This article shows you how to make a 12 V light bulb that blinks with music input.

I thought of this idea after reading the following article:

https://www.instructables.com/id/Sound-Light-Robot/

Alternative articles are shown here:

Resistor and capacitor circuits:

https://www.instructables.com/id/Simple-Sound-Lights/

https://www.instructables.com/id/Crazy-Sound-Light/

Transistor circuits:

https://www.instructables.com/id/One-Transistor-Sound-Light/

Op-amp circuits:

https://hackaday.io/page/8959-simple-op-amp-sound-light

Comparator circuits:

https://dr-mark-glickman-circuits.webnode.com/

Supplies

Parts: transistors - 3, 120 ohm resistor - 3, 1 kohm resistor - 2, 12 light bulb (LED or incandescent) - 2, voltage regulator (LM317 or LM337) -2, heat sink (for voltage regulator), 470 nF capacitor - 2, matrix board, solder, insulated wire, 1 mm metal wire.

Tools: pliers, wire stripper, soldering iron, music source.

Optional parts: audio socket.

Optional tools: multi-meter, USB Oscilloscope.

Step 1: Design the Circuit

I have drawn the circuit with https://easyeda.com software.

The signal entering the transistor bases increases the transistor current, reduces the transistor collector voltage, thus dragging the output voltage down.

Calculate the total potential voltage across R1 and R2:

Vr1r2 = (R1 + R2) * Vadj / R1

= 2* Vadj