Hey Derek,

excellent advice....thanks :-) PWM makes a lot of sense, and that
circuit looks like i may actually be able to get that soldered *grin*

What are you dong with those tape motors

Cheers,
d

On Dec 1, 2008, at 6:33 PM, Derek Holzer wrote:

> Ooooooorrrrrrr....... use the PWM out of one of your oscillators to
> control the MOSFET transistor directly. That would be the most simple
> solution, then you could get rid of everything to the left of R9 in
> that
> schematic, as that is the part which makes the square wave PWM. In
> that
> case, just use your separate 12V PSU connected via the protection
> diodes
> to the "D" of the transistor.
>
> Still doesn't do reverse, but that's where the H Bridge would come in.
>
> best,
> d.
>
> Derek Holzer wrote:
> > I've been using this PWM circuit to run motors:
> >
> > http://solorb.com/elect/pwm/pwm1/
> >
> > Main thing is to use a transistor to do the actual PWM instead of
> > running too much current through the opamps themselves. You could
> > replace the potentiometer for the PWM with a vactrol of some sort
> and it
> > should work fine for VC. It's something I mean to try myself. I
> run six
> > of these circuits and six 12V cassette player motors from a 12V
> 0.3 amp
> > wall wart, so the draw isn't that heavy at all. You don't want the
> PWM
> > mixed in with your synthesizer grounds however, since it's super
> noisy!
> > So yes, use another PSU, but it doesn't need to be so heavy duty.
> >
> > Unfortunately, this circuit doesn't do reverse. For that, you will
> need
> > to investigate an IC called an H-Bridge, which can switch from
> positive
> > to negative. Most datasheets of an H Bridge will give a simple app
> for
> > this. You should also look at the documentation of the Arduino
> project
> > for simple PWM motor control circuits, there should be one with an H
> > Bridge in there as well.
> >
> > best!
> > Derek
> >
> > Denis Gökdag wrote:
> >> Hi all,
> >>
> >> i want to build myself a little VC electro motor, you know, one of
> >> these little model-plane 12V motors but with VC RPM. It's not
> supposed
> >> to track V/oct cleanly, just be somewhat predictably controllable
> via
> >> a CV.
> >>
> >> I'm not much of an electronics genius, but i figured that i would
> use
> >> a non-inverting amp based on an OP-amp to buffer the CV, then use
> the
> >> output as the voltage to drive the motor (the second connector of
> the
> >> motor being connected to ground). Obviously, the Op-amp would be
> >> powered by the a-100 +/-12 V, so the design should be able to
> output
> >> -12...12V to drive the motor (with the negative voltage reversing
> >> direction).
> >>
> >> Does that sound about right
> >>
> >>
> >> cheers,
> >> denis
> >>
> >>
> >> ------------------------------------
> >>
> >> Yahoo! Groups Links
> >>
> >>
> >>
> >>
> >
>
> .
>
>