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
>>
>>
>>
>>
>

--
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 153:
"The inconsistency principle"