A very cool project, where LED respond to the music. It is a very basic application of an NPN transistor in Common-Emitter mode. Go ahead and get this made by you.

Step 1: Components Required

1. TIP-31C (NPN type power transistor)- 2 Nos.

2. Audio jack - 1Nos.

3. LEDs

4. 9V Battery or equivalent DC power supply

Step 2: TIP31C - Transistor

The TIP31C is a base island technology NPN power transistor in the TO-220 plastic package with better performances than the industry standard TIP31C that make this device suitable for audio, power linear and switching applications.

The pin configuration is a shown in the figure.

Step 3: LED and Audio Jack Pin Configuration

1.The anode and cathode of the LED can be easily identified Anode(Longer leg) and Cathode(Shorter leg). Still confused? follow the LED schematic

2. Similarly, follow the Audio Jack's schematic.

Step 4: Circuit Connection

The circuit connection is to be made as shown in the schematic. You can even connect the LEDs to the single channel, this will reduce the number of transistors required. However, stereo effects can only be possible with the dual channel (Right and Left) right!

Step 5: Implementing in a Room

With very few LEDs, if you implement in the room it won't be a real fun. So, I insist to use the LED strips in the place of LEDs.That would be much effective and really fun.