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authorGeorgiy Bondarenko <69736697+nehilo@users.noreply.github.com>2021-03-04 20:54:23 +0300
committerGeorgiy Bondarenko <69736697+nehilo@users.noreply.github.com>2021-03-04 20:54:23 +0300
commite8701195e66f2d27ffe17fb514eae8173795aaf7 (patch)
tree9f519c4abf6556b9ae7190a6210d87ead1dfadde /buildroot/share/scripts/createTemperatureLookupMarlin.py
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+#!/usr/bin/env python
+"""Thermistor Value Lookup Table Generator
+
+Generates lookup to temperature values for use in a microcontroller in C format based on:
+https://en.wikipedia.org/wiki/Steinhart-Hart_equation
+
+The main use is for Arduino programs that read data from the circuit board described here:
+https://reprap.org/wiki/Temperature_Sensor_v2.0
+
+Usage: python createTemperatureLookupMarlin.py [options]
+
+Options:
+ -h, --help show this help
+ --rp=... pull-up resistor
+ --t1=ttt:rrr low temperature temperature:resistance point (around 25 degC)
+ --t2=ttt:rrr middle temperature temperature:resistance point (around 150 degC)
+ --t3=ttt:rrr high temperature temperature:resistance point (around 250 degC)
+ --num-temps=... the number of temperature points to calculate (default: 36)
+"""
+
+from __future__ import print_function
+from __future__ import division
+
+from math import *
+import sys
+import getopt
+
+"Constants"
+ZERO = 273.15 # zero point of Kelvin scale
+VADC = 5 # ADC voltage
+VCC = 5 # supply voltage
+ARES = pow(2,10) # 10 Bit ADC resolution
+VSTEP = VADC / ARES # ADC voltage resolution
+TMIN = 0 # lowest temperature in table
+TMAX = 350 # highest temperature in table
+
+class Thermistor:
+ "Class to do the thermistor maths"
+ def __init__(self, rp, t1, r1, t2, r2, t3, r3):
+ l1 = log(r1)
+ l2 = log(r2)
+ l3 = log(r3)
+ y1 = 1.0 / (t1 + ZERO) # adjust scale
+ y2 = 1.0 / (t2 + ZERO)
+ y3 = 1.0 / (t3 + ZERO)
+ x = (y2 - y1) / (l2 - l1)
+ y = (y3 - y1) / (l3 - l1)
+ c = (y - x) / ((l3 - l2) * (l1 + l2 + l3))
+ b = x - c * (l1**2 + l2**2 + l1*l2)
+ a = y1 - (b + l1**2 *c)*l1
+
+ if c < 0:
+ print("//////////////////////////////////////////////////////////////////////////////////////")
+ print("// WARNING: negative coefficient 'c'! Something may be wrong with the measurements! //")
+ print("//////////////////////////////////////////////////////////////////////////////////////")
+ c = -c
+ self.c1 = a # Steinhart-Hart coefficients
+ self.c2 = b
+ self.c3 = c
+ self.rp = rp # pull-up resistance
+
+ def resol(self, adc):
+ "Convert ADC reading into a resolution"
+ res = self.temp(adc)-self.temp(adc+1)
+ return res
+
+ def voltage(self, adc):
+ "Convert ADC reading into a Voltage"
+ return adc * VSTEP # convert the 10 bit ADC value to a voltage
+
+ def resist(self, adc):
+ "Convert ADC reading into a resistance in Ohms"
+ r = self.rp * self.voltage(adc) / (VCC - self.voltage(adc)) # resistance of thermistor
+ return r
+
+ def temp(self, adc):
+ "Convert ADC reading into a temperature in Celcius"
+ l = log(self.resist(adc))
+ Tinv = self.c1 + self.c2*l + self.c3* l**3 # inverse temperature
+ return (1/Tinv) - ZERO # temperature
+
+ def adc(self, temp):
+ "Convert temperature into a ADC reading"
+ x = (self.c1 - (1.0 / (temp+ZERO))) / (2*self.c3)
+ y = sqrt((self.c2 / (3*self.c3))**3 + x**2)
+ r = exp((y-x)**(1.0/3) - (y+x)**(1.0/3))
+ return (r / (self.rp + r)) * ARES
+
+def main(argv):
+ "Default values"
+ t1 = 25 # low temperature in Kelvin (25 degC)
+ r1 = 100000 # resistance at low temperature (10 kOhm)
+ t2 = 150 # middle temperature in Kelvin (150 degC)
+ r2 = 1641.9 # resistance at middle temperature (1.6 KOhm)
+ t3 = 250 # high temperature in Kelvin (250 degC)
+ r3 = 226.15 # resistance at high temperature (226.15 Ohm)
+ rp = 4700; # pull-up resistor (4.7 kOhm)
+ num_temps = 36; # number of entries for look-up table
+
+ try:
+ opts, args = getopt.getopt(argv, "h", ["help", "rp=", "t1=", "t2=", "t3=", "num-temps="])
+ except getopt.GetoptError as err:
+ print(str(err))
+ usage()
+ sys.exit(2)
+
+ for opt, arg in opts:
+ if opt in ("-h", "--help"):
+ usage()
+ sys.exit()
+ elif opt == "--rp":
+ rp = int(arg)
+ elif opt == "--t1":
+ arg = arg.split(':')
+ t1 = float(arg[0])
+ r1 = float(arg[1])
+ elif opt == "--t2":
+ arg = arg.split(':')
+ t2 = float(arg[0])
+ r2 = float(arg[1])
+ elif opt == "--t3":
+ arg = arg.split(':')
+ t3 = float(arg[0])
+ r3 = float(arg[1])
+ elif opt == "--num-temps":
+ num_temps = int(arg)
+
+ t = Thermistor(rp, t1, r1, t2, r2, t3, r3)
+ increment = int((ARES-1)/(num_temps-1));
+ step = (TMIN-TMAX) / (num_temps-1)
+ low_bound = t.temp(ARES-1);
+ up_bound = t.temp(1);
+ min_temp = int(TMIN if TMIN > low_bound else low_bound)
+ max_temp = int(TMAX if TMAX < up_bound else up_bound)
+ temps = list(range(max_temp, TMIN+step, step));
+
+ print("// Thermistor lookup table for Marlin")
+ 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))
+ print("// Steinhart-Hart Coefficients: a=%.15g, b=%.15g, c=%.15g " % (t.c1, t.c2, t.c3))
+ print("// Theoretical limits of thermistor: %.2f to %.2f degC" % (low_bound, up_bound))
+ print()
+ print("const short temptable[][2] PROGMEM = {")
+
+ for temp in temps:
+ adc = t.adc(temp)
+ print(" { OV(%7.2f), %4s }%s // v=%.3f\tr=%.3f\tres=%.3f degC/count" % (adc , temp, \
+ ',' if temp != temps[-1] else ' ', \
+ t.voltage(adc), \
+ t.resist( adc), \
+ t.resol( adc) \
+ ))
+ print("};")
+
+def usage():
+ print(__doc__)
+
+if __name__ == "__main__":
+ main(sys.argv[1:])