Did I blow up my new A4988 Stepper drivers?

Noobie here. Been cramming Arduino for 2 weeks with a starter kit. Got the stepper motor to work from the kit and just received two A4988 driver/carriers today. Eager to try out real world steppers.

First things first, I’m trying to set the Vref to limit the current. I have 12v on the Vmot, GND connected to ground on both the motor supply and the Arduino, and a 100µF cap across the 12v supply. 5v is from the Arduino, which is getting a feed from the 12v supply into Vin on the Arduino.

Everything measures fine, except the Vref on the via or on the surface of the pot. It measures between .013v and .018v (13-18 millldsf or so, going down to .006v (6millivolts). I’m supposed to be able to get it between 400 and 750 µv. No matter what I do, neither of my two Pololu A4988 Black Versions read anything else on that Vref pot or contact.

Did I blow them up? They still are getting 12v and 5v on the appropriate inputs. I was sure hoping to program these NEMA 17s tonight!

Any help would be fantastic!

Hello, rcarbaugh1.

It is not clear whether your boards have been damaged yet, but the VREF measurements you reported are unusually low. Can you post some pictures of your stepper motor driver that show both sides of the board as well as all of your connections? Some pictures showing how you are measuring VREF might also be helpful.

Also, I do not expect setting the VREF to the range you are suggesting to be practical. Voltages of 400 µV and 750 µV on VREF would correspond to current limits of 0.7 mA and 1.4 mA on our A4988 carrier. Why do you want to set the current limit so low? What stepper motor are you planning to use?

- Patrick