I took my first stab at designing and having my own PCB manufactured for a mechanical clock I'm trying to build. At the moment I'm currently stuck trying to debug the 7 x MCP23017 devices on my I2C bus. I picked up an oscilliscope and added a level converted between the RPi and my PCB, but I feel pretty lost as I'm a complete novice and have no formal background in electronics. This article provides a lot of useful information for someone like me! Online all you usually get are single MCP23017 implementations, nothing too complex.