This board consists on a gps connected to a stm32 using the serial port (uart), and a magnetometer (hmc5883L). We convert the nmea data from the GPS to an i2c binary protocol in a similar way that the i2c-gps-nav project. The magnetometer is just included in the board, connected to the same i2c bus.

Why? The idea is to use this board in a multicopter. Having the magnetometer far away from everything else makes sense (magnetic interference from motors/battery/motor drives). Magnetic interference is specially important in big multicopters. We include the gps, because it is also usefull to have it well exposed away from everything else, specially other transmitting sources (telemetry transmitter, FPV video TX).

• We use a stm32f100c4 because it's extremely cheap.
• hmc5883L is a well known proven IC. Also 3D!
• We recommend a UP501 or a Venus GPS with 10Hz or more update rate.
• The board requires an external 3.3V regulated power supply, and a i2c 3.3v bus.
• We recommend to route this signals/power with a shielded cable.
• We followed the AN2586 manual to design this board.

• To program the stm32 we could use either JTAG or serial with http://code.google.com/p/stm32flash/ or http://tuxotronic.org/wiki/tutorial/stm32primer-flash-over-uart

• For the HMC5883L the capacitors of 4.7u and 0.22u must have a low ESR (resistance) < 0.2 ohms. 0402 smd capacitors may not work.