I am using a Nema 17 stepper motor SY42STH47-1684A that has a rated voltage of 2.8V and a Rated Current of 1.68A. I connected the VMOT and the GND of the DRV8825 to a laptop power supply rated at 15V 5A and set the Vref of the DRV8825 to .84v before powering off and connecting the motor leads.
When I plug the laptop power supply back in powering the motor everything is OK until I turn on the power to the Raspberry Pi. It appears as soon as the Raspberry Pi’s 3.3v pin goes high and powers the SLP and STEP pin of the DRV8825 the stepper motor starts humming and juddering.
Any help with what could be wrong would be very much appreciated.
Could you post some pictures that show all of your connections as well as some close-up pictures of both sides of the DRV8825 driver? A video of the problem would probably be helpful as well.
There is a lot going on in the tutorial you linked to (e.g. there are multiple programs using different microstepping modes). Are you running one of those programs when you get the unexpected behavior? Note that the Raspberry Pi might do some unexpected things with the GPIO pins when booting. You might try testing it separately from your code by removing your current connections to the STEP and DIR pins, then manually connecting and disconnecting the STEP pin to 3.3V repeatedly while the DIR pin is connected to ground to see if the motor steps at all. You will probably want the driver in full step mode (e.g. the MODE# pins disconnected or driven LOW) for this test to make it easier to see the steps.
By the way, it looks like that tutorial uses a 48 steps per revolution motor, and your motor is 200 steps per revolution, so you might need to account for that if you are not already doing so.
