Here’s an incredible DIY LM555 Adding Machine that Alan Yates built, it can do adding and subtraction using method of complement numbers. This is like a digital version of old Adding machines people used to use back in the day.
The device was built with experimentation and modular testing in mind. Each decade ring is independently resetable and most multi-drop signals have diode isolators. Similarly carry-chain defeat is supported should I want to break up the accumulator into several parts. As such it uses a few more parts than are absolutely necessary. You could easily omit some of the diodes and resistors, but it would have been much harder to test each component in isolation without the current topology.
The only notable issue I had building it was a frustrating reset bug that turned out to be a rail sagging problem. Additional decoupling at the edge of the board cured it. The 555s really crowbar the supply while changing state and at reset all of them draw a rather large pulse of current.
It can count at up to 100 Hz reliably. I often tested parts of it using mains noise on my body or a signal generator to clock it.
Whoa! Take a look at the brains inside the LM555 Adding Machine, that’s 102 LM555 chips, all networked/soldered together by hand, one little mistake and poof! That’s called, “paying attention to details”, an important skill all circuiteers must have.
Want to build one? Alan Yates provided schematics as seen here:
If you are seriously about building one thought, better go check out the full instructions/descriptions at Alan Yate’s site.