Now let’s be clear, this is not the first time we’ve come across this idea, there was a breadboard ... LTSpice model of a NAND gate implemented with 555 and diodes From there it was a simple ...

With the two diodes reversed and a 910 Ohm resistor removed, a NOR gate is created. The next step was to build a S-R latch using the NAND gates and inverters, which holds some basic memory.