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. I wasn't sure if the card edge style connectors would work, but they came out nearly perfect. After a light sanding with a flat file, they easily fit into the terminal blocks. There are a few things I want to tweak for version two, but feel free to make modifications yourself. The design files are on Github as well as some example code.