> On Mon, 17 Dec 2001, David VanHorn wrote:
>
> >
> > It's a 5 ohm motor, bipolar windings, running from a 6-8.5V supply.
> > The motor wants 0.5A.
> > I don't want to spend any more power than I must in driving it, since this
> > is a battery operated application.


Sounds like a small 17 frame or pancake stepper,
2.5v 0.5A. You are unlikely to get better than
2:1 with any chopper IC so it will probably
cost you 200mA+ from the battery anyway.

Unless you need high speeds, I think the best
solution is to switch to a 12v 200mA motor,
these still have decent speeds and torques at
6v, and being unipolar you only need 4 tiny
fets to drive the motor, you can use low sat fets
as you only need 4 and the circuit is simple
enough to wire.

Another good point about the higher inductance
12v motor is that you can implement simple slow
pwm from the pic outputs, good for low power
"hold" modes and stuff. Now you will probably tell
me you have to use the 2.5v motor? ;o)
-Roman

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