I came across this funny little guy on ebay. Anybody have one of these, or remember them from back in the day?
It's a very simple circuit, and they actually included some decent photos of the front and back:
Good enough to see most of the circuit, and infer the rest, so I drew up a schematic
and built it on a breadboard:
And it worked great. does exactly what it says.
Looking at the clips that the original uses to attach to the keyboard encoder connector, does anyone know what they're called or who makes them?
Also, I found evidence of at least one other board out there that looks like it works pretty much the same way, https://68kmla.org/bb/index.php?threads/identifying-cards-in-a-ii.41462/
I never had one, but I remember seeing them advertised back in the day.