> This is actually part of a speed controlled motor controller. Know what I
> mean? I have to control the motor's voltage in order to keep its speed
> constant. This means I'll have to compare the speed with some reference
and
> then raise or lower the motor's voltage to keep its speed as I want
> (probably this reference will be adjustable). I should do all this only
with
> opamps, resistors, capacitors, etc.
> By black boxes, I meant I can't use Frequency-to-Voltage ICs, I should do
> one myself. And can't use any "digital devices", such as a
microcontroller,
> or a A/D converter...


DC motor?

Use PWM and measure the back EMF during the off periods.  A bit tricky
without a uC, I suppose.

Tony

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