World’s Smallest Color Organ

The first thing you will need is the materials and tools. All of both can be bought at Jameco.com

You will need:

an SMD LM339 (bought in packs of 5);

SMD 1KΩ and 470Ω resistors (bought in packs of 100 each);

SMD 0.1uF, 0.22uF, and 1uF capacitors (bought in packs of 100 each); (Note: I did not have any SMD 1uF capacitors, and I instead used a through-hole version, but it looks far better to use all SMD caps.)

a collection of resistors or three 500K potentiometers (these cannot be SMD; they must be through-hole);

SMD red, yellow, and blue LEDs (bought in packs of 100 each);

SMD breakout board for 16-pin SMD ICs. Note: this is NOT a prototyping board; it is designed to be soldered to.

Offboard components:

3.5mm jack, or other line-level audio input

2 x 3v coin cell battery holder, 4 AAs, or any other power source over 5V

Resistor, capacitor or other through-hole leads if you want to pin it on a shirt or lapel

Non-momentary switch (any kind, basic power switch)

Optional: power indicator LED

Recommended and needed tools: (Note: the file and screwdriver in the picture are not useful for this project; they are for another.)

Soldering iron (needed)

Wire cutters (usually needed)

Wire strippers (usually needed)

Tweezers (recommended)

“Fun tack” or “blue tack” used for hanging posters. It also helps hold down the components, as in Colin Cunningham’s SMD video (recommended)

Solder (needed)

Magnifier loupe, glass, or other magnifying device (recommended)

Now, solder everything according to the schematic in picture 2. You only need one LED per channel, however, not four. Also, if you are using fixed resistors to control the frequency response, replace the 500K pots with your choice of resistors. Ignore the 3906 transistors. Connect the LEDs directly between positive and the comparator outputs. This will put about 6V across the LEDs, but the chip cannot deliver enough current to damage them, and the voltage is only applied for a tiny fraction of a second.

If you notice that the chip is too hot to touch, stop soldering and let it cool down. Too much heat will damage the chip.

The recommended component layout is shown in the next step.

Recommended component layout.

After soldering the circuit, just add a 6-12V source (I used a 9V battery for its compact size), and an audio input. Since the audio positive is connected to power ground, you will only need three input wires.

I suggest covering the circuit in epoxy or hot glue to protect it.

Troubleshooting tips:

If the LEDs stay on steadily, check the audio connection to the circuit itself. Also, make sure the pots or large resistors are connected between the “+” comparator input on the 339 and power “+”.

If nothing happens, put an LED with a resistor across the power pins on the LM339 to ensure that power is reaching it. Also, turn up the input volume, or increase the value of the resistors between the LM339 inputs and power “+”.

If nothing happens, test your batteries first. Even a perfect circuit will not work without at least 3-4V, and it needs current. A 9V battery producing 4V will not power this, but a 3.6V battery producing 3.6V will.