I’m building a cnc and I connected the DRV8825 to my CNC V.3 shield, and tried to measure the vref so I can adjust the current limit.
The problem is the I keep getting 12.39 [v] (this is exactly the PSU voltage, I checked) no matter how much I change the potentiometer
I checked all my 4 drivers, and it’s the same in all of them.
Where did you get your DRV8825 carriers? The VMOT voltage being shorted to the VREF via is a known problem of one of the knock-offs of our carriers, as discussed in this RepRap blog post. If you are not sure if your boards are genuine, you can post a picture of them here.
Additionally, if your CNC shield is meant for the A4988 carrier, you will probably need to use the wiring diagram shown in the “Key differences between the DRV8825 and A4988” heading at the bottom of the DRV8825 carrier’s product page to make it compatible.