RoBonnet v0.2 was design to do a full hardware test, except for the power supply part (more on that later).

Starting top/left you can see connectors for TTL serial (5V with level shifters because the Pi is 3.3V). encoder inputs (3.3V-5V tolerant), 2 channel DRV8833 h-bridge (5V), 8 PWM channels (5V signals with 5V power), I2C (3.3V-5V tolerant without pull-ups), Pi connector, and power input (6V to 24V).

The board also hosts a BNO055 IMU, a BMP280 pressure/temperature sensor and an INA219 power monitor.

Note that all the I2C devices on the board (and the external connector) are attached to the i2c-3 bus on the Pi. If you've never heard of this, it's the software-based i2c implementation available as part of the Linux kernel. This is used rather than the hardware i2c implementation because that's just broken and has been on every Pi ever. The Broadcom chips used in Pies have a bug preventing them from working with i2c devices requiring clock stretching; and the BNO055 needs this. This bug is ancient and why it's never been fixed in new firmware is a mystery. Thankfully Linux's soft i2c device comes to the rescue.

This prototype was a complete success with everything working as expected (I know!).

The final unknown is the power module which is new territory for me; I've always used other people modules in the past. My first attempt will be with the MP2315; wish me luck.