Some mains operated audio controlled light can be used in discotheques. The lamps glow in a running sequence as per the sound generated. When music is played, the lights start ‘running’ through the lamps. Ten AC lamps are connected to the circuit. Only one lamp glows at a time when there is no sound/music.
In this circuit a condenser mic is used which converts audio signals to electrical signals. These electrical signals from the microphone are fed to the transistor which amplifies the microphone signals and also provides clock pulses to the decade counter IC1 CD4017.A preset is provided to vary the signal level. As the decade counter has a total of ten counts, the pin corresponding to tenth count is connected to reset pin of IC1. One of the outputs of IC1 is fed to the clock pin of IC2 CD4017. The outputs of IC2 CD4017 drive transistors to provide triggering pulses to triacs.
The triac we are using is BT136, which is a 3-terminal device. In this triac, the first two pins are the terminal1 and terminal 2 and the third pin is the gate terminal. In this circuit, the triacs drive the AC lamps. In a triac when gate terminal is triggered then the triac turns ON which in turn powers up the load. Hence now we can see the lights running with the sound of music.