>         Brilliant Indeed!  Very punny! Anyway, I tried an analog regulator
> circuit using a lightbulb and optodetector for feedback. I also liked the
> RMS to DC conversion with isolation.  I was running proportional
> feedback. As I increased the loop gain, the whole thing started
> oscillating. I couldn't get tight enough control without oscillation.

Two sources of oscillation with the lightbulb approach is that the feedback
response is very non-linear with respect to the control output, and that the
light bulb has some lag.  I would think both these could be overcome by
sufficient damping and twiddling of other parameters in the PID control
loop.  Since the lightbulb's response is still faster than the heating
element under control, there should be room to slow down the over
corrections without cutting into the ultimate desired control response.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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