This mains operated audio controlled running light can be used in discotheques. The lamps glow in running sequence as per the sound of music. Of the ten AC lamps, only one lamp permanently glows if there is no sound. When music is played, light starts ‘running’ through the lamps.
Audio Controlled Running Light Circuit
Fig. 1 shows the circuit for the audio controlled running light, while Fig. 2 shows the pin configuration of triac BT136.
The condenser mic converts audio signals into electric signals. Transistor T1 amplifies the microphone signals, which provide clock pulses to decade counter IC CD4017 (IC1). Preset VR1 is used to vary the signal level. The Q9 output provides reset signal to pin 15 of IC1. Divided-by-10 signals are fed to clock pin 14 of IC2, which is another decade counter. The outputs of IC2 drive transistors to provide triggering pulses to triacs. Triacs, in turn, drive the AC lamps. You can now see the lights running with the sound of the music.
Frequency-divider ICs CD4017 have been used here to reduce the audio to a noticeably low frequency. AC mains is rectified by diode D11, regulated by zener diode ZD1 and filtered by capacitor C4 to power the circuit.
The article was first published in January 2006 and has recently been updated.