Good thread, I actually had a semi-related question I needed to ask.
Currently, it's the power switch that chooses the trainer jack direction between PPM in and PPM out. With the switch off it is an output, with the switch on it's an input. However, from what I can see it's actually controlled by software, with signal SIMCONTROL on pin PG4 of the AVR (taken from FCC schematics).
Now, would you be open to extend/replace that power-switch-controlled behavior to a menu setting, as an extension to the discussed behavior?
Here's why:
I have modded my trainer jack (which is actually stereo), and wired (switched) power onto the unused contact. I fly FPV, and this allows me to plug my video goggles with integrated head tracker into the trainer port. With a single cable, I power the video goggles from the radio's battery, AND send head tracker info to the radio. The perfect, clean, highly portable setup. I can plug the jack with the radio off (no power on the jack, which is good as when you insert a TRS plug it usually creates temporary shorts), then turn the radio on, which powers the goggles and turns the trainer port into an input to accept the head tracker's PPM.
That's perfect. But now, that convenient port could also be used for an RF module, with power of course (FrSky DHT-U for channel 9-16??). But this would require the jack to be powered (switch ON), with the trainer port set to PPM out.
I have already tried other solutions (using direct, unswitched battery power onto the jack, even if bad), but while it doesn't cause damage the trainer port somehow won't work at all anymore, either as input (channel values are jumping all around) nor as output (nothing), unless I unplug the battery, insert the jack, then plug battery, where it then works normally. It seems the 4066 somehow doesn't appreciate some power it might receive for a split second when the jack is inserted.
I have even rewired the jack to apply power to the tip contact that is less likely to cause shorts rather than the orignally free middle contact, but no change. I left it that way as it has the advantage that in case someone plugs a mono jack into my TX all it would do is short the PPM line instead of the battery - much less risky. Less so for the student TX that would get battery power into its PPM line, but that's not my problem anymore
So, in summary, it would be nice to have a "soft" setting to choose trainer port direction, and thus being able to use a powered output in both directions
