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| Sound Operated Timer With IC 555 |
This sound operated
timer is based on LM324 quad-operational amplifier and NE555 timer. Time delay
can be set from a few seconds to 30 minutes. It can also be used as a sound
sensitive burglar alarm.
Sound operated timer
circuit and working
Circuit diagram of the
sound operated timer is shown in Fig. 1. Output pin 1 of LM324 (IC1) is fed to
pin 2 of NE555 (IC2) through capacitor C3. IC2 is configured as a monostable
multivibrator. Sound signal, like clapping, sensed by condenser microphone MIC1
is amplified by IC1.
Sound Operated Timer With IC 555
Amplified signal is fed to
trigger pin 2 of IC2. Output pin 3 of IC2 goes high and relay RL1 gets
energised for a time delay set by potmeter VR2. Time delay can be set from a
few seconds to 30 minutes. Energisation of the relay is indicated by the
glowing of LED1.
Relay RL1 is de-energised after the time delay. NE555 can source
200mA current; so, an ordinary relay can be directly connected to IC2’s output
without an extra transistor driver. Use a good-quality microphone for maximum
sensitivity.
Construction
and testing
An actual size, single side PCB layout for the sound operated
timer is shown in Fig. 2 and its component layout in Fig. 3. After assembling
the circuit on the PCB, enclose it in a suitable plastic box.
The circuit needs a
6V-12V DC power supply. When MIC1 captures the sound made by an intruder, RL1
gets energised. An electric lamp may be connected via N/O contacts of RL1 along
with a bell or an alarm.
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