These two scope pictures stunned me before I realized the mistake that stunned me even more. The first picture show HEXFET Output in yellow, Logic High/Low Cyan and Purple and BEMF voltage in Blue. The upper picture is with no load and the 2nd is with a DC motor as load. Why do my High signal get disturbed ? Read on and get amused!
The answer baffled me. At first I was puzled by how weak the motor felt, but it was working and the controller with motor used 21mA – up to 40 if I held it. But, what was wrong? Looking at my test set-up I suddenly realized I was driving the motor directly from the STM32 High pin.
STM32 delivers up to 40mA per pin and this motor worked on 3.3V 21mA or something. Connecting it correctly it felt like a formula 1 in comparison.