Problem fixed!
Just a quick recap:
I was struggling to get the PC Mobility Programmer software to communicate. I always had “COMMS INACTIVE”. I’ve tried 3 different VR2 modules and 3 different joysticks, 2 FTDI cables, 2 different versions of the PC programming software, and 4 computers. Also, with the help of this Forum, we tried many other fixes to get the communication to work.
Finally, I went to my friend who had all sorts of oscilloscopes and testing equipment. I took him my oldest and most beat up joystick which works, but never been used for programming. With the TTL-232R-3V3-WE cable, XLR cable, and resistor+diode mod, we monitored the cable signal. We found that the PC Mobility Programmer software was initiating the communication, but there was no response from the VR2 module. We eventually discovered that there was a broken TX/RX wire within this joystick cable. Can you believe that? However, that doesn’t explain why the other joysticks and modules wouldn’t communicate. We made a quick and dirty fix to the joystick cable and tested. We got “COMMS ACTIVE” and verified with the oscilloscope that the communications were going both directions, but the communication link was extremely unstable. The comms status in the software GUI was constantly switching from active to inactive.
We then played around with different resistances and found that 47K ohm is right on the very edge of degrading the communication signal to the point of instability or not functioning at all. My resistor pair was 48.4k ohm and was unstable with the old joystick. It would not function at all with the other joysticks and module combinations. We had a test box with different common resistor values to select such as 22k ohm, 33k ohm, 47k ohm, 68k ohm, etc… With this box in place of the programming cable resistor, we switched to 47k ohm and communications failed. Switching to 33k ohm worked with no instability. 22k ohm would not work. We also noticed that the rising edge of the signal was degraded with higher resistance which is likely the reason for the communication failure. Lower resistance made for a faster rise time and a solid digital signal. I went and tested the other joysticks and modules using the 33k ohm resistance in the programming cable, and they now communicate perfectly.
In conclusion, I believe that 47k ohm resistance for the VR2 is right on the very edge of having an unstable signal and may not function at all. Adding additional cable between the resistor and the XLR connector along with possibly dirty or corroded connections on either the joystick connectors or the VR2 connector may magnify the problem by adding resistance. I recommend a lower value resistor such as a 33k ohm.
To get a better idea of what value more suited for this purpose, I recommend someone perform a test. Use a potentiometer with a 22k ohm resistor in-line to prevent accidentally running the resistance too low. Then with the programming software running, slowly adjust the potentiometer until the comms indicator starts to switch between inactive and active (unstable). Then pull the potentiometer out and measure the resistance for both the bottom limit and again for the upper limit.
It has been a huge headache, but I just couldn't let this one defeat me. I wan't to thank everyone for quick responses to help.