I wanted to make a clock that changed from green to red over the course of an hour to reinforce time passing. I wanted to avoid watching "just one more episode" or neglecting chores until bedtime.

The quarter-round design makes the units modular, so I could put one in the corner of a window, two that form a rainbow, and four that make a circular clock.

I assembled my clock using some laser-cut pieces, but the same parts could be made with hand tools. I also soldered wires to the back, but the Dupont headers make it quicker to insert wires for a test-lab-chic look.

A clock is a solid application, but the display is more versatile. My code includes a useful function for converting ring-rotation into an LED address, so I hope it serves as a starting point for people.

The assembled board is ready to accept a connection to a 5V microcontroller. It has power on both header sockets so chaining them together is possible, but connecting voltage and ground back to a source will reduce voltage drop.

The trick to getting even color from the final product is adding spacers with light channels and a diffusing layer. My solution was to make PCBs with holes over the LEDs, stack one over the lit panel, add a layer of printer paper, and hold the paper with another of the holey boards. You can make those layers inexpensively out of wood or plastic using a CNC machine or laser cutter. I included CAD files for those components.

You can find my day-to-day build of this project on my blog.