[GreenKeys] Affordable current loop adapter

[John Nagle]

I've designed and built one that's powered from a USB port.

https://github.com/John-Nagle/ttyloopdriver

I and three others have built this. But I wouldn't recommend
that approach today. It's over-designed. Requires surface
mount soldering, and the USB to serial part it uses, the
Silicon Labs CP2102, is deprecated. The CP2102N, the
replacement, won't work; it won't go down to 45 baud.

New designs will probably have to have some dumb CPU of their own.
It's very hard to find a device that has a 5-bit 45 baud serial port
any more.


				John Nagle