Raspberry Pi Radio Tracker

This project is to make a Raspberry Pi based tracker (ARPS and/or RTTY) that can be used as a car based ARPS tracker or HAB Payload. I'm hoping to provide RTTY on a GPIO pin with accutate timing. The initial plans are to use a Raspberry Pi, UBlox GPS, Radiometrix NTX2 and Radiometrix HX1

The Raspberry Pi I'm using is an original Model B (256Mb Ram) but ultimately I want to use this on a Model A - possibly with some modifications to improve how it's powered. The Ublox and Radio Modules come from HAB Supplies.

At the start of this I wasn't sure whether it would be possible, sending RTTY data requires reasonably precise timing which may not be possible from a full OS like Linux. Previously the method used on the Pi for sending RTTY data is to use the UART to do the timing in hardware. This means the serial port is then shared by the radio and gps or you have to find an alternative method to interface to the gps.

After some investigation it appears that using a suitable method it's possible to drive a GPIO pin at around 20MHz (details are on the raspberry pi wiki) . RTTY requires a fraction of this speed so this looks possible. The only way to achieve this switching speed is via memory access to the hardware from C. Using Python or some of the simplier libraries give much slower speeds which may make this solution impossible.

My Source code for is is available on github. This is still a work in progress and has yet to be flight tested so may not work correctly.

Future expansions include use of DominoEX, adding SSDV and video streaming and/or moving some of the code into kernel space.