I have a BKA30DR5 stepper motor that operates at 15mA. I want to drive it using an A4988 stepper motor module. I've previously driven stepper motors that use much higher currents (around 1A) successfully with these modules so I figured I'd use it again.
I set the reference voltage on the module according to this method, combined with the information on this page. The current sense resistors on the board read R100 so my formula for calculation the reference voltage is 0.015A * 8 * 0.1 Ohms = 0.012V. That's such a low voltage that I have trouble setting it using the trim pot: I have to make minuscule adjustments once I get below the 0.02V range and even then it just goes from 0.02V to 0.005V seemingly at random. I guess the trim pot becomes inaccurate at that very very low range.
How do I get the module to provide the correct reference voltage to the motor? I guess the motor uses so little power that I could technically skip the module entirely and connect it directly to the pins on the Arduino but I'm not sure if that's safe for the arduino considering back EMF. Perhaps it's also possible to set the module to a higher reference voltage and then use a separate resistor to drop the voltage to the correct amount but I'm not sure if that even works with stepper motors, nor where between the module and the motor the resistor(s?) should be connected.