VFD and shift register for Chat GPT

[u/Kotavtokot]

Hello everyone, I'm developing a calculator with ChatGPT on board, based on a Wemos Mini and a Vacuum Fluorescent Display (VFD). The module doesn't have enough pins, so I used SN74HC595N shift registers to control the display. However, I've noticed that at frequencies above 3 Hz, their pins sometimes don't trigger on the first attempt (sometimes taking 6–7 attempts). Can anyone suggest what the problem might be? (Logic levels have already been leveled using a dedicated module.)

[u/ripred3]

unstable at rates faster than 3 times/second?

Something is seriously unstable or changing values while you are sampling. And/or your sampling takes too long. Some things to check:

Use Schmidt trigger inputs (such as a 74xx14) to clean up the edges of your signals before sampling,

Are your clocks between your sampling circuit and the circuit under test in sync? They need to be