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#!/usr/bin/python
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#
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# Creates a C code lookup table for doing ADC to temperature conversion
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# on a microcontroller
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# based on: http://hydraraptor.blogspot.com/2007/10/measuring-temperature-easy-way.html
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"""Thermistor Value Lookup Table Generator
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Generates lookup to temperature values for use in a microcontroller in C format based on:
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http://hydraraptor.blogspot.com/2007/10/measuring-temperature-easy-way.html
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The main use is for Arduino programs that read data from the circuit board described here:
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http://make.rrrf.org/ts-1.0
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Usage: python createTemperatureLookup.py [options]
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Options:
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-h, --help show this help
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--r0=... thermistor rating where # is the ohm rating of the thermistor at t0 (eg: 10K = 10000)
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--t0=... thermistor temp rating where # is the temperature in Celsuis to get r0 (from your datasheet)
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--beta=... thermistor beta rating. see http://reprap.org/bin/view/Main/MeasuringThermistorBeta
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--r1=... R1 rating where # is the ohm rating of R1 (eg: 10K = 10000)
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--r2=... R2 rating where # is the ohm rating of R2 (eg: 10K = 10000)
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--num-temps=... the number of temperature points to calculate (default: 20)
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--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
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"""
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from math import *
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import sys
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import getopt
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class Thermistor:
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"Class to do the thermistor maths"
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def __init__(self, r0, t0, beta, r1, r2):
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self.r0 = r0 # stated resistance, e.g. 10K
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self.t0 = t0 + 273.15 # temperature at stated resistance, e.g. 25C
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self.beta = beta # stated beta, e.g. 3500
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self.vadc = 5.0 # ADC reference
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self.vcc = 5.0 # supply voltage to potential divider
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self.k = r0 * exp(-beta / self.t0) # constant part of calculation
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if r1 > 0:
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self.vs = r1 * self.vcc / (r1 + r2) # effective bias voltage
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self.rs = r1 * r2 / (r1 + r2) # effective bias impedance
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else:
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self.vs = self.vcc # effective bias voltage
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self.rs = r2 # effective bias impedance
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def temp(self,adc):
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"Convert ADC reading into a temperature in Celcius"
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v = adc * self.vadc / 1024 # convert the 10 bit ADC value to a voltage
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r = self.rs * v / (self.vs - v) # resistance of thermistor
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return (self.beta / log(r / self.k)) - 273.15 # temperature
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def setting(self, t):
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"Convert a temperature into a ADC value"
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r = self.r0 * exp(self.beta * (1 / (t + 273.15) - 1 / self.t0)) # resistance of the thermistor
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v = self.vs * r / (self.rs + r) # the voltage at the potential divider
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return round(v / self.vadc * 1024) # the ADC reading
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def main(argv):
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r0 = 10000;
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t0 = 25;
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beta = 3947;
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r1 = 680;
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r2 = 1600;
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num_temps = int(20);
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try:
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opts, args = getopt.getopt(argv, "h", ["help", "r0=", "t0=", "beta=", "r1=", "r2="])
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except getopt.GetoptError:
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usage()
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sys.exit(2)
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for opt, arg in opts:
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if opt in ("-h", "--help"):
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usage()
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sys.exit()
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elif opt == "--r0":
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r0 = int(arg)
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elif opt == "--t0":
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t0 = int(arg)
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elif opt == "--beta":
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beta = int(arg)
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elif opt == "--r1":
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r1 = int(arg)
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elif opt == "--r2":
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r2 = int(arg)
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if r1:
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max_adc = int(1023 * r1 / (r1 + r2));
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else:
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max_adc = 1023
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increment = int(max_adc/(num_temps-1));
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t = Thermistor(r0, t0, beta, r1, r2)
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adcs = range(1, max_adc, increment);
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# adcs = [1, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 130, 150, 190, 220, 250, 300]
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first = 1
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print "// Thermistor lookup table for RepRap Temperature Sensor Boards (http://make.rrrf.org/ts)"
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print "// Made with createTemperatureLookup.py (http://svn.reprap.org/trunk/reprap/firmware/Arduino/utilities/createTemperatureLookup.py)"
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print "// ./createTemperatureLookup.py --r0=%s --t0=%s --r1=%s --r2=%s --beta=%s --max-adc=%s" % (r0, t0, r1, r2, beta, max_adc)
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print "// r0: %s" % (r0)
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print "// t0: %s" % (t0)
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print "// r1: %s" % (r1)
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print "// r2: %s" % (r2)
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print "// beta: %s" % (beta)
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print "// max adc: %s" % (max_adc)
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print "#define NUMTEMPS %s" % (len(adcs))
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print "short temptable[NUMTEMPS][2] = {"
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counter = 0
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for adc in adcs:
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counter = counter +1
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if counter == len(adcs):
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print " {%s, %s}" % (adc, int(t.temp(adc)))
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else:
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print " {%s, %s}," % (adc, int(t.temp(adc)))
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print "};"
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def usage():
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print __doc__
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if __name__ == "__main__":
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main(sys.argv[1:])
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