As Raspberry Pi sales continued to rocket we started to try and define what an add-on board might look like (with most of these discussions taking place in the Premier Farnell canteen over numerous cups of coffee or by squeezing in time-zone friendly conference calls with the US team). We all knew that we wanted something using a similar form factor to the Arduino / chipKIT but we also wanted it to mate with the Raspberry Pi’s I/O connector.
We also wanted to differentiate ourselves from mainstream Arduino boards so we chose to use a 28-pin dip PIC32 MCU. Using a DIP MCU kept the product well within the hobbyist domain (how many folk can solder fine pitch parts on their kitchen table?!). Price, needless to say, was also an issue so to keep the board as low cost as we could; we used as many Microchip components as possible.
Downloading the completed sketch code onto the chipKIT Pi was always going to be done via the UART on the Raspberry Pi – this would keep the Pi USB ports free for other things. This meant we could conveniently sit the chipKIT Pi over the Raspberry Pi, as long as we positioned the I/O socket on the chipKIT Pi correctly.
The PIC MCU would feature a boot loader and would be placed in boot loader mode by pressing certain buttons on the chipKIT Pi. The idea was that this would create a nice neat solution that would also be reasonably rugged – but of course we had to consider exactly how this was done without compromising on the boards compatibility with chipKIT / Arduino shields. To help this, various voltage regulators were added to the board, pretty much replicating the circuit on the chipKIT UNO. Other changes included looking at status LEDs as well as providing access to the other Raspberry Pi I/O. Just as on other chipKITs, we provided ICSP (In Circuit Serial Programming) pins to allow the MCU to be reflashed onboard. The other major change made was in adding a USB connector with the eventual aim of allowing the board to work within MPIDE on a Windows platform.
With the ideas flowing and momentum pushing forward, the design brief was fired over to Embest for board design and the manufacture kick off.
Mike McGlade – Senior Regional Channel Manager