The following documentation outlines a hardware design for a sensor package that is to be integrated with an autopilot. The system features a PIC16F microcontroller unit that interfaces with a gps module in addition to an accelerometer, a gyroscope and a magnetometer. These are all 3-axis sensors resulting in a 9 DOF IMU. The microcontroller communicates with the gps module and the sensors using I2C communication protocol. The gps module was designed to interface with a passive antenna through a SMA connector. The reverse polarity SMA connector selected has a 50 ohm impedance; therefore, the selected antenna must also have a 50 ohm impedance to avoid reflections on the transmission lines. The unit can be powered by an input supply greater than 6V, and uses a switching regulator to power all of the digital electronics. The design can interface with an autopilot unit through SPI protocol and also contains a programming port to interface with the PICKit3 programmer/debugger.
The files presented were generated using Altium Designer. The PCB that was designed is a two layer board with a grounded copper pour on the bottom layer. This ground plane reduces noise and in addition to supporting the antenna microstrip that was placed on the top layer. This microstrip was sized to have a 50 ohm impedance to match the 50 ohm SMA connector and thus prevent reflections on the line.