Introduction: Dancing LEDs

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Note - to build the project in this article you will need basic electronic skills including soldering. Use this information at your own risk; do not complain if it doesn't work for you.


I was amazed to discover that I could assemble an incredibly simple electronics circuit to hook up a set of LEDs to any audio output. Imagine having lights dancing in time with the music, or any other audio on your MP3 player, CD player, computer, home theater system, or any other audio source - for under $15.

Bright LEDs are popular decorations for vehicles and computers. They're inexpensive, watertight, and use a very small amount of power. They’re extremely easy to install. Mount the LED module with some sticky tape and string the wires to the fuse box. The LED module includes a current limiting resistor so it operates directly off of 12 Volts, the standard battery voltage on almost every automobile, motorcycle, and boat. Conveniently 12 Volts is also one of the voltages available inside desktop computers.

Step 1: How It Works

A common $0.98 transistor (NPN 2N3904) is all it takes to amplify sound levels to power the LEDs in time with your audio. Okay, you need two transistors if you want to do stereo. Add a stereo mini-plug, some wire, and about half an hour to put it together. Traditionally projects like this are assembled in an empty Altoids box, but that’s too large. I decided to use an empty tic-tac box for the case.

The circuit is so simple I didn't bother to etch a PC board, I just used point-to-point wiring on an ordinary perfboard cut down to fit inside the tic-tac box.

Step 2: Powering the Circuit

I decided to use this circuit with my computer, any audio which comes out of the computer's speakers makes the LEDs dance. But it can be hooked up to any ordinary audio source.

Many computer cases have front panel sound jacks. Fortunately both back and front jacks are powered at the same time. If your computer doesn't have multiple audio outputs you'll need an Y-cable to hook up your speakers and your circuit at the same time, or you can add a stereo mini-jack inside the tic-tac box and build a simple splitter as part of the circuit.

You can power the circuit with a 9 volt battery, or tap power from your computer’s power supply. I dug into my junk box and found an old computer fan which hooks up to a 5.25" power supply connector. I cut off the fan to reuse its power wires. To make it neat I mounted a small coaxial jack as a 12 Volt plug outlet on the front of the computer next to the headphone jack.

Step 3: Putting It Together

A transistor has three leads – the Base, Collector, and Emitter. The circuit is incredible simple - take the audio output and feed it into the Base of the transistor. The Collector is attached to the audio's ground and the ground for the power supply. The Emitter from the transistor goes to the positive line (red) on the LED module and its black wire (ground) is hooked up to the transistor's Collector.

In terms of wiring nothing is critical, just make sure the pins are connected to the correct locations, make sure there aren't any shorts, and double check the connections to make sure everything's correctly wired.

Obvious common sense rules - do not drive the circuit with too much volume (power) or you will burn out the transistor. Do not use more than 12 Volts. Make sure there are no exposed connections or points where short circuits can take place. Do not call me or complain if you can't get it to work properly. Do not blame me if something goes wrong. Make sure you eat all of the tic-tacs before using the box.

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Bio: Writer, engineer, techie. I've been using computers since the original Apple II in 1978 and have always been interested in technical topics. Check out ... More »
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