I'm trying to connect an ESP32-CAM to a 3d printer using a serial connection. When powering the ESP from the 5V rail on the 3D printer(and using 3.3V zener diodes between tx, rx & gnd), everything works fine. The ESP expects 3.3V on the serial pins, hence the diodes.
Common ground not shown.
Then when I try to run the ESP32 from its own 5v power supply, I cannot establish a serial connection, regardless of whether I connect the gnd from the 5v from the 3d printer with that of the ESP power supply. In fact, the ESP doesn't function then.
PS: the ESP has its own power since it should trigger a relay to cut power to the printer.