Elenco 3 1-2 Digit Cap - Trans. Kit User Manual

DIGITAL MULTIMETER KIT

MODEL M-2666K

WIDE RANGE DIGITAL MULTIMETER WITH

CAPACITANCE AND TRANSISTOR TESTING FEATURES

Assembly and Instruction Manual

ELENCO

®

Copyright © 2010 by ELENCO®All rights reserved. Revised 2010 REV-C 753128

No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.

-1-

INTRODUCTION

Range

Switches

Current

Shunts

AC

Converter

Ohms

Converter

Voltage

Divider

Function
Switches

A/D

Converter

and

Display

Driver

Display

Decimal

Point

DC
Analog
Data

V

Ω

VAC

VAC/mA AC

mA

mA

Ω

mA

COMM

V/Ω

V

Figure 1 Simplified Block Diagram

THEORY OF OPERATION

A block diagram of the M-2666K is shown in Figure 1.
Operation centers around a custom LSI chip. This IC
contains a dual slope A/D converter, display, latches,
decoder and the display driver. A block diagram of
the IC functions is shown in Figure 6. The input
voltage, current or ohm signals are conditioned by the
function and selector switches to produce and output
DC voltage between 0 and +199mV. If the input signal

is 100VDC, it is reduced to 100mVDC by selecting a
1000:1 divider. Should the input be 100VAC, then
after the divider it is processed by the AC converter to
produce 100mVDC. If current is to be read, it is
converted to a DC voltage via internal shunt resistors.
For resistance measurements, an internal voltage
source supplies the necessary 0-199mV voltage to be
fed to the IC input.

The input of the 7106 IC is fed to an A/D (analog to
digital) converter. Here the DC voltage amplitude is
changed into a digital format. The resulting signals
are processed in the decoders to light the appropriate
LCD segment.

Timing for the overall operation of the A/D converter
is derived from an external oscillator whose
frequency is selected to be 40kHz. In the IC, this

frequency is divided by four before it clocks the
decade counters. It is further divided to form the three
convert-cycle phases. The final readout is clocked at
about three readings per second.

Digitized measurements data is presented to the
display as four decoded digits (seven segments) plus
polarity. Decimal point position on the display is
determined by the selector switch setting.

Assembly of your M-2666K Digital Multimeter Kit will
prove to be an exciting project and give much
satisfaction and personal achievement. If you have
experience in soldering and wiring technique, you
should have no problems. For the beginner, care
must be given to identifying the proper components
and in good soldering habits. Above all, take your
time and follow the easy step-by-step instructions.
Remember, “An ounce of prevention is worth a
pound of cure”.

The meter kit has been divided into a number of
sections to make the assembly easy and avoid
major problems with the meter operation.

Section A - Meter display circuit assembly.
Section B - DC voltage and current circuit

assembly.

Section C - AC voltage and current circuit

assembly.
Section D - Resistance & buzzer circuit assembly.
Section E - Capacitance and transistor testing

circuit assembly.
Section F - Final assembly.

During autozero, a ground reference is applied as an
input to the A/D converter. Under ideal conditions the
output of the comparator would also go to zero.
However, input-offset-voltage errors accumulate in the
amplifier loop, and appear at the comparator output as
an error voltage. This error is impressed across the AZ
capacitor where it is stored for the remainder of the
measurement cycle. The stored level is used to provide
offset voltage correction during the integrate and read
periods.

The integrate period begins at the end of the autozero
period. As the period begins, the AZ switch opens and
the INTEG switch closes. This applies the unknown
input voltage to the input of the A/D converter. The
voltage is buffered and passed on to the input of the
A/D converter. The voltage is buffered and passed on
to the integrator to determine the charge rate (slope)
on the INTEG capacitor. At the end of the fixed
integrate period, the capacitor is charged to a level
proportional to the unknown input voltage. This voltage
is translated to a digital indication by discharging the

capacitor at a fixed rate during the read period, and
counting the number of clock pulses that occur before
it returns to the original autozero level.

As the read period begins, the INTEG switch opens
and the read switch closes. This applies a known
reference voltage to the input of the A/D converter. The
polarity of this voltage is automatically selected to be
opposite that of unknown input voltage, thus causing
the INTEG capacitor to discharge as fixed rate (slope).
When the charge is equal to the initial starting point
(autozero level), the read period is ended. Since the
discharge slope is fixed during the read period, the
time required is proportional to the unknown input
voltage.
The autozero period and thus a new measurement
cycle begins at the end of the read period. At the same
time, the counter is released for operation by
transferring its contents (previous measurement value)
to a series of latches. This stored stat is then decoded
and buffered before being used for driving the LCD
display.

-2-

AZ

READ

+REF

(FLYING

CAPACITOR)

UNKNOWN

INPUT

VOLTAGE+

INTEG

INTEG

AZ

AZ

READ AZ

INTEG.

TO
DIGITAL
CONTROL
LOGIC

COUNTER OUTPUT

+.20

.15

.10

.05

0

0

10,000

1000500

0

166.7mS

1500

2000

Figure 2 Dual Slope A/D Converter

AZ

COMPARATOR

INTEGRATOR

BUFFER

AMP

EXTERNAL

INPUTS

A/D CONVERTER

A simplified circuit diagram of the analog portion of
the A/D converter is shown in Figure 2. Each of the
switches shown represent analog gates which are
operated by the digital section of the A/D converter.
Basic timing for switch operation is keyed by an
external oscillator. The conversion process is
continuously repeated. A complete cycle is shown in
Figure 2.

Any given measurement cycle performed by the A/D

converter can be divided into three consecutive time
periods: autozero (AZ), integrate (INTEG) and read.
Both autozero and integrate are fixed time periods.
A counter determines the length of both time
periods by providing an overflow at the end of every
1,000 clock pulses. The read period is a variable
time, which is proportional to the unknown input
voltage. The value of the voltage is determined by
counting the number of clock pulses that occur
during the read period.

-3-

VOLTAGE MEASUREMENT

Figure 3 Simplified Voltage Measurement Diagram

Figure 4 Simplified Current Measurement Diagram

200mV

Volts

9MΩ

900kΩ

90kΩ

9kΩ

9Ω

Common

750V

200V

20V

2V

AC to DC
Converter

AC

DC

Low Pass

Filter

100mV

Ref

7106

200μA

A

900Ω

2mA

20mA

200mA

20A

COM

AC - DC

Converter

AC

DC

Low Pass

Filter

100mV

Ref

7106

Figure 3 shows a simplified diagram of the voltage
measurement function.
The input divider resistors add up 10MΩ with each
step being a division of 10. The divider output
should be within –0.199 to +0.199V or the overload

indicator will function. If the AC function is selected,
the divider output is AC coupled to a full wave
rectifier and the DC output is calibrated to equal the
rms level of the AC input.

Figure 4 shows a simplified diagram of the current
measurement positions.
Internal shunt resistors convert the current to
between –0.199 to +0.199V which is then

processed in the 7106 IC to light the appropriate
LCD segments. If the current is AC in nature, the AC
converter changes it to the equivalent DC value.

CURRENT MEASUREMENT

90Ω

9Ω

0.99Ω

0.01Ω

20A

-4-

RESISTANCE MEASUREMENTS

Figure 5 shows a simplified diagram of the resistance measurement function.

Figure 5 Simplified Resistance Measurement Diagram

External
Resistor

100Ω

Voltage
Source

100mV

Ref

Low Pass

Filter

7106

A simple series circuit is formed by the voltage
source, a reference resistor from the voltage divider
(selected by range switches), and the external
unknown resistor. The ratio of the two resistors is
equal to the ratio of their respective voltage drops.
Therefore, since the value of one resistor is known,
the value of the second can be determined by using
the voltage drop across the known resistor as a
reference. This determination is made directly by the
A/D converter.

Overall operation of the A/D converter during a
resistance measurement is basically as described
earlier in this section, with one exception. The
reference voltage present during a voltage
measurement is replaced by the voltage drop
across the reference resistor. This allows the voltage
across the unknown resistor to be read during the
read period. As before, the length of the read period
is a direct indication of the value of the unknown.

hFE MEASUREMENT

Figure 6 shows a simplified diagram of the hFE
measurement function. Internal circuits in the 7106
IC maintain the COMMON line at 2.8 volts below
V+. When a PNP transistor is plugged into the
transistor socket, base to emitter current flows
through resistor R49. The voltage drop in resistor
R49 due to the collector current is fed to the 7106
and indicates the h

FE of the transistor. For an NPN

transistor, the emitter current through R50 indicates
the h

FE of the transistor.

Figure 6

The capacitor circuit consists of four op­amps. IC3 D&A form an oscillator, which is
applied to the test-capacitor through the test
leads. The capacitor couples the oscillator to
pin 6 of IC3B. The amount of voltage
developed at pin 6 is indicative of the
capacitors ESR value. IC3B and C amplify
the signal which is seen at pin 8. The AC
signal is then converted to a DC voltage and
displayed on the meter.

900Ω

9kΩ

90kΩ

900kΩ

9MΩ

20MΩ

2MΩ

200kΩ

20kΩ

2kΩ

200Ω

100mV

Ref

Low Pass

Filter

7106

R50

220kΩ

COM

220kΩ

10Ω

PNP NPN

E

C

B

B

C

E

V+

CAPACITANCE MEASUREMENT

Figure 7

-5-

Figure 8 7106 Functions

a

b

a

b

c

d

e

f

g

TYPICAL SEGMENT OUTPUT

0.5mA

2mA

V+

Segment

Output

Internal Digital Ground

LCD PHASE DRIVER

LATCH

7 Segment

Decode

7 Segment

Decode

7 Segment

Decode

Thousand

Hundreds

Tens Units

*

CLOCK

To Switch Drivers

From Comparator Output

-4

LOGIC CONTROL

Internal Digital Ground

200

BACKPLANE

28

V+

TEST

V

500Ω

3

34

6.2V

1V

* Three inverters.

One inverter shown for clarity.

7

6

4

OSC 1

OSC 2

OSC 3

DIGITAL SECTION

ANALOG SECTION of 7106

C

REF

R

INT

C

AZ

C

INT

INT

C

REF

+

REF HI

REF LO

C

REF

BUFFER

V+

35

42 44 43

41

36

37

8

AUTO
ZERO

+

A-Z &

Z1

A-Z &
Z1

A-Z

DE (+)

DE (+)

DE (-)

DE (-)

IN HI

COMMON

IN LO

40

39

INT

10μA

V+

38

INT

+

+

+

2.8V

A-Z & DE(+

)

& Z1

34

V

Z1

6.2V

A-Z

COMPARATOR

ZERO
CROSSING
DETECTOR

POLARITY
FLIP/FLOP

TO
DIGITAL
SECTION

INTEGRATOR

a

b

c

d

e

f

g

a

b

c

d

e

f

g

-6-

ASSEMBLY

The meter kit has been divided into a number of
sections to make the assembly easy and avoid
major problems with the meter operation.

ONLY OPEN COMPONENT BAGS THAT ARE
CALLED FOR IN YOUR ASSEMBLY PROCEDURE.
DO NOT OPEN ANY OTHER BAGS.

Do not build more than one section of your meter at
a time. Your instructor must approve the proper
operation of the section you have built before you
proceed to the next section. This procedure will
minimize the problems you may have at the
completion of the project.

Your kit program is divided into Sections “A – F”. The
small parts bags will be marked accordingly. The
sections are listed below.

Section A - Meter Display Circuit Assembly.

Section B - DC Voltage and Current Circuit

Assembly.

Section C - AC Voltage and Current Circuit

Assembly.

Section D - Resistance & Buzzer Circuit Assembly.

Section E - Capacitance and Transistor Circuit

Assembly.

Section F - Final Assembly.

IMPORTANT CONSTRUCTION NOTES

1. Wash your hands with soap and water before you
assemble this kit. The high impedance areas on
the circuit board can be contaminated by salt and
oil from your skin. If these areas become
contaminated, your completed multimeter may
not meet the listed specifications. Handle the
circuit board only by its edges.

2. Avoid any excessive accumulation of resin build­up whenever you solder a connection.

3. Take your time assembling the circuit board.
Work at a slow pace. Remember that accuracy is
far more important than speed.

4. When you perform the steps in assembly, identify
each respective component before you install it.
Then position it over its outline on the top legend
side of the PC board, unless otherwise indicated.

5. Check for the proper polarity of ICs, diodes,
electrolytic capacitors, battery snap and LCD.

BATTERIES

• Do not short circuit the battery terminals.

• Never throw battery in a fire or attempt to open its
outer casing.

• Use only 9V type, alkaline or carbon zinc battery
(not included).

• Insert battery with correct polarity.

• Non-rechargeable batteries should not be
recharged. Rechargeable batteries should only be
charged under adult supervision, and should not
be recharged while in the product.

• Remove battery when it is used up.

• Batteries are harmful if swallowed, so keep away
from small children.

-7-

CONSTRUCTION

Solder

Soldering Iron

Foil

Solder

Soldering Iron

Foil

Component Lead

Soldering Iron

Circuit Board

Foil

Rosin

Soldering iron positioned
incorrectly.

Solder

Gap

Component Lead

Solder

Soldering Iron

Drag

Foil

1. Solder all components from the
copper foil side only. Push the
soldering iron tip against both the
lead and the circuit board foil.

2. Apply a small amount of solder to
the iron tip. This allows the heat to
leave the iron and onto the foil.
Immediately apply solder to the
opposite side of the connection,
away from the iron. Allow the
heated component and the circuit
foil to melt the solder.

1. Insufficient heat - the solder will
not flow onto the lead as shown.

3. Allow the solder to flow around
the connection. Then, remove
the solder and the iron and let the
connection cool. The solder
should have flowed smoothly and
not lump around the wire lead.

4.

Here is what a good solder
connection looks like.

2. Insufficient solder - let the
solder flow over the connection
until it is covered.
Use just enough solder to cover
the connection.

3. Excessive solder - could make
connections that you did not
intend to between adjacent foil
areas or terminals.

4. Solder bridges - occur when
solder runs between circuit paths
and creates a short circuit. This is
usually caused by using too much
solder.
To correct this, simply drag your
soldering iron across the solder
bridge as shown.

What Good Soldering Looks Like

A good solder connection should be bright, shiny, smooth, and uniformly
flowed over all surfaces.

Types of Poor Soldering Connections

Introduction

The most important factor in assembling your M-2666K Digital
Multimeter Kit is good soldering techniques. Using the proper soldering
iron is of prime importance. A small pencil type soldering iron of 25 - 40
watts is recommended. The tip of the iron must be kept clean at all

times and well tinned.

Solder

For many years leaded solder was the most common type of solder
used by the electronics industry, but it is now being replaced by lead­free solder for health reasons. This kit contains lead-free solder, which
contains 99.3% tin, 0.7% copper, and has a rosin-flux core.

Lead-free solder is different from lead solder: It has a higher melting
point than lead solder, so you need higher temperature for the solder to
flow properly. Recommended tip temperature is approximately 700

O

F;
higher temperatures improve solder flow but accelerate tip decay. An
increase in soldering time may be required to achieve good results.
Soldering iron tips wear out faster since lead-free solders are more
corrosive and the higher soldering temperatures accelerate corrosion,
so proper tip care is important. The solder joint finish will look slightly
duller with lead-free solders.

Use these procedures to increase the life of your soldering iron tip when
using lead-free solder:

• Keep the iron tinned at all times.

• Use the correct tip size for best heat transfer. The conical tip is the
most commonly used.

• Turn off iron when not in use or reduce temperature setting when
using a soldering station.

•

Tips should be cleaned frequently to remove oxidation before it becomes
impossible to remove. Use Dry Tip Cleaner (Elenco

®

#SH-1025) or Tip

Cleaner (Elenco

®

#TTC1). If you use a sponge to clean your tip, then use

distilled water (tap water has impurities that accelerate corrosion).

Safety Procedures

• Always wear safety glasses or safety goggles to
protect your eyes when working with tools or
soldering iron, and during all phases of testing.

• Be sure there is adequate ventilation when soldering.

•

Locate soldering iron in an area where you do not have to go around
it or reach over it. Keep it in a safe area away from the reach of
children.

• Do not hold solder in your mouth. Solder is a toxic substance.
Wash hands thoroughly after handling solder.

Assemble Components

In all of the following assembly steps, the components must be installed
on the top side of the PC board unless otherwise indicated. The top
legend shows where each component goes. The leads pass through the
corresponding holes in the board and are soldered on the foil side.

Use only rosin core solder.

DO NOT USE ACID CORE SOLDER!

'

PART IDENTIFICATION CARDS

To help identify the resistors and diodes used in the construction of your digital
multimeter we have mounted the diodes and resistors of each section onto a card.
The card will help you find the diodes and resistors quickly. THE PARTS WILL NOT
NECESSARILY BE LISTED IN THE ORDER SHOWN IN THE PARTS LIST
SECTION OR IN THE ASSEMBLY PROCEDURE.

When you are ready to assemble the meter kit, follow the procedure shown. For
an example refer to page 11 for assembly of Section “A”. The first resistor called
for is R8, 470kΩ resistor (yellow-violet-yellow-gold). Locate it on the card ( ), verify
that it is the correct value. Some resistors may be mounted backwards on the card
so you must be certain that you are reading the resistors correctly. When the
correct value has been established, only then will you mount it into its correct
position on the PC board.

IDENTIFYING RESISTOR VALUES

Use the following information as a guide in properly identifying the value of resistors.

M-2666K

SECTION A

5 Bands

1 2

Multiplier

Tolerance

3

4 Bands

1

2

Multiplier

Tolerance

-8-

EXAMPLE

IDENTIFYING CAPACITOR VALUES

Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or μF (microfarads).
Most capacitors will have their actual value printed on them. Some capacitors may have their value printed in
the following manner. The maximum operating voltage may also be printed on the capacitor.

Second Digit

First Digit

Multiplier

Tolerance*

For the No.01234589
Multiply By 1 10 100 1k 10k 100k .01 0.1

Multiplier

Note: The letter “R” may be used at times to
signify a decimal point; as in 3R3 = 3.3

10μF 16V

103K

100V

The letter M indicates a tolerance of +20%
The letter K indicates a tolerance of +10%
The letter J indicates a tolerance of +5%

Maximum Working Voltage

The value is 10 x 1,000 =
10,000pF or .01μF 100V

*

Electrolytic capacitors have a positive
and a negative electrode. The
negative lead is indicated on the
packaging by a stripe with minus
signs and possibly arrowheads.

Warning:

If the capacitor
is connected
with incorrect
polarity, it may
heat up and
either leak, or
cause the
capacitor to
explode.

Polarity
Marking

-9-

RESISTOR READING EXERCISE

(1) yellow-black-black-black-brown

(3) brown-red-violet-red-brown

(5) brown-black-black-black-brown

(7) white-black-black-yellow-green

(9) brown-black-black-orange-green

(11) gray-white-black-black-brown

(2) white-black-black-red-green

(4) green-black-green-brown-green

(6) brown-green-gray-orange-brown

(8) white-black-black-silver-green

(10) orange-white-red-red-brown

(12) brown-brown-black-red-brown

Answers to Resistor Reading Exercise: 1) 400Ω+1%; 2) 90kΩ+.5%; 3) 12.7kΩ+1%; 4) 5.05kΩ+.5%; 5) 100Ω+1%;

6) 158kΩ+

1%; 7) 9MΩ+.5%; 8) 9Ω+.5%; 9) 100kΩ+.5%; 10) 39.2kΩ+1%; 11) 890Ω+1%; 12) 11kΩ+1%;

Before starting assembly of your digital multimeter
project, you should be thoroughly familiar with the 5
band color code system. Many of the resistor values
will be identified by color bands and it is easy to
mistake their value if you read the colors incorrectly

or read the value from the wrong end. Do the
following exercise in resistor values. Place your
answer in the box beneath the resistor. Answers are
on the bottom of this page.

-10-

PARTS LIST - SECTION A

If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this kit from a distributor, catalog, etc., please contact ELENCO®(address/phone/e-mail is at
the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase as they
will not be able to help you.

RESISTORS

Qty. Symbol Description Color Code Part #

r 2 R4, R5 100kΩ 5% 1/4W brown-black-yellow-gold 161000
r 1 R3 200kΩ 5% 1/4W red-black-yellow-gold 162000
r 1 R1 220kΩ 5% 1/4W red-red-yellow-gold 162200
r 3 R7, R8, R9 470kΩ 5% 1/4W yellow-violet-yellow-gold 164700
r 2 R2, R6 1MΩ 5% 1/4W brown-black-green-gold 171000

CAPACITORS

Qty. Symbol Value Description Part #

r 1 C5 100pF (101) Disc 221017
r 1C1 .1μF (104) Mylar (large brown) 251017L
r 3 C2, C3, C4 .1μF (104) Mylar (small yellow) 251017S
r 1C6 22μF Electrolytic (Lytic) 272244S

SEMICONDUCTORS

Qty. Symbol Value Description Part #

r 1 T1 9013 Transistor 2SC9013 329013

MISCELLANEOUS

SECTION A

Meter Display Circuit

Resistor

PARTS IDENTIFICATION

Diode PC Board

Liquid Crystal Display (LCD)

Qty. Description Part #

r 1 LCD 351166
r 1 Zebra 500007
r 1 PC Board M2666K 512666
r 1 Switch On/Off (SW1) 540004
r 1 Battery 9V 590009

Qty. Description Part #

r 1 Battery Snap (Batt) 590098
r 1 LCD Housing 629015
r 1 LCD Cover 629016
r 1 Label Top 723051
r 2 Solder 9LF99

Transistor

Label Top

Display
Housing

Display
Cover

Zebra

LCD

Capacitors

Disc

Lytic

Mylar

C1