Stepper Motor used as sensor

Other Hardware Sensors
1

Ok, So i have this new project idea where i had a dial that would be controlled by a stepper motor. basically to reset the dial to position zero programatically. Once this has been reset i want to know if the dial has moved, in what direction and how many step (hopefully the stepper motor can detect 100+ steps per rotation.)

Using the stepper motor through a driver is simple enough, i've done that a half dozen times. the kicker however is to sense when the dial has turned based on feedback from the stepper motor.

It is my understanding that a stepper motor can have current applied to move the motor, but the reverse should be true (albeit to a much smaller degree). I'd like to avoid a hall effect sensor, optical encode or other sensor, to simplify the components.

Has anyone tried something like this? can i even get feedback from the stepper motor? I should, but i haven't tried to scope a stepper motor, but i'm trying to avoid buying a stepper before i know this will work. Also i'd like it if this motor could run rather quickly(1+rps). any suggestions on a good inexpensive motor that would fit these requirements? just to be clear it does need to rotate continuously in either direction.

2

Nope. Need an encoder.

3

does anyone know of a stepper motor with an encoder optical or otherwise built in. i have very limited resources for turning my own parts so coupling a encoder to a SM would be cumbersome. Any suggestions? I figure if i have to use an encoder my best bet for coupling with fewest parts would be to add an optical encoder to the SM shaft (at least the disk) and then having it move over the actual sensor mounted to the side. What do you think?

4

A stepper motor works fine as a relative shaft encoder. It will act as a generator if you rotate the shaft and the two coils output out-of-phase AC signals, similar to a quadrature encoder. The AC voltage depends on the speed of shaft rotation, so you will need some way to reliably convert that to pulses.

For absolute positioning you need to either have an index location and switch, or an absolute shaft encoder.