Hector Martin wrote:

> If you go with the on/off idea, you might want to have the PIC track the
> AC wave and turn it on/off at the zero-crossing, 

You also have to worry about inertia of the motor flywheel.

> and doing timing based
> on pulses. If you start chopping pulses in half it might end up causing
> some drift (I guess it depends on how accurate you want to be).
> 
> You could also just have a fast switch and do per-pulse on/off. Same
> idea, but instead of generating the pulses yourself you just chop the AC
> wave.

Why not just divide the AC by 10 and use capacitor coupling to drive the motor
at a lower voltage (to prevent coil saturation. After all, the point is to reach
a certain current (flux) so 1/10th the frequency means 1/10th the voltage needed.
The problem with induction motors (as used on most totalizers, is that you need a
certain DI/Dt to get the needed back EMF off the rotor, so Dwayne's suggestion of
using pulses is probably correct.

Robert

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