I recently completed testing of the first prototype of the USB interface for DX Doubler using N1MM+ software. This was a rough prototype, so it isn’t pretty but it does seem to work fine. It currently handles RX and TX Focus, and STEREO for listening to both radios at once. There is an FTDI chip-based USB –> Serial converter that allows the interface to fully support PTT and CW keying on the single Serial port that is configured. I just need to add the BAND Data support. The interface uses the Open Two Radio Switching Protocol (OTRSP) that is used by several other SO2R Control boxes. This protocol, created by K1XM who generously shared it with the Ham Community, is supported by N1MM+ and several other Contesting Software Applications.
I used a cut-up LPT cable to connect the DX Doubler box to my interface. The interface uses and Arduino Board. In the photo, the Arduino is still tethered to the PC for power and uploading of Code. But there is no LPT and only the USB interface is now configured in N1MM+. I used an Intronix Logic Analyzer to scan all the data lines before connecting to a rig. Here is a shot of the Logic Analyzer screen.
Remaining work is making a 2nd prototype on a perfboard and testing with both radios.