ArduPilot Hardware Archive
This is an archive of schematics for boards that ArduPilot supports. Note that ArduPilot supports many more boards than we have schematics for here, but this archive covers some of the best known boards to help with ArduPilot development
Also note that pinouts for all boards supported by the ChibiOS port of ArduPilot can be found here: https://github.com/ArduPilot/ardupilot/tree/master/libraries/AP_HAL_ChibiOS/hwdef