I wanted to see if I could build an 8 bit binary counter using only 555 timer chips for all the logic gates necessary.
I knew that there was an SR latch inside each 555 timer. I got to thinking maybe I could string two of them together, with some other glue logic, and make a master-slave JK flip flop that could act as a 1 bit counter. Not wanting to bury the 555s under a ton of other TTL or CMOS logic gates, I found ways to build the other needed logic gates out of either yet more 555 timers, or from diode-resistor logic.
The design was created in KiCad, and a one bit counter was prototyped on a breadboard as proof of concept. A clock circuit for driving the counter was also built using another 555 timer chip, of course.
Once the prototype was working, I cleaned up and condensed the design enough to fit two 1 bit counters on a single breadboard. Then I just needed to string four of those two bit counters together to achieve an 8 bit counter.