Weekend project. A cool circuit of LEDs flashing to music.

The LEDs are driven using the LS138 line decoder which is connected to the LS163 binary counter. The effect of the lights syncing with the beat of the music comes from that that the 555 timer generates a pulse at the same beat as the music, while the amp provides power to the counter and the line decoder, resetting them each time when the amplified signal goes LOW.