gunrunnerjohn posted:...Obviously, if we can come up with something with sufficient flexibility that doesn't require the uP, that would likely be a better plan, easier for anyone to build and use.…
Recognizing that this is delving deep into the "HOW", here's a bare-bones, minimalist implementation of the back-up light application. No microprocessor, no Wi-Fi, no programming, etc..
I was looking at the DCS Port tester tool developed here on the OGR forum. It occurred to me that this board has a dual-timer circuit on it. So I thought why not something like this where timer #1 generates a ~1/2 sec pulse to send a reverse-light-ON RF burst...and timer #2 generates a ~1/2 sec pulse to send a reverse-light-OFF RF burst. The timer chip on the tester board is the 74123 type device which conveniently has the ability to trigger on either the "rising" edge or "falling" edge of an input signal. So timer #1 would trigger when the locomotive tail-light turns on (rising edge) and timer #2 would trigger when the locomotive tail-light turns off (falling edge). The DCS tester tool already has a 5V DC power supply chip that converts track level AC voltage.
Yes, this is only relays a single locomotive light to a remote receiver. But nothing stops multiple receivers from listening to the single transmitter. So, for example, multiple lighted passenger cars could turn their lights ON/OFF slaved to the interior light of the locomotive.
Yes, there are some loose ends to mop up. But the all-in cost for the transmitter side would be well under $5. Obviously the dual-timer functionality (and much more) could be implemented with a microcontroller, Arduino, etc..
Hence, I'm still interested in hearing more about the "WHAT" of this idea. That is, while I'm all for a "semi-universal" widget, I wonder if a simple one-function device could solve a good number of applications! 
