Establish Common Ground and Verify Motor Power

Tools Required: Multimeter, jumper wires.

Safety Precautions: Power off the Raspberry Pi and the external motor power supply before making any wiring changes to avoid short-circuiting the Pi's GPIO pins.

Steps:

1. Locate the GND pin on the external motor power supply and connect it to a GND pin on the Raspberry Pi using a jumper wire to ensure a common reference potential.
2. Ensure the positive terminal of the external power supply is connected to the VMOT pin of the stepper driver and the negative terminal is connected to the driver's GND pin.
3. Power on the external supply and the Raspberry Pi.
4. Set your multimeter to DC Voltage mode. Place the red probe on the driver's VMOT terminal and the black probe on the driver's GND terminal.
5. Verify that the multimeter reading matches the required operating voltage of your stepper motor (typically 12V–24V).
6. Attempt to operate the stepper motor; successful rotation confirms that the common ground has enabled the driver to accurately interpret the Pi's logic signals.