I'm driving an APA102 LED strip from an ESP32. Both are powered from a single 12V power supply that is brought down to 5V using a high-current (10A) buck converter.
This works fine when I join the grounds of the ESP32 and APA102, and I get massive signal degradation without the joined (flickering lights etc.).
I know this is common practice when using multiple power sources (and I'm happy to keep the joined ground), but I didn't think it would be needed when both the ESP32 and LED strips are powered from the same power supply.
Why is the joined ground required in this configuration? Also, am I putting my ESP32 at any risk in this configuration?
It may be relevant that I'm powering the ESP32 dev board via its micro USB port using a custom USB cable that connects to the buck converter's outputs.