (the delayafter any measurement or selectionbefore shutting off) from 10 to 200 s.

While the Smart Tweezers can meas-ure most devices using the AUTOmode (RES/IND/CAP), you can use themeasurement settings to change orforce a mode of operation. For instance,if you have a wire-wound resistor, youcan select inductor (IND) to determinethe resistor’s inductive reactance due toits physical makeup. If the DUT is adiode, you must force a switch toDIODE mode. A pictograph of a diodewill be displayed with its orientationmatching the polarity of the connec-tion. The VOLTAGE selection allowsfor measurements of up to ±8 V. A tinyslide switch on the side of the casemust be moved to enable this function.(The LCD prompts you when to slideit.) Note that the auto-off function is

66 Issue 221 December 2008 CIRCUIT CELLAR® www.circuitcellar.com

capacitor is to ideal, the lower D will be.

FINGERTIP CONTROLThe jog dial provides up, down, and

select functions. An initial press (inany direction) initializes the SmartTweezers and configures it to the lastselected functions before it turns itselfoff. You can immediately begin takingmeasurements of components. A sec-ond push brings up a menu of func-tions you may choose from. The menuroad map is shown in Figure 3. Choos-ing AUTOSET resets all parameters tothe default setting and returns you toOperational mode. There are twoother selections you can chooseinstead of EXIT, SYSTEM, and MEA-SURE. If you choose SYSTEM, youcan select one of the four system set-tings: SOUND, DISPLAY, TIMEOUT,and SERVICE. If you choose MEA-SURE, you can select one of the sevenmodes of operation: AUTO, RES, IND,CAP, DIODE, VOLTAGE, and TRACE.

The system settings enable you tocustomize the operation of the SmartTweezers. The SOUND setting

disabled while this switch is used.TRACE mode is similar to VOLTAGE.Instead of a text display of the voltagevalue, a graphic display over time isused, like an oscilloscope. You candynamically change the time base usingthe left/right jog dial switches. Becauseof the delicate and sensitive front end,you should not measure live circuitswith more than 1.6 V without selectingVOLTAGE or TRACE modes and mov-ing the slide switch as prompted.

PRACTICAL LIMITSThere are a few things that might seem

obvious but must be taken into consider-ation for the most accurate measure-ments. When measuring small resist-ances, the physical connection resist-ance between the (gold plated) tips andthe DUT is approximately 25 mΩ (thiscan vary with contact pressure). Youmust subtract this from the measuredvalue, if appropriate, when it is a largepercentage of the DUT. For the mostaccurate measurements of small capaci-tors (pF), you should force the test fre-quency into its highest range (10 kHz).

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Measuring physically small size capaci-tors will inherently add a small offset ofup to a couple of puffs (picofarads) dueto the close proximity of the tips. Mea-suring inductive extremes is most accu-rate by forcing the test frequency aswell (highest frequency for low valuesand lowest frequency for high values).

USE ITAfter each project, I spend a little

(sometimes too little) time cleaningup my workspace. It’s not unusual forthere to be a bunch of leftover compo-nents on my bench top. If I’m bad, Isweep them into a box of miscella-neous parts. If I’m worse, I toss themout! Many parts are unique enough tobe easily separated and put back intotheir proper places. Components likeconnectors and ICs (generally any-thing that is large enough) can behandled through divide-and-conquer

techniques. When it comes to smallerdiscrete or SMT parts, I need to getout the hand magnifier to read values.While the colored stripes on 5% resis-tors are noticeable, I often can’t tellwhich end is which with the resistorsthat are 5%. Even though I know 0603SMT resistors have digit values onthem, I can’t make them out, evenwith a magnifier. Other small surface-mount capacitors and inductors haveroom only for a logo. I no longer needto strain my eyes and guess at whichparts I’m trying to store away becauseI can use Smart Tweezers to pick up,identify, and place the part in one easymovement.

I’ve always used a small pair oftweezers to help position SMT compo-nents on PCBs that I hand assemble.I’m pretty good at soldering tinydevices. One of the most frustratingthings is to find that I’ve either used

the wrong part in the right place orthe right part in the wrong place.Being able to verify a part’s type andvalue prior to hand soldering is helpfulin the long run. Likewise, being able toidentify components and values thathave been placed and soldered can savetime. You don’t have to remove andreplace a part because you don’t knowif it’s the right part. This goes a longway in reducing stress, especiallywhen a circuit is not working correct-ly. Of course, you need to know howthe component is connected in the cir-cuit to determine if its measured valueis being affected by the surroundingcomponents. Note that you shouldalways measure components with thecircuit in an unpowered state, unlessyou are specifically using the SmartTweezers in the voltage mode.

Have you ever had a circuit youwere trying to understand? Maybe you

Figure 3—The dot-matrix LCD provides resultant data as well as function menus for changing default parameters. You can scroll through the menu selections using the jogdial’s left/right switches. By pressing it, you can choose the highlighted selection. Use this chart to follow the menu hierarchy.

Autoset

System

Measure

Display

Sound

Setting

Mode

Mode

Mode

Mode

Mode

Mode

Mode

Offset

Battery

S/N

Sound on

Sound off (except MENU mode)

Rotate JogDial Left/Right to select menu itemsPush JogDial to set selected parameters or exit

Right-hand display indication mode

Left-hand display indication mode

Display contrast adjustment

Power off timeout 10 to 200 s

DC Offset adjustment

Battery voltage indicator

Serial number indicator

Exit

Exit

Tone

Hold

R/D/Q

Period

T FREQ

Default

Off

On

Off

On

D/Q

R

1 s

0.5 s

2 s

10 kHz

1 kHz

120 Hz

100 Hz

Auto

resistance (less than 40 Ω)measurements

Sound mode for small

Reading mode settings

type selectionSecondary parameter

Readings period settings

Fixed test frequency modefor specific measurement

Autoselection of the test frequency

Set all parameters to default

Auto

10> <2005Timeout

Service

Exit

Exit

Exit

Exit

Res

Ind

Cap

Diode

Voltage

Trace

Auto-measurement mode

Resistance measurement mode

Inductance measurement mode

Capacitance measurement mode

Diode measurement mode

DC Voltage mode (up to ±8 V)

Dynamic signals (AC Voltage)

Pus

h Jo

gDia

l to

ente

r m

enu

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68 Issue 221 December 2008 CIRCUIT CELLAR® www.circuitcellar.com

Jeff Bachiochi (pronounced BAH-key-AH-key) has been writing forCircuit Cellar since 1988. His back-ground includes product design andmanufacturing. You can reach him atjeff.bachiochi@imaginethatnow.comor at www.imaginethatnow.com.

SOURCESSmart Tweezers Handheld LCR meterAdvance Devices Corp.www.advancedevices.com

MSP430F135 Microcontroller Texas Instruments, Inc. www.ti.com

needed to determine the cut-off fre-quency of an analog filter? The ST is agreat tool to help you identify thecomponents and values used in a cir-cuit so you can make the calculationnecessary to determine operatingparameters. While the Smart Tweezersis made for measuring those parts thatfit between its fingertips, you can putclip leads on its tips and measurephysically larger parts as well.

Are you a coil winder? Say you needthat power inductor for some switch-ing circuit and want to wrap your owncoil. After winding what you’ve calcu-lated to be the proper turn ratio, youwill wonder if it will be close enoughto do the job. The Smart Tweezers cangive you peace of mind by measuringthe inductance (and the ESR as well).You can also experiment with how theinductance is affected by the corematerial you are using.

PORTABILITYThanks to the extremely low power

requirements of Texas Instruments’sMSP430F135, the Smart Tweezers

device operates for over 80 h on threealkaline (357 A) button cells. For me,shelf life will most likely be the limit-ing factor on operational life. Theauto-off feature will keep your batter-ies from running down should you for-get to turn it off. Even with intermit-tent use in a production environment,your batteries should last weeks. Ifyou don’t want to be bothered withkeeping a supply of batteries on hand,there is a rechargeable option.

You can upgrade your standardSmart Tweezers device any timebecause the inductive charger is field-upgradeable. Simply replace threealkaline cells in the Smart Tweezerswith the 3.6-V NiMH battery and sol-der in the inductive receiver. Theinductive transmitter is fully assem-bled and can run off either an AC wallwart or via USB (power only).

Inductive charging is becoming a hotitem for cell phones and other devices.I think inductive charging deserves acolumn of its own, so let me know ifyou’d like to see more on that technol-ogy, or any other topic for that mater.

The Smart Tweezers device is justthe kind of tool I would have liked todesign. It combines a good mix of ana-log and digital circuitry into a com-pact, easy-to-use unit. The low-powerdesign is kind on current consump-tion, which helps stretch battery life.You will find this tool invaluablewhen verifying, analyzing, and identi-fying components both in and out ofcircuit. I

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