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Unformatted text preview: CIRCUIT IDEAS CLAP SWITCH
MOHAMMAD USMAN QURESHI I
S.C. ere’s a clap switch free from false
triggering. To turn on/off any ap
pliance, you just have to clap
twice. The cir-cuit changes its output state
only when you clap twice within the set
time period. Here, you’ve to clap within 3
The clap sound sensed by condenser
microphone is amplified by transistor T1.
The amplified signal provides negative pulse depending on the selected values of R7 and
C3. This ‘on’ time (T) of IC1 can be calculated using the following relationship:
where R7 is in ohms and C3 in microfarads.
On first clap, output pin 3 of IC1 goes
high and remains in this standby position
for the preset time. Also, LED1 glows for
this period. The output of IC1 provides
supply voltage to IC2 at its pins 8 and 4. On second clap, a negative pulse triggers IC2 and its output pin 3 goes high for
a time period depending on R9 and C5.
This provides a positive pulse at clock pin
14 of decade counter IC 4017 (IC3). Decade counter IC3 is wired here as a
Each pulse applied at clock pin 14
changes the output state at pin 2 (Q1) of
IC3 because Q2 is connected to reset pin
15. The high output at pin 2 drives transistor T2 and also energises relay RL1. LED2 to pin 2 of IC1 and IC2, triggering both the
ICs. IC1, commonly used as a timer, is
wired here as a monostable multivibrator.
Trigging of IC1 causes pin 3 to go high and
it remains high for a certain time period Now IC2 is ready to receive the triggering
signal. Resistor R10 and capacitor C7 connected to pin 4 of IC2 prevent false triggering when IC1 provides the supply voltage to IC2 at first clap. indicates activation of relay RL1 and on/off
status of the appliance. A free-wheeling
diode (D1) prevents damage of T2 when
This circuit costs around Rs 80. H ELECTRONICS FOR YOU MAY 2003 ...
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- Spring '10