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Is there a test code that will allow me to use the ramps1.4 as a test fixture to set vref for on the a4988 stepper drive?

Posted by tm america 
I have been just adjusting the stepper drivers by the sound -low tech way.. But now I am wanting to do things the right way I am looking to set up a ramps 1.4 as a test fixture for settings the vref- max voltage of the a4988 or drv8825..so basicly I am looking for a test code that would allow me to do this? I am hoping for something that would do single step mode and keep the stepper driver energized so I could accurately measure the vref volts without it stepping..
You don't need to move the motor at all to set VRef . . . just a voltmeter. Heck, you don't even need 12v power - it is derived from logic power. Simply meter from the pot wiper to ground . . .

VRef is a static reference voltage used by the driver chip to compare against the voltage developed across the sense resistors. It is *NOT* derived from actual motor current . . .

- Tim

Edited 1 time(s). Last edit at 06/24/2015 08:33PM by tadawson.
I know I don't need the motor hooked up to test the vref voltage but I thought it had to have the stepper being pulsed ..in the pololu video of how to set the vref it show her having it hooked to a controller that is pulsing it and then she puts it in a different mode that makes it stay on so it can be adjusted...notcsurecwhich controller shexwas using or what the code looked like
Nope, it's a static setting that does not even require a motor to be connected. Look at the Pololu schematic - it's a pot from logic power to ground, with the wiper providing the VRef to the chip. Nothing in the circuit onthe output side whatsover.

They were likely showing the measurements of the output to show how it tracked, but that is not necessary.

- Tim

Edited 1 time(s). Last edit at 06/24/2015 11:20PM by tadawson.
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