Elenco Sound Activated Switch - Manual (Page 3)

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INTRODUCTION
Just clap your hands together twice and watch the Sound Activated Switch turn on the light emitting diode
(LED). Clap twice more and watch the LED turn off.
THEORY OF OPERATION
Figure 1 shows the block diagram of the Sound Activated Switch. It consists of a transistor amplifier, a transistor
switch and two types of digital circuits, a one-shot and a flip-flop.
TRANSISTOR
AMPLIFIER
TRANSISTOR
SWITCH
ONE-SHOT FLIP-FLOP
Figure 1
IDENTIFYING RESISTOR VALUES
Use the following information as a guide in properly identifying the value of resistors.
A waveform is created when hands are clapped
together. The MIC senses this waveform and
couples it to the base of Q1 by capacitor C1 (refer
to schematic diagram). The transistor is configured
as a common emitter amplifier since the AC signal is bypassed to ground by capacitor C2. The
transistor amplifier is set for a gain of 50, so the
waveform is amplified 50 times. Capacitor C3
couples the amplified waveform to the input of the
first digital circuit.
THE TRANSISTOR AMPLIFIER
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.
Multiplier
For the No. 0 1 2 3 4 5 8 9
Multiply By 1 10 100 1k 10k 100k .01 0.1
Second digit
First digit
Multiplier
Tolerance*
Note: The letter “R” may be used at times to signify a
decimal point; as in 3R3 = 3.3
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
(may or may not appear on the cap)
The value is 10 x 10 = 100pF, +10%, 50V
*
CERAMIC DISC MYLAR
First digit
Second digit
Multiplier
Tolerance*
2A222J
100V
The value is 22 x 100 =
2,200pF or .0022
μF, +5%, 100V
101K
50V
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. Also,
the negative lead of a radial electrolytic is
shorter than the positive one.
Warning:
If the capacitor is connected
with incorrect polarity, it may
heat up and either leak, or
cause the capacitor to
explode.
Polarity
marking
(+)
(–)