ELECTRONIC CRICKET KIT

MODEL K-16

Assembly and Instruction Manual

Elenco Electronics, Inc.

TM

TM
Copyright © 1989, 2002 Elenco Electronics, Inc. Revised 2003 REV-E 753216
PARTS LIST
If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this electronic cricket kit from a distributor, catalog, etc., please contact ElencoTM Electronics
(address/phone/e-mail is at the back of this manual) for additional assistance, if needed.
RESISTORS
Qty. Symbol Value Color Code Part #
1 R6 360W 5% 1/4W orange-blue-brown-gold 133600
1 R5 1kW 5% 1/4W brown-black-red-gold 141000
1 R3 1.5kW 5% 1/4W brown-green-red-gold 141500
1 R2 22kW 5% 1/4W red-red-orange-gold 152200
1 R4 100kW 5% 1/4W brown-black-yellow-gold 161000
1 R1 1MW 5% 1/4W brown-black-green-gold 171000

CAPACITORS
Qty. Symbol Value Description Part #
1 C2 .01mF (103) Discap 241031
1 C1 100mF Electrolytic 281044

SEMICONDUCTORS
Qty. Symbol Value Description Part #
2 Q1, Q3 2N3904 Transistor NPN 323904
2 Q2, Q4 2N3906 Transistor PNP 323906

MISCELLANEOUS
Qty. Symbol Description Part #
1 PC Board 518016
1 SW1 Switch 541102
1 24” Solder Roll 551124
1 B1 Battery Snap 590098
1 SPK1 Speaker 8W 590102
2 4” Wire 814620

PARTS IDENTIFICATION
Resistor Transistor Switch Capacitor

Electrolytic Discap

Battery Snap Speaker

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

BAND 1 BAND 2 Multiplier Resistance

1st Digit 2nd Digit Tolerance
Color Digit Color Digit Color Multiplier Color Tolerance
Black 0 Black 0 Black 1 Silver +10%
Brown 1 Brown 1 Brown 10 Gold +5%
Red 2 Red 2 Red 100 Brown +1%
Orange 3 Orange 3 Orange 1,000 Red +2%
Yellow 4 Yellow 4 Yellow 10,000 Orange +3%
Green 5 Green 5 Green 100,000 Green +.5%
Blue 6 Blue 6 Blue 1,000,000 Blue +.25%
Violet 7 Violet 7 Silver 0.01 Violet +.1%
Gray 8 Gray 8 Gold 0.1
White 9 White 9
BANDS
1 2 Multiplier Tolerance

IDENTIFYING CAPACITOR VALUES

Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or mF (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.

For the No. 0 1 2 3 4 5 8 9

Multiplier
Multiply By 1 10 100 1k 10k 100k .01 0.1

First Digit Note: The letter “R” may be used at times

10mF 16V

to signify a decimal point; as in 3R3 = 3.3

Second Digit
Multiplier

103K Tolerance
The letter M indicates a tolerance of +20%
100V 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 .01mF 100V

METRIC UNITS AND CONVERSIONS

Abbreviation Means Multiply Unit By Or 1. 1,000 pico units = 1 nano unit
p Pico .000000000001 10-12 2. 1,000 nano units = 1 micro unit
n nano .000000001 10-9
m micro .000001 10-6 3. 1,000 micro units= 1 milli unit
m milli .001 10-3 4. 1,000 milli units = 1 unit
– unit 1 100 5. 1,000 units = 1 kilo unit
k kilo 1,000 103
M mega 1,000,000 106 6. 1,000 kilo units = 1 mega unit
-2-
CIRCUIT OPERATION
Basically, the Electronic Cricket is a very high frequency oscillator which is turned on for a very short period of
time, which makes it very difficult to find.

Figure 1
Figure 1 shows the block diagram of the Electronic Cricket. The circuit consists of two oscillators, a very low
frequency one cycle every two minutes and a very high 10,000 cycles per second. The low frequency oscillator
controls the high frequency oscillator and will allow it to oscillate for about 5 seconds every two minutes. The
circuit will automatically turn off the 10,000 cycles oscillator until it’s ready for the next cycle.

OPERATION OF THE LOW FREQUENCY OSCILLATOR

Figure 2 shows the schematic diagram of the low frequency oscillator. When the power is turned on, a current
(I1) will flow through resistor R1, turning on the base of transistor Q1. This in turn produces a much larger
current (I2) in the collector of Q1 and into the emitter base of Q2, turning transistor Q2 on very strongly. Now,
the collector of Q2 produces a comparatively larger current I3, rapidly charging capacitor C1. C1 sends a
current into the base of Q1 which further increases current I2 and I3. This action is known as positive feedback
and occurs in about 5 seconds. Note that C1 charges through the 22,000 ohm resistor R2. Once this happens,
current in C1 reverses itself turning transistor Q1 and Q2 off. Capacitor C1 reverses itself turning transistor Q1
and Q2 off. Capacitor C1 now must discharge through R2, R3 and R1. These values add up to 1,023,500 ohms
or a very long time compared to the 22,000 ohm charging resistance. The result is a very short on time and
very long off time for transistor Q1 and Q2 as shown in Figure 3.
I2
Figure 2 R1
Q2
I1
+ Q1
I3
9V 5 SEC 2 MIN
R3 OUTPUT
+ ON TIME OFF TIME
R2 C1
R3
Figure 3

OPERATION OF THE HIGH FREQUENCY OSCILLATOR

Refer to the schematic diagram on page 5. Note that transistor Q3 and Q4 form a second oscillator very similar
to oscillator Q1 and Q2. The only difference is the value of capacitor C2 and resistor R5. C2 is much smaller
in capacitance. This causes the oscillator to oscillate at a much higher frequency, 10,000 cycles per second.
Also, note that the input of Q3 is driven from the same point as the input of transistor Q1. (R1 is very high in
value and not important for this consideration). This results in transistor Q3 being on when Q1 is on,
remembering Q1 is on only for about 5 seconds every two minutes. Therefore, oscillators Q3 and Q4 will only
oscillate for 5 seconds every two minutes (refer to Figure 4). The resulting burst of oscillation are fed to the
speaker, which is then heard as our mysterious noise.

5 SEC 2 MIN

If you wish to change the duration of the burst, you can change the value of resistor R2. A larger value will
lengthen the burst. To change the time between bursts, you must change the value of resistor R1. Lowering
the value of R1 will decrease the time between bursts. Resistors R4 and R5 will change the frequency of the
high frequency oscillator.
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CONSTRUCTION
Introduction
The most important factor in assembling your K-16 Electronic Cricket 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.

Safety Procedures
• Wear eye protection when soldering.
• Locate soldering iron in an area where you do not have to go around it or reach over it.
• Do not hold solder in your mouth. Solder contains lead and is a toxic substance. Wash your hands
thoroughly after handling solder.
• Be sure that there is adequate ventilation present.

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 of 63/37 alloy.
DO NOT USE ACID CORE SOLDER!

What Good Soldering Looks Like Types of Poor Soldering Connections

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

1. Solder all components from Soldering Iron 1. Insufficient heat - the

Rosin
the copper foil side only. solder will not flow onto the
Component Lead
Push the soldering iron tip lead as shown.
against both the lead and Foil
the circuit board foil.

Soldering iron positioned

Circuit Board
incorrectly.

2. Insufficient solder - let the

2. Apply a small amount of solder flow over the Solder
Soldering Iron
solder to the iron tip. This connection until it is
allows the heat to leave the Solder
covered. Use just enough
iron and onto the foil. solder to cover the
Immediately apply solder to Foil
connection. Gap
the opposite side of the Component Lead
connection, away from the
iron. Allow the heated 3. Excessive solder - could
component and the circuit make connections that you
foil to melt the solder. Solder
did not intend to between
adjacent foil areas or
3. Allow the solder to flow
Solder Soldering Iron terminals.
around the connection.
Then, remove the solder
and the iron and let the Foil
connection cool. The
solder should have flowed 4. Solder bridges - occur
Soldering Iron
smoothly and not lump when solder runs between
around the wire lead. circuit paths and creates a
short circuit. This is usually
caused by using too much
4. Here is what a good solder solder. To correct this,
connection looks like. simply drag your soldering
iron across the solder Foil Drag
bridge as shown.

-4-
ASSEMBLE COMPONENTS TO THE PC BOARD

Black

Red
SPK - Speaker B1 - Battery Snap - Insert the
black wire into the negative (–)
4” Speaker Wires hole and the red wire into the
Q1 - 2N3904 Transistor positive (+) hole.
(see Figure A) SW1 - Slide Switch
Q2 - 2N3906 Transistor C1 - 100mF Electrolytic Cap.
(see Figure A) (see Figure B)
Q4 - 2N3906 Transistor R2 - 22kW 5% 1/4W Resistor
(see Figure A) (red-red-orange-gold)
Q3 - 2N3904 Transistor R1 - 1MW 5% 1/4W Resistor
(see Figure A)
(brown-black-green-gold)
C2 - .01mF (103) Discap
R6 - 360W 5% 1/4W Resistor
R3 - 1.5kW 5% 1/4W Resistor (orange-blue-brown-gold)
(brown-green-red-gold) R4 - 100kW 5% 1/4W Resistor
R5 - 1kW 5% 1/4W Resistor (brown-black-yellow-gold)
(brown-black-red-gold)

Foil Side of PC Board

Figure A Figure B
Mount the transistor on the position shown. Make Electrolytic capacitors have polarity.
sure that the flat side of the transistor agrees with Mount the capacitor with the positive
the flat side of the marking on the PC board. lead in the hole marked (+) on the PC
Leave 1/4” between the transistor and the PC board.
board.

Polarity
Flat Marking

(–) (+)

-5-
TROUBLESHOOTING
Contact Elenco Electronics if you have any problems. DO NOT contact your place of purchase as they will not
TM

be able to help you.

One of the most frequently occurring problems is poor solder connections.
a) Tug slightly on all parts to make sure that they are indeed soldered.
b) All solder connections should be shiny. Resolder any that are not.
c) Solder should flow into a smooth puddle rather than a round ball. Resolder any connection that has
formed into a ball.
d) Have any solder bridges formed? A solder bridge may occur if you accidentally touch an adjacent foil
by using too much solder or by dragging the soldering iron across adjacent foils. Break the bridge with
your soldering iron.

REMEDY - NO SOUND
1. Battery - Use a fresh 9 volt battery.
2. Switch - Check the switch by placing a clip lead across its terminals. If the cricket now works, then the
problem is with the switch.
3. Transistors - Be sure that the transistors are in their correct positions. Also, look to see that the flat side is
in the correct direction.
4. Capacitor C1 - Be sure that the negative lead is in the correct hole in the PC board.

REMEDY - CIRCUIT WILL NOT TURN OFF

1. Slow Oscillator Circuit - The problem is C1 not discharging. Check resistors R1 and R2 to make sure that
they are in the right place.

SCHEMATIC DIAGRAM

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QUIZ
1. There are ________________ oscillators in the Electronic Cricket.
2. The frequency of these oscillators are ________ cycles per two minutes and ________ cycles per second.
3. The on-time for transistors Q1 and Q2 of the low frequency oscillator is ____________ seconds.
4. The off-time for transistors Q1 and Q2 of the low frequency oscillator is ____________ minutes.
5. The on-time for the high frequency oscillator is ____________ seconds.
6. Capacitor C1 and resistor R2 are part of the positive _____________ for the oscillator.
7. Oscillators Q3 and Q4 are much higher on frequency because resistor R5 and capacitor C2 are _________
in value.
8. The charging path for capacitor C2 is transistor Q4, resistor R5 and transistor ________.
9. If you wish to decrease the time between sound burst, you must decrease resistor ________.
10. The output of transistor Q4 is fed to the __________.

Answers: 1. two; 2. one, 10,000; 3. five; 4. two; 5. five; 6. feedback; 7. smaller; 8. Q3; 9. R1; 10. speaker

TM
Elenco Electronics, Inc.
150 W. Carpenter Avenue
Wheeling, IL 60090
(847) 541-3800
http://www.elenco.com
e-mail: elenco@elenco.com