-----Original Message-----
From: Lawrence Lile <lilel@TOASTMASTER.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Tuesday, May 04, 1999 11:05 AM
Subject: In System Calibration


>I've been dreading a project that may require in-system calibration.
Here's
>the scenario - I'm using some cheap, poor tolerance thermistors and
>potentiometers in a controller.  I have a number of these built up, and
>found their behavior changed quite a bit from unit to unit, ostensibly
>because of tolerance variations.  (I'm not really sure)
>
>I could tighten the tolerance by spending money, but the circuit must be
>absolute minimum cost.  So I'm imagining a system that:
>
>1.  Does a final check on resistances in the circuit  (and maybe a quality
>control check too?)
>
>2. Calculates two or three constants based ont he resistances in the
circuit
>
>3. Creates the proper code (would it have to COMPILE or just modify the
>right bits in a hex file?)
>
>4. Squirts the program into a PIC either in- circuit or just before
>insertion
>
>It sounds really complex and capitol-intensive.
>
>Has anybody worked with these before?  Is there commercial equipment that
>does this task automatically?

dip the thermistor in icewater/boiling water and start autocalibration with
a dedicated input or unusual combination of already used input pins

store the calibration value in eeprom

Peter