The bit-banged Clock waveform of a found-online TM1637 library for STM32 is ugly and only shows the clock getting up to 1.6V (3.3V supply) for “High”…but bit banging at TM1637_BIT_DELAY = 40 works, and “10” doesn’t (not enough time for the signal to reach the lower threshold of digital 1.)
No blinky (1.2V):
Blinky (1.6V):
Found culprit:
