createTemperatureLookup.py

#!/usr/bin/python
#
# Creates a C code lookup table for doing ADC to temperature conversion
# on a microcontroller
# based on: http://hydraraptor.blogspot.com/2007/10/measuring-temperature-easy-way.html
"""Thermistor Value Lookup Table Generator

Generates lookup to temperature values for use in a microcontroller in C format based on: 
http://hydraraptor.blogspot.com/2007/10/measuring-temperature-easy-way.html

The main use is for Arduino programs that read data from the circuit board described here:
http://make.rrrf.org/ts-1.0

Usage: python createTemperatureLookup.py [options]

Options:
  -h, --help            show this help
  --r0=...          thermistor rating where # is the ohm rating of the thermistor at t0 (eg: 10K = 10000)
  --t0=...          thermistor temp rating where # is the temperature in Celsuis to get r0 (from your datasheet)
  --beta=...            thermistor beta rating. see http://reprap.org/bin/view/Main/MeasuringThermistorBeta
  --r1=...          R1 rating where # is the ohm rating of R1 (eg: 10K = 10000)
  --r2=...          R2 rating where # is the ohm rating of R2 (eg: 10K = 10000)
  --num-temps=...   the number of temperature points to calculate (default: 20)
  --max-adc=...     the max ADC reading to use.  if you use R1, it limits the top value for the thermistor circuit, and thus the possible range of ADC values
"""

from math import *
import sys
import getopt

class Thermistor:
    "Class to do the thermistor maths"
    def __init__(self, r0, t0, beta, r1, r2):
        self.r0 = r0                        # stated resistance, e.g. 10K
        self.t0 = t0 + 273.15               # temperature at stated resistance, e.g. 25C
        self.beta = beta                    # stated beta, e.g. 3500
        self.vadc = 5.0                     # ADC reference
        self.vcc = 5.0                      # supply voltage to potential divider
        self.k = r0 * exp(-beta / self.t0)   # constant part of calculation

        if r1 > 0:
            self.vs = r1 * self.vcc / (r1 + r2) # effective bias voltage
            self.rs = r1 * r2 / (r1 + r2)       # effective bias impedance
        else:
            self.vs = self.vcc                   # effective bias voltage
            self.rs = r2                         # effective bias impedance

    def temp(self,adc):
        "Convert ADC reading into a temperature in Celcius"
        v = adc * self.vadc / 1024          # convert the 10 bit ADC value to a voltage
        r = self.rs * v / (self.vs - v)     # resistance of thermistor
        return (self.beta / log(r / self.k)) - 273.15        # temperature

    def setting(self, t):
        "Convert a temperature into a ADC value"
        r = self.r0 * exp(self.beta * (1 / (t + 273.15) - 1 / self.t0)) # resistance of the thermistor
        v = self.vs * r / (self.rs + r)     # the voltage at the potential divider
        return round(v / self.vadc * 1024)  # the ADC reading

def main(argv):

    r0 = 10000;
    t0 = 25;
    beta = 3947;
    r1 = 680;
    r2 = 1600;
    num_temps = int(20);
    
    try:
        opts, args = getopt.getopt(argv, "h", ["help", "r0=", "t0=", "beta=", "r1=", "r2="])
    except getopt.GetoptError:
        usage()
        sys.exit(2)
        
    for opt, arg in opts:
        if opt in ("-h", "--help"):
            usage()
            sys.exit()
        elif opt == "--r0":
            r0 = int(arg)
        elif opt == "--t0":
            t0 = int(arg)
        elif opt == "--beta":
            beta = int(arg)
        elif opt == "--r1":
            r1 = int(arg)
        elif opt == "--r2":
            r2 = int(arg)

    if r1:
        max_adc = int(1023 * r1 / (r1 + r2));
    else:
        max_adc = 1023
    increment = int(max_adc/(num_temps-1));
            
    t = Thermistor(r0, t0, beta, r1, r2)

    adcs = range(1, max_adc, increment);
#   adcs = [1, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 130, 150, 190, 220,  250, 300]
    first = 1

    print "// Thermistor lookup table for RepRap Temperature Sensor Boards (http://make.rrrf.org/ts)"
    print "// Made with createTemperatureLookup.py (http://svn.reprap.org/trunk/reprap/firmware/Arduino/utilities/createTemperatureLookup.py)"
    print "// ./createTemperatureLookup.py --r0=%s --t0=%s --r1=%s --r2=%s --beta=%s --max-adc=%s" % (r0, t0, r1, r2, beta, max_adc)
    print "// r0: %s" % (r0)
    print "// t0: %s" % (t0)
    print "// r1: %s" % (r1)
    print "// r2: %s" % (r2)
    print "// beta: %s" % (beta)
    print "// max adc: %s" % (max_adc)
    print "#define NUMTEMPS %s" % (len(adcs))
    print "short temptable[NUMTEMPS][2] = {"

    counter = 0
    for adc in adcs:
        counter = counter +1
        if counter == len(adcs):
            print "   {%s, %s}" % (adc, int(t.temp(adc)))
        else:
            print "   {%s, %s}," % (adc, int(t.temp(adc)))
    print "};"
    
def usage():
    print __doc__

if __name__ == "__main__":
    main(sys.argv[1:])