Finally found some time to work on the little COSMAC computer kit I picked up a few months back, Lee Hart’s “Membership Card”.
I’ve wanted to experiment with the RCA 1802for a few years but never got around to designing my own machine around it, so when I found the ‘Card I thought it would be a nice way to get started working with the chip.
As it turns out, the kit is wonderful! It comes with copious amounts of printed documentation and the parts are all nicely labeled. There was maybe one unlabeled resistor which is exactly the right amount (process of elimination and all that).
The only real complaint I have is that the pi out for the seven-segment LED displays was certainly designed by a masochist. For some reason the holes are staggered instead of being in straight lines like the pins on the package. The assembler must bend the pins ever so slightly out and in for each row in order to make them fit. Bend, fit, bend again, for 16 pins on two devices.
For me this was torture as my eyes struggle seeing small shiny things so I had to use a loupe the entire time. When I received the kit I was disappointed that only two digits were supplied but by the time I finished this step I had completely reversed my position…
Sadly, I didn’t get to light it up quite yet. I accidentally used a wrong transistor on the CPU board and destroyed it trying to desolder it. Luckily I noticed before attempting to apply power, but of course it has to be the one type I don’t have spares of so I’m stuck for a bit while I track one of those down.
I’m super excited to play with this thing. I haven’t toggled-in a program since I was a child, and my memory of that is pretty foggy. Aside from nostalgia this project has contemporary value as well. I’ve been studying how I might apply asynchronous circuits to JS/OS and while the COSMAC isn’t exactly that, it can be stopped and single-stepped without ill effect. So aside from being a great post-apocalyptic pocket computer, I’m hoping to use it to experiment with ways of writing software that can be frozen in time.