Hi, has anyone got, or can they point me to, info on torque control
of DC motors ?

I've got a 1/2HP 12V DC motor, PWM (10kHz) speed-controlled by
an IRF151 to ground. The F84 has 8 pushbuttons for Stop, Full and
6 fixed speeds, which works OK, but the customer's needs have
changed and would like better speed regulation under a now variable
load.

a) how do I derive an error signal from the motor ? (vaned opto ?)
b) should this be applied to the PIC via an ADC ?
c) could this be applied to the FET instead ?

One possibility I'm thinking of is compare the loaded rpm to the
unloaded at a particular PWM and look for a drop or rise. I wonder
if there's a simpler analogue way, but essentially the whole thing is
digital and mixing the two may be more trouble than it's worth.

Jinx