I missed this on the livestream and I haven't watched it yet, but I will do, because when I first saw these videos, for someone brought up on microprocessors, finding out what you can do only with diodes was a revelation.
David Peaker
2023-10-23 23:05:44 +0000 UTC
This made me think of the old HP decade frequency counters. They came out around 1962, I believe, and I saw several in 1969 when I visited the nuclear reactor Michigan State University used to have.
You probably don't need to do a video on them: they're expensive, and there are several good videos out there (mostly by Usagi Electric). But you should definitely know about them, if you don't already, because the circuit design is very clever, bordering on bizarre.
Here is some reference information:
Operating and Servicing Manual for Model AC-4A and AC-4B Decade Counters
http://www.hparchive.com/Manuals/HP-AC-4A-4B-Manual.pdf
Restoring an HP 521A Frequency Counter
https://www.youtube.com/watch?v=RxWDU-G_gJs&t=32s
In-depth Look at the HP AC-4G Decade Counter
https://www.youtube.com/watch?v=WrBPVVKvWfE
Enjoy!
Lynn
