HP-25 Co-luminous segments

[teenix]

(04-08-2022 06:44 AM)Tom Flatterhand Wrote:  Before I do that, did you see that I added to the previous message in this thread? There I made an assumption. Can that be so?

Those Classics used a different approach to controlling the display. Externally, the Woodstock approach is simpler. !2 digits, one digit active at any time, and also only 1 LED segment ON at anytime. 40uS on x 8 segments = 320uS x 12 digits = 3.8mS per full refresh.

The 8 segments are output from the ROM0 chip and the ACT controls the Cathode Driver.

Have a look at the HP-29C repair manual starting from page 2-1. Same display deal for all the Woodstocks.

If you don't have it...

https://literature.hpcalc.org/community/hp29c-sm-en.pdf

cheers

Tony