Audio-Driven Flashing LEDs

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This is a circuit that flashes an LED or LEDs in time with music. You hook up an audio source to the circuit, and the LED(s) light up brighter when it is louder, and are off when it is quiet. This rave-like effect is achieved through the use of just one transistor.

Parts List

The following parts are in the following schematic from left to right:

  • 12V DC power supply (I used an old wall-wart from the Boneyard.)
  • Resistor/LED combo (I used one high-intensity blue LED arrays that Brad donated.)
    • If you need help figuring out your resistor value for the LED(s) you've chosen, use this resource.
  • TIP31c Transistor (I bought them here)
  • Audio input (In this schematic it is listed as a TRS jack.)


There is a problem with the file if you are reading this alt-text, contact Jared about it at

Known Issues

One main problem with this circuit is that a standard line-level audio signal from a portable media device or a computer is not loud enough to drive the transistor to light up the LED(s), so I used an old pair of desktop computer speakers (also from the boneyard) to act as an amplifier; so that the amplitude of the audio signal the system received would be loud enough to light the LED(s).

  • I would like to fix this circuit with an op-amp built-in so a separate amplifier is not necessary.


If you're attempting to tackle this project, Feel free to stop by the Learn-a-thing or whenever and ask Jared about it if you need help!

This project appropriates some instructions from this instructables.

Jared built this circuit on 10/29/15.