14-03-2012, 02:58 PM
CLAP SWITCH
[attachment=18327]
Here’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
seconds.
The clap sound sensed by condenser
microphone is amplified by transistor T1.
The amplified signal provides negative pulse
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
depending on the selected values of R7 and
C3. This ‘on’ time (T) of IC1 can be calculated
using the following relationship:
T=1.1R7.C3
seconds
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.
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.
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
bistable.
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
