Just a bit more than a year ago I’ve started to work on a hardware idea as a challenge – a mini-PCIe form factor Arduino clone, the PCIeDuino. The inspiration was working with a bunch of embedded boards, especially the VIA VAB-600 Springboard, that had a mini-PCIe connector, but not that many accessories that can go in there. (Disclaimer, I work at VIA at the moment, though this wasn’t a work project). I thought it would be cool to put an embedded-grade microcontroller on these boards, mostly to expand the I/O capabilities.
Looking at the mini-PCIe specs, the connector has mandatory USB 2.0 lines so communication was solved. The area available, roughly 5.1 x 3.0 cm, is not too bad -more than how big the Arduino Nano is in comparison. The biggest challenge probably was that there are only 3.3V power lines available, and most example designs use 5V power supply.