This simple circuit shown int the schematic
diagram actives the switch using sound. We can use this circuit for
various applications, such as automatic (sound-controlled) disco light
or car’s LED light show. The Q1 amplify the
audio from mic. The R1 is used to adjust the peak of signal to greater
than about 0.7 volts, act as sensitivity adjuster.
Schematic Diagram of Circuit:
A certain level, the signal coming from microphone, after amplification by Q1, will trigger the SCR
and light lamp I1. If we change the lamp with a relay, then we can get a
sound-activated relay/switch, which can be used to control more
powerful / high wattage high voltage lamps. If we use a relay, place a
1N4007 diode in parallel with the relay coil to prevent the back-emf
from relay coil destroying the SCR.