Andrew Sowa designed this notched PCB in Kicad to control a rely board via I2C:

16-Channel I2C Relay expander

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.

source: http://andrewsowa.com/blog/2016/5/15/16-channel-i2c-relay-expander-v10

source: http://andrewsowa.com/blog/2016/5/15/16-channel-i2c-relay-expander-v10

source: http://andrewsowa.com/blog/2016/5/15/16-channel-i2c-relay-expander-v10

The design files and source code are available on GitHub:

FRM16_Relay_Module_I2C_Controller

Junes-PhD has shared the board on OSH Park:

FRM16 Relay Module I2C Controller