Fun with MAX7221 chips

Just a quick, short post here to show some stuff. I've been playing around with some seven-segment LED's and MAX7221 IC's; great fun. In collaboration with a colleague I've built a build monitor for our Jenkins CI server.

If you're interested in the source code: you can download it here
I'm using Atmel Studio 7 this time instead of the Arduino IDE. I had to roll my own UART interrupt handler in order to get everything to work correctly. The HardwareSerial class of Arduino just didn't cut it. I'm using AVRDude to upload the resulting HEX file to the Arduino.

It's three custom PCB's with a MAX7221 and seven segment display. The PCB's can be daisy chained. You can order the PCB's here. The bottom unit connects to an Arduino Nano. Vcc and Gnd connect to the 5V and Gnd pins. CLK to pin 13 (SCK). DIN to pin 11 (MOSI). CS to pin 9.

This is the schematic for a single PCB:

The PCB layout:

And a 3D render:

Yay, boards!

Doing some debugging:

It's working!

Combined with our CI Traffic light: