A recent project required me to control 48 channels of line voltage. I knew I needed some relays and more control lines so I went on a search for something affordable. Numato Labs had a nice 16 channel unit that was within budget and I was able to mock up a working unit by using a MCP23017 from Adafruit.
I wasn’t happy with the mess of wires and wanted something cleaner. Using Kicad and OSH Park, I made a small form factor surface mount unit. This reduced my supply wires and allowed me to daisy chain units for easier install.
The design files and source code are available on GitHub: