>
> James:
>
>    Sounds like  you are already off to a very good start. I like your
> choice of a thermistor instead of a thermocouple or RTD, for your
> application the thermistor's sensitivity should make for a very tight
> control loop indeed, and you can't go wrong with your choice of
> microcontroller either.
>
>  If you don't have Microchip's Data Book and their Embedded Control
> Handbook, get them (602-899-9210). They are packed full of info and source
> code examples.
>
> In the Embedded Control Handbook you will find all of the code that you
> need to get you started. Using pieces from different examples you can cover
> everthing from Serial Input (both synchronous and asychronous) Application
> Note 510,547 to P.I.D. control schemes AN 531.
>

  Great!  I have both books you mention, but haven't gotten into either
  one of them yet.  I'm busy building ovens and oven control circuitry.
  But the next thing is to speak to the Analog Devices part with a serial
  interface GPIO card using HP BASIC.  Once we figure out how the part
  works, then we can get into PIC control loops.  Besides, it will take
  me that long to figure out how microcontrollers and assembly language
  work.  I looked up AN 531 and it looks like exactly what I need to
  understand PID controllers in assembly language.

> I am not familar with that Analog Devices chip Ad7714 but it sounds real
> interesting I am assuming since the chip gives you a serial output that
> signal conditioning, bridge excitation and A to D is handled on the chip.
> Is this correct? The Parallax book has both their instruction set and
> Microchips. So translation is easy. Also Parallax instruction set has some
> very useful routines
> for example their Compare instructions.


  The bridge excitation (reference voltage) is provided externally, but the
  signal conditioning (sigma-delta modulator style) is done by the AD7714
  with a serial output.


>
> I do not know if the Parallax assembler can take Microchip instructions,
> but either way you should have no problems. Make frequent use of Parallax's
> software simulator PSIM this is a very good troubleshooting tool. If you
> are going to do a lot of micro projects I highly recommend the Parallax
> Emulator available from DIGI-KEY.
>
> I can only guess at your knowledge of micro's and their related quirks but
> from your message and your choices so far you should have very little
> problems. Just dive right in and in no time you will find out that micro's
> are the greatest thing since sliced bread.
>
>                                 Joe West

  They certainly seem to be great little systems, so I'm anxious to get
  started with them.  Sounds like fun and a means of learning something too!
  Thanks very much for the head start on this, Joe.  I'll let you know how
  it goes.

  Jim Johnson
  jjohnson@hpl.hp.com