Spike count without encoder, for small DC mottor

[tadashi]

Hello everybody,

i hope some of you already had the following issue: I have to find a solution to count the spikes resulted in a small DC motor commutation (The motor must be a brush/commutator type) without using a optical encoder, or a potentiometer attached to the shaft. Is there any IC that does the job? Or, does someone have some schematic that could help me with this?

I hope I will hear from you soon,
Tadashi

 

[dick_freebird]

I imagine that this would want some series sense resistance
or inductance, to make the discontinuity in current
observable. And what you get to work with probably depends
on the brush and commutation ring; one that only hits one
sub-winding at a time, ever (break before make), will
make large spikes while one that is always transferring
one winding's current to the next, make before break,
may only give a small detectable signal.

If you already have a current sense resistor then this
would be a "freebie" takeoff point or at least a good place
to put some 'scope probes and look for waveform features
that you could up-process to a reliable trigger pulse.
I think you want to begin with the realities of the motor,
and see what it wants to teach you.