Translating Stepper motor driver outputs (A-,A+,B-,B+) back into clk,en,step

Question

I have a rather weird problem that makes it necessary to sense the four wires off of a bipolar stepper motor(A-,A+,B-,B+) and translate them back into the pins that controlled the stepper motor driver (clk,dir,step).

First i'll outline what I've tried:

1. mcp3008 ADC - This guy burned out right away. (I'm assuming because the stepper motor drivers for a nema17 output roughly 1.2amps per coil).
2. Looked for higher spec ADCs but I'm somewhat lost.

Questions:

1. Is there a better way to do this than using an ADC into a microcontroller?
2. What sampling rate would I need to "sense" the stepper motor drivers micro stepping and translate them back/ how to calculate this?
3. what ADC resolution would be acceptable/ how to calculate this? ex. 12bit, 16bit...
4. What voltage would be "safe" (I know a nema17 is approx 4V, but I'm worried that another stepper will be higher).
5. What ADCs are available that meet these spec? (above and below).
   • SPI or I2C
   • atleast 4 channels or (I can get four 1 channel ADCs).
   • through hole component package.

Thank you anyone who responds to all or either of my questions! This is my first post so I hope I was clear enough.

Answer 1

I would use optocouplers. You will need to calculate the values of R1 and R2 to get reasonable currents.

You will need to convert the PWM signals using software.

If you can turn off the microstepping, it will be easier.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

Just wanted to add that the ADC burned because its a bipolar motor driver and in its negative phase it tries to source current from the load ie. your ADC, burning it. You do not need an ADC to measure this voltage, you can get by using an octocoupler circuit as Mattman944 mentioned, which puts your microcontroller in parallel to the stepper driver, thus protecting any sensing equipment you have.