VREF Location for DRV8825 Current Limiting
Arduino Focuser, fully ASCOM complaint
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The directions for setting the current limiting pot to allow microstepping with the DRV8825 configuration refers to measuring voltage at "VREF". Is there something that I don't see, since I can not find a "VREF" anywhere on either the Nano board or the 8825 board? I am attempting to set up the NEMA bipolar stepper for 1/8 stepping. Help.
Thank you,
Jim
It is found on the REF pin, often this appears as a small round solder pad on either the top of underside of the board. You will need a multimeter and power must be be applied to the board.
Do the following with half steps.[do this ONLY when not connected to the telescope - make sure the stepper is not connected to the telescope! ]
Another way is to power the board, set the position to 0, then enter like 6000 and click the goto button. Wind the pot all the way anticlockwise, which the motor should stop. Then very slowly turn the pot clockwise until you see the motor start to turn
If the steps is reached, just set the position to 0 and then type in 6000 for the position and click Goto again,
Slowly turning the pot, when you see the stepper start to move ok without jerking, then slowly turn no more than 1/8th clockwise from that point. Then it should be close enough. If you go too far then there will be too much current and the motor will run hot. You should use no more than 12V external power.
On some boards clockwise might be anticlockwise,
Once set, then switch to 1/8th stepping and repeat the 0 then 6000 goto. The motor should run smoothly without missing steps (a missed step will be a sudden jerk which you will be able to feel or hear). If there is any of this, you might need to ever so slightly turn it a little more. Be careful as a little turn can make significant changes in current,
Last edit: brownrb 2016-01-02
And it is best to use a ceramic or plastic screwdriver when adjusting the pot. I would suggest a plastic knitting needle which has the end filed down to look like a screwdriver.
http://www.my-home-fab.de/Documentations/Technical-descriptions/DRV8825-Adjust-Stepper-Current/en
shows where the ref solder pad might be,
Another user did this.
The 8825's must be connected to 12v external power and the motor. Measure the reference voltage between system ground and the top of the potentiometer (the part your philips screwdriver touches). I simply clipped the red lead of my Meter to my screwdriver. Note: the pot can go round and round, and it is remarkably sensitive.
Please note that you WILL need to calculate the expected VREF if you are using different stepper types which are not rated at 400mA, or using a different voltage source (not 12V)