I’m using a L293D to drive a bipolar steppr motor. The circuit I’m using is the standard (see attached image).
It seems to work, but to my surprise, if I don’t connect the GND pins 4,5,12,13 to ground, the engine still works !
Somehow, it must be using power from USB instead of the DC external source.
This is annoying as I was trying to measure the current that goes through the coils using a shunt resistor between GND line and pins 4,5,12,13.
Do you understand what is going on here ?