Reference voltage

I am using DRV8825 Stepper Motor Driver. I want to set the reference voltage to 0.2 but using potentiometer the lowest that I could get was 0.8 vol. I am using 5v power supply for the driver and 8v to the motor. I did the exact thing based on this youtube video ( Setting the Current Limit on Pololu Stepper Motor Driver Carriers - YouTube ).
Here is the picture of my circuit.


It is a little hard to tell what is going on in your picture; are you using double sided headers on your driver? Can you post some close up pictures of your driver, including pictures that show your solder connections?

The minimum operating voltage (supplied to VMOT) for the DRV8825 is 8.2V, so do you have a higher voltage supply you can test with?

Also, just to confirm, please make sure that your A-Star is powered when you try to adjust the current limit so that it is providing 5V to drive nSLEEP and nRESET high to enable the driver.

- Patrick