Sunday, 8 December 2019

Discrete TTL IC desk calculator

Today a memory of an old project that was a spectacular case of unfortunate timing came back to me. The British magazine Practical Electronics designed a desk calculator using TTL ICs. Unfortunately just as the 1st (or 2nd) part of 11 was published, MOS chips from Texas Instruments implementing an entire calculator came onto the market. And with better specs. The technology was obsolete even before it was published. PE decided to publish the project anyway for pedagogical benefit. Here is the cover of the July 1972 issue and the first 2 pages of that series:

The series has been archived here. It gets a mention in the EPE (Everyday Practical Electronics, two magazines having been merged sometime before) 50 year retrospective of 2014 (parts 1 and 2).

The component list is interesting. They weren't even Low power Schottky TTL packages, just standard TTL. Must have run a bit warm. 145 silicon diodes? Sounds like a microcode matrix.

I couldn't have built one anyway, it was far beyond my means at the time but it was interesting to read how the functions were implemented. I wonder if anybody other than the series author actually made one and wrote it up.

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