Harold, thanks. As far as a quadrature encoder, I wanted to know the
absolute position. For example, what if there was a power failure when the
oven was set to 300F. How would I know where the dial was set? I could use
battery backup but I want to keep this simple and fairly `bullet proof'. I
like Lawrence's approach using a Pot.

   I also like his PID method which should be easy to implement with some
tuning. The proof is in the pudding and it sounds like his results are
pretty tasty ;-)

   - Tom

At 05:25 PM 5/6/99 EDT, Harold Hallikainen wrote:
>        I kinda like the use of quadrature encoders with a display.  The
>use of the rotary control has a nice feel to it while the display gives
>precision in setting.  A quadrature encoder should be less expensive than
>one with a binary output and takes less pins on the PIC.  Also, you can
>do some dynamic scaling on it so that when you turn it quickly it makes
>big changes in the setting, while turning it slowly makes small changes.
>        Also, probably cheaper than an encoder is just a pot!  Run it
>into an analog input on the PIC and do the A/D.  Only uses one pin!
>        I think on/off control is fine for this application.  You may
>want to experiment with how much hysteresis to put in the loop.  If you
>do go for something fancier, a simple proportional control driving phase
>control of the solid state relays seems pretty straightforward.  Just
>don't try listening to the radio while baking!  Of course, you CAN move
>all the way to PID control.  I'm not sure what this will get you.  You
>state the heat losses through the insulation are low, so the 'droop" due
>to the heating load should be minimal.  Even with proprtional control,
>you have to "tune" the loop (or at least keep the loop gain down) to keep
>the oven from oscillating.
>
>Harold
>
>Harold Hallikainen
>harold@hallikainen.com
>Hallikainen & Friends, Inc.
>See the FCC Rules at http://hallikainen.com/FccRules and comments filed
>in LPFM proceeding at http://hallikainen.com/lpfm