We’ve been using the A6276 LED driver quite a bit in our recent projects. It interfaces easily with microcontrollers, drives 16 LEDs, and you don’t have to worry about a bunch of drop resistors.

The downside is that we use it for a lot of different projects — some of them we don’t / can’t move around easily. Or maybe we have an installation (like the garage light bar), and you don’t want to take it down / sit in the garage while debugging new effects.

After the lightbar experience, I decided that we needed a “development” board of sorts. Something that would allow Evelyn to test out her programs, without having the piece sitting in her office. Here is the end result:

I used (tedious) point to point wiring, but that’s okay, since this is for our personal development use. The board is about 2″ x 3″.

The A6276 driver (24 pins) sits in the middle. Along the bottom are 16 square 5mm-ish red LEDs. I used these square ones because they fit the best (picked them up at Tanner surplus in Dallas a while back). As you test your programs, the LEDs light up. They are in order (1 though 16).

Along the left and right edges are 4 sets of 4 pin Molex connectors. These are the standard .10 on center connectors we use for connecting our small scale electronics. I wanted to have these on the board so that the project (ex. a mask) could be tested on the dev board. This means you don’t need to wire up a whole new A6276 every time you want to just play with something (that may or may not work out). The LEDs and the externals are in parallel, so you’ll get a drop in current, but that’s okay for debugging our projects.

In the upper left there is a three pin connector for connection to the microcontroller (in our case, usually an Arduino / Atmel 168 chip). The three lines are data, clock, and latch.

To the upper right of the chip you have the inbound power connector — everything, chip and LEDs, runs at 5 V. In the upper right there are 4 sets of 2 pin connectors. These are power connection points for the outboard LEDs. In some of our projects we have one common power source, so you’d just use one pin. In other projects we have multiple power feeds (necessary when the sets of LEDs being driven are located away from each other, or if the design is modular).

Near the power connector (partially hidden) is the current reference resistor. I use the term “reference resistor” on purpose. This is NOT AN LED DROP RESISTOR. This is a resistor that works with the A6276 to determine output current. Most LEDs are safe at 20mA, so I used a 1K resistor. Resistors are often off by a factor of +-10% at lower ratings, so it’s a good idea to measure its actual value on a good multimeter. In my case, the resistor was 970 ohms, which gives me 20mA of current. (For the A6276 you calculate output current as I = 18.76 / Rext. Other driver chips will be different — look at your data sheets!)

I also put a header-type pin in there for the downstream serial data (near the white wire).

This morning Evelyn finished soldering up some header pins to the twisted wires and connected it to an Arduno. And, ta-da, it worked. Hopefully this will make development with the A6276 LED Driver easier.

If you are using these drivers, I highly recommend you make your own version.