For our final Hardware Software Integration (CprE 483) project at Iowa State University, we contacted the SSCL (Space Systems and Controls Laboratory) in search of a project that might be useful to them.

SSCL frequently launches high altitude balloons with payloads that transmit data to the ground station using HAM radio. This data is ASCII text in AX.25 packets from the on-board sensor packages. The data is transmitted using the Bell 202 standard. The ground station HAM radio system has a sound jack, like that used on personal computers and stereo equipment. Our Modem project's goal is to connect to this jack, sample the analog sound data, convert that data to binary and output the data as ASCII text to a serial port where it can be logged on a personal computer.