I bought a pair of ND-100S SiRF-III UBS GPS dongles and some ATmega168 microcontrollers with the goal of adding GPS waypoint navigation and autopilot features to a model aircraft.
After receiving the dongles and opening them up, it turns out they’re quite easy to interface. On the back are some serial test points, bypassing the USB interface. (Which, as it turns out, is literally a USB-Serial converter.) The dongle outputs the NMEA data protocol, which means the output has specified standard outputs, and the dongle can be programmed to only output the information needed for the autopilot, which saves additional filtering/discarding of unnecessary information.
Next up was obtaining some accelerometers and building the auto stabilization part. Sadly, this project got shelved due to lack of time.
[2017 update: and it wasn’t long after that the quadcopter got ‘invented’ and not long after that commercial autopilot boards became extremely cheap and readily available, and re-inventing the wheel for autopilot wasn’t necessary anymore. Building an autopilot aircraft is still somewhere on the “to-do” list. Some day…