mike@D-M-G.DEMON.CO.UK wrote:

>In message <819601260.23810.0@vms.dc.lsoft.com> PICLIST@mitvma.mit.edu writes:
>> I am looking for a way to use the pic to control a resistor in a circuit
>> (to use as a microcontroller controlled variable power supply).  Would
>> anyone have any ideas how?  Thanks in advance.
>>
>You could look at multipliying DACs. Maxim do some 12 bit 8 pin
...
Haven't read the original post, but since I hope that the PIC will be part
of the feedback loop, what about a LED/LDR approach, with PWM and a filter
cap to drive the LED ? Slower, and you need some feedback, but cheap.

Or even an ordinary LED-Transistor optocoupler - again with PWM and
filtering for the LED.

Just gives me an idea - what about a switched mode power supply in this way
? Although output filtering at high currents may be a bugger. Any ideas how
high one could push the switching frequency with a PIC and PWM regulation ?
No additional parts except power transistor (and necessary drivers) and
output filter, adjustment via two buttons (up/down), and a LCD dot-matrix
as display :-)

Would need a 17Csomething, though, with built-in ADCs.

Bye
  Markus