Digital Non-secure Voice Terminal Test Code and Switch PCBA Design Files.
http://robruark.com/projects/DNVT/DNVT_overview.html
This repo contains the PCBA design files for the DNVT test interface boards, four phone switches which run Nick Andre's code, and the crappy support code I wrote to initially reverse engineering DNVTs.
The Arduino code encodes and decodes Differential Manchester, and the Python scripts determine the codewords. There is also a Python script which decodes differential manchester based on a CSV capture from an oscilloscope. Example files are provided.