=20

	The thermistor we use is NTC thermistors, accuracy line 2322 640
3/4/6....=20

	and here is a snippet of code (with a text schematic of a resistor
network at the end -- assuming my mail client doesn't destroy this
email!=20
 // Call this with   temp_lookup(ADCValue) where ADCValue is the raw
value from ADC port
 // The 2.2 is the resistor on the pullup / 10     *(our resistor is
22k)*
 float temp_lookup(int ADCValue) =20
 {
  float ohms, a, b;
  ohms =3D 2.2 / ((1024/(float)ADCValue) -1);
  a =3D log(ohms);
  b =3D 1.0 / (3.354016e-03 + 2.569355e-04 * a);     =20
  b -=3D 273.2;          =20

	 return  b;   //   ADC
  |
  |
  |
  / Thermistor
  /
  |
  |
  |
  0v  BODY { font-family:Arial, Helvetica, sans-serif;font-size:12px;
}=20
 On Thu 28/03/13 3:11 AM , "Harold Hallikainen"
harold@hallikainen.org sent:
  I used a precision thermistor, a precision resistor and (as I
recall) a 20
 bit delta sigma ADC in this thermometer: http://www.gla-ag.com/ [1]
.. Since
 the supply to the top of the resistor was also the ADC reference, a
 precision reference was not required. Linearization is done with a
table
 and linear interpolation.
 Harold
 --=20
 FCC Rules Updated Daily at http://www.hallikainen.com [2] -
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 opportunities available!
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Links:
------
[1] http://www.gla-ag.com/
[2] http://www.hallikainen.com
[3] http://www.piclist.com/techref/piclist
[4] http://mailman.mit.edu/mailman/listinfo/piclist
--=20
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View/change your membership options at
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