I am venturing into the space of designing expansion boards for Raspberry Pi's. I have done this for Arduino boards but RPi's are a different beast.
From personal experience I have already had problems with damaged UART pins on the RPi and I am keen on finding ways not to repeat his experience.
Considerations I have come up with:
- The IO pins are sensitive and needs protection. It can be as simple as Zener Diode to ensure the voltage stays at 3.3V and a current limiting resistor. Example Circuit
- The GPIO pins are 3.3V , can source about 16mA and can only do about 50mA in total. The 3.3V rail is limited to 50mA and not suited for powering external components. Instead the 5V rail with +500mA can be regulated to supply more
- The GPIO's are not suited for hot-swappable expansion boards and need to be powered down before installed.
- External Power supply for extension boards are recommended.
- Expansion boards can stacked but the limited current on the 3.3V rail could be an issue.
Considerations in question:
- ESD - How well does a Rpi deal with people handling it.
Any other suggestions will be mush appreciated.
Extra Links worht looking at: