Limiting output current for A4988


I am trying to set the limiting output current for the A4988 stepper motor driver but when I try to measure the VREF voltage, it keeps fluctuating (starts around 0.7V and goes down to 0.35V and back up, winding the potentiometer has no noticeable effect) and no definite voltage is measured.

I have connected it to an externally powered (AC-DC adaptor, output 12V @ 2A) arduino. I have connected the Vin port of the arduino to the VMOT, GND to GND and 3.3V port to the VDD port on the stepper driver (nomenclature as per minimal wiring diagram on the A4988 product page).

Is this expected behaviour? If not, am I doing something wrong?


P.S. I have also tested measuring a different source with the multimeter and it shows a good stable value.


The VREF voltage should not fluctuate, but it is hard to tell from your description what might be going wrong. Could you post pictures of your setup that show all of your connections including the solder joints? Could you also describe (or post a picture showing) where you are connecting the two probes of your multimeter? If possible, could you try powering the VMOT and GND pins on the driver directly and see if that helps?


Hey Claire!

Thanks for the reply!

I have not actually soldered the headers, instead just used them to pin the board into the breadboard (as visible in the attached image). I am connecting the common probe into the logic GND port of the driver board and the test probe on the potentiometer (I also tried to connect it to the VREF as referenced in your video, and as annotated in the attached image).

Could the issue be caused by not soldering the header pins? Unfortunately, I do not have the equipment available to power the driver directly at the moment.

[quote]Could the issue be caused by not soldering the header pins?[/quote]Extremely likely. All pins on a motor driver must be soldered. Also, never disconnect motor leads when the module is powered, or it could be destroyed.

You were right Jim! I’m able to set the current limit now! :slight_smile: