Few remarks:
- perhaps the polarity of the external power supply is wrong. Check if the chip on the ULN board is hot. Doublecheck the polarity. (*)
- on the ULN board, there are two contacts which - when connected - should enable the onboard LED to display the output state. . Place a jumper on these contacts, you should then see the pulses from the RPi.
- for a test disconnect the GPIO from the RPi. Connect the inputs of the ULN board to 5V from the external power supply, the onboard LED should light up.
- this stepper motor is incredibly slow. Takes prox 2048 steps per revolution. If your test code produces only few steps, then this will be barely noticeable. Produce more steps. I used some tape on the axle to connect a pointer to see any movement.
- If the steps produced by the RPi are fast, the motor will not follow. Keep frequency below 100Hz for first tests.
* check polarity with a multimeter. If you don't have, then use your LED-resistor combo and connect first to GND, +3.3V or RPI. Should light up. Then you know where plus, minus is of this LED-resistor-combo. Then connect to GND, 5V of your ULN board.
- perhaps the polarity of the external power supply is wrong. Check if the chip on the ULN board is hot. Doublecheck the polarity. (*)
- on the ULN board, there are two contacts which - when connected - should enable the onboard LED to display the output state.
- for a test disconnect the GPIO from the RPi. Connect the inputs of the ULN board to 5V from the external power supply, the onboard LED should light up.
- this stepper motor is incredibly slow. Takes prox 2048 steps per revolution. If your test code produces only few steps, then this will be barely noticeable. Produce more steps. I used some tape on the axle to connect a pointer to see any movement.
- If the steps produced by the RPi are fast, the motor will not follow. Keep frequency below 100Hz for first tests.
* check polarity with a multimeter. If you don't have, then use your LED-resistor combo and connect first to GND, +3.3V or RPI. Should light up. Then you know where plus, minus is of this LED-resistor-combo. Then connect to GND, 5V of your ULN board.
Statistics: Posted by ghp — Fri May 09, 2025 5:52 am