Willem van der Jagt was watching Dave Plummer’s video in which he made a clock in 6502 assembly for his Commodore PET. Having an Apple II clone, he wanted the same for his computer. However, Dave has a real-time clock in his Commodore, but Willem doesn’t have one in the Apple.

I started thinking about how I could do a similar clock for my Apple 2 without such a card. I didn’t really care about it keeping time with the computer turned off because I won’t rely on this to know what time it is. I mostly just want to see it work.

While looking for ideas, I realized the solution was right in front of me: the pendulum clock that belonged to my grandparents, hanging on the wall right behind my Apple.

Willem discovered an inductive proximity sensor to use to detect the swings of the pendulum. Then some hardware to count the sensor pulses inside the computer using an interrupt. Finally code to display the time on the CRT.

Check out all the project details on GitHub.