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#!/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)
"""
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:])
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