Ah, yes.. one caveat in BOTH cases.  With the commutation method, you
have to apply clean DC to the motor to see the effect.  The PWM would
have to be cleaned up, probably with an LC filter, so that you can see
the results.

With V feedback, I found that the only way to measure voltage with any
accuracy was to read the A/D just before the transistor on time begins.
I rolled a PWM in software with a twist in it to allow the A/D to
execute before on time began.  This was no big deal, since the PIC PWM
does not go down to the 50 to 100 Hz that you want for motor PWM, so I
had to do software anyhow.

Roman Black wrote:
> There is another simple way that I have used with
> good results on a few occasions. Small DC commutated
> motors develop a sharp back-emf spike with every
> time the brush breaches a commutator segment.
> With a normal 3 segment com and two brushes this
> makes 6 evenly spaced spikes per rotation.

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