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157 lines
6.1 KiB
157 lines
6.1 KiB
#!/usr/bin/env python |
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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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https://en.wikipedia.org/wiki/Steinhart-Hart_equation |
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The main use is for Arduino programs that read data from the circuit board described here: |
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https://reprap.org/wiki/Temperature_Sensor_v2.0 |
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Usage: python createTemperatureLookupMarlin.py [options] |
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Options: |
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-h, --help show this help |
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--rp=... pull-up resistor |
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--t1=ttt:rrr low temperature temperature:resistance point (around 25 degC) |
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--t2=ttt:rrr middle temperature temperature:resistance point (around 150 degC) |
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--t3=ttt:rrr high temperature temperature:resistance point (around 250 degC) |
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--num-temps=... the number of temperature points to calculate (default: 36) |
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""" |
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from __future__ import print_function |
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from __future__ import division |
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from math import * |
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import sys,getopt |
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"Constants" |
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ZERO = 273.15 # zero point of Kelvin scale |
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VADC = 5 # ADC voltage |
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VCC = 5 # supply voltage |
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ARES = pow(2,10) # 10 Bit ADC resolution |
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VSTEP = VADC / ARES # ADC voltage resolution |
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TMIN = 0 # lowest temperature in table |
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TMAX = 350 # highest temperature in table |
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class Thermistor: |
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"Class to do the thermistor maths" |
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def __init__(self, rp, t1, r1, t2, r2, t3, r3): |
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l1 = log(r1) |
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l2 = log(r2) |
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l3 = log(r3) |
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y1 = 1.0 / (t1 + ZERO) # adjust scale |
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y2 = 1.0 / (t2 + ZERO) |
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y3 = 1.0 / (t3 + ZERO) |
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x = (y2 - y1) / (l2 - l1) |
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y = (y3 - y1) / (l3 - l1) |
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c = (y - x) / ((l3 - l2) * (l1 + l2 + l3)) |
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b = x - c * (l1**2 + l2**2 + l1*l2) |
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a = y1 - (b + l1**2 *c)*l1 |
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if c < 0: |
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print("//////////////////////////////////////////////////////////////////////////////////////") |
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print("// WARNING: Negative coefficient 'c'! Something may be wrong with the measurements! //") |
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print("//////////////////////////////////////////////////////////////////////////////////////") |
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c = -c |
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self.c1 = a # Steinhart-Hart coefficients |
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self.c2 = b |
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self.c3 = c |
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self.rp = rp # pull-up resistance |
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def resol(self, adc): |
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"Convert ADC reading into a resolution" |
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res = self.temp(adc)-self.temp(adc+1) |
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return res |
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def voltage(self, adc): |
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"Convert ADC reading into a Voltage" |
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return adc * VSTEP # convert the 10 bit ADC value to a voltage |
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def resist(self, adc): |
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"Convert ADC reading into a resistance in Ohms" |
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r = self.rp * self.voltage(adc) / (VCC - self.voltage(adc)) # resistance of thermistor |
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return r |
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def temp(self, adc): |
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"Convert ADC reading into a temperature in Celsius" |
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l = log(self.resist(adc)) |
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Tinv = self.c1 + self.c2*l + self.c3* l**3 # inverse temperature |
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return (1/Tinv) - ZERO # temperature |
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def adc(self, temp): |
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"Convert temperature into a ADC reading" |
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x = (self.c1 - (1.0 / (temp+ZERO))) / (2*self.c3) |
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y = sqrt((self.c2 / (3*self.c3))**3 + x**2) |
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r = exp((y-x)**(1.0/3) - (y+x)**(1.0/3)) |
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return (r / (self.rp + r)) * ARES |
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def main(argv): |
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"Default values" |
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t1 = 25 # low temperature in Kelvin (25 degC) |
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r1 = 100000 # resistance at low temperature (10 kOhm) |
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t2 = 150 # middle temperature in Kelvin (150 degC) |
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r2 = 1641.9 # resistance at middle temperature (1.6 KOhm) |
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t3 = 250 # high temperature in Kelvin (250 degC) |
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r3 = 226.15 # resistance at high temperature (226.15 Ohm) |
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rp = 4700 # pull-up resistor (4.7 kOhm) |
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num_temps = 36 # number of entries for look-up table |
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try: |
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opts, args = getopt.getopt(argv, "h", ["help", "rp=", "t1=", "t2=", "t3=", "num-temps="]) |
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except getopt.GetoptError as err: |
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print(str(err)) |
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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 == "--rp": |
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rp = int(arg) |
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elif opt == "--t1": |
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arg = arg.split(':') |
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t1 = float(arg[0]) |
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r1 = float(arg[1]) |
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elif opt == "--t2": |
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arg = arg.split(':') |
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t2 = float(arg[0]) |
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r2 = float(arg[1]) |
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elif opt == "--t3": |
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arg = arg.split(':') |
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t3 = float(arg[0]) |
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r3 = float(arg[1]) |
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elif opt == "--num-temps": |
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num_temps = int(arg) |
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t = Thermistor(rp, t1, r1, t2, r2, t3, r3) |
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increment = int((ARES - 1) / (num_temps - 1)) |
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step = int((TMIN - TMAX) / (num_temps - 1)) |
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low_bound = t.temp(ARES - 1) |
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up_bound = t.temp(1) |
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min_temp = int(TMIN if TMIN > low_bound else low_bound) |
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max_temp = int(TMAX if TMAX < up_bound else up_bound) |
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temps = list(range(max_temp, TMIN + step, step)) |
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print("// Thermistor lookup table for Marlin") |
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print("// ./createTemperatureLookupMarlin.py --rp=%s --t1=%s:%s --t2=%s:%s --t3=%s:%s --num-temps=%s" % (rp, t1, r1, t2, r2, t3, r3, num_temps)) |
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print("// Steinhart-Hart Coefficients: a=%.15g, b=%.15g, c=%.15g " % (t.c1, t.c2, t.c3)) |
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print("// Theoretical limits of thermistor: %.2f to %.2f degC" % (low_bound, up_bound)) |
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print() |
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print("const short temptable[][2] PROGMEM = {") |
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for temp in temps: |
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adc = t.adc(temp) |
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print(" { OV(%7.2f), %4s }%s // v=%.3f\tr=%.3f\tres=%.3f degC/count" % (adc , temp, \ |
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',' if temp != temps[-1] else ' ', \ |
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t.voltage(adc), \ |
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t.resist( adc), \ |
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t.resol( adc) \ |
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)) |
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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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