I’ve been sitting on a couple of LED arrays/panels/boards for a few months, wondering what to hook up to them. I built them to test a shipment of LED’s, but I’d love to give them a more creative and pleasant duty. They’re each made up of 40 ultra-bright white LEDs arranged in eight groups of five. Here’s what they look like:

Each row of five can get pretty bright, but I never got around to building a driver board utilize them. (Partly due to the face that I didn’t want to do PWM dimming on 16 channels with what I had at the time.) The five LEDs in each group are wired in parallel. The eight groups are arranged in common-cathode fashion, which means there are eight “power” wires and one ground wire on each board. Here’s a close-up of the end of a boards:

I received some new prototyping PC board recently, and it seemed a perfect opportunity to build a driver board for these panels. I decided to power each channel with a 2n2222 power transistor, with an 18 ohm current limiting resistor. This puts about 80 milliAmps into each LED channel, which should be quite bright. I drew up a sample circuit for one half of one of the boards’ drivers:

This circuit is basically repeated four times on the driver board. The outputs go to a 2×4 set of pins that the panels can plug into. The signal inputs (base connections) to the transistors are headers. Here’s how it turned out, top and bottom:

I’m really happy that I was able to fit everything and maintain a low profile. This lets me stack another board on top of this one with the control circuits. The next step I’m working on is a set of shift registers (74HC595) to control the panel signals. This could lead to controlling all 16 channels with just a few outputs of a microcontroller. I’m not far on that board yet:

Anyway, hope you enjoyed the photos. I’ll get some images/video of the LEDs in action once I have the top board a bit more populated.