Electronic – how to construct stepper motor driver

How is motion feedback produced? The first time I tried to program a robot with motion feedback (decades ago), I failed to consider that motors could coast a little bit when they were powered off, and so attempting to move the motor e.g. 23 pulses would sometimes cause it to move 23 and sometimes 24. That could cause the next move to be processed incorrectly. To solve such problems, one should (1) slow down the motor as it approaches its destination, and dynamically brake it when it reaches its destination, to avoid or minimize overshoot, and (2) use a constantly-modified quadrature encoder to determine when overshoot occurs, and adjust the next move request based upon the overshoot (each count of overshoot should shorten the next move by a count if it's in the same direction, or increase it if it's in the opposite direction).

I like using the closed-loop Hall effect LEM current transducers for this sort of application. They're a lot cheaper than a genuine current probe for a scope (only about $20 or $25), have excellent accuracy and bandwidth from DC up to a couple hundred kHz.

The particular one I've linked has a +/-6A range, but you can put a couple loops through to get +/-3A full scale. Just feed it a reasonably clean +5V and Robert's your uncle.

If you want to make more of a project of it, you can offset the output with differential output between the LEM and a 2.5V reference, or actually subtract it with an op-amp and bipolar supplies, but for most purposes, just adjusting the scope zero will do the trick.