alvarop
Hello!
Your show-and-tell talk reminded me of a similar project I did while in high school, around 1973.
Together with the two other nerds in our high school class we built an accurate digital timer (not a clock!) using very similar 7400 circuitry. The timer did not use a 555 IC (those didn't exist AFAIR) but we used the AC coming out of the transformer in the power supply, tapping the rectified but unsmoothed voltage. In Europe AC is 50 Hz, so rectified this was 100 Hz, which made the counting easy. (EDIT: In the Twitter thread I saw this technique is called Schmidt trigger.)
Instead of 7-segment displays (which existed but were expensive so I had no experience with them) we used BCD for the readout using 6V 0.05W lightbulbs. I don't recall what we used for drivers, probably a simple transistor per bit. We had four BCD "digits", allowing us to measure times up to 100 seconds, with 0.01 second precision.
The lab assistant helped by making a sturdy case, and the physics teacher (our favorite!) used it to help lower classes measure the force and acceleration of gravity. (And teach them counting in binary at the same time. :-)
Ah, nostalgia! Feel free to close this after reading.
