My Marlin configs for Fabrikator Mini and CTC i3 Pro B
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createTemperatureLookupMarlin.py 6.1KB

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  1. #!/usr/bin/python
  2. """Thermistor Value Lookup Table Generator
  3. Generates lookup to temperature values for use in a microcontroller in C format based on:
  4. http://en.wikipedia.org/wiki/Steinhart-Hart_equation
  5. The main use is for Arduino programs that read data from the circuit board described here:
  6. http://make.rrrf.org/ts-1.0
  7. Usage: python createTemperatureLookup.py [options]
  8. Options:
  9. -h, --help show this help
  10. --rp=... pull-up resistor
  11. --t1=ttt:rrr low temperature temperature:resistance point (around 25 degC)
  12. --t2=ttt:rrr middle temperature temperature:resistance point (around 150 degC)
  13. --t3=ttt:rrr high temperature temperature:resistance point (around 250 degC)
  14. --num-temps=... the number of temperature points to calculate (default: 36)
  15. """
  16. from math import *
  17. import sys
  18. import getopt
  19. "Constants"
  20. ZERO = 273.15 # zero point of Kelvin scale
  21. VADC = 5 # ADC voltage
  22. VCC = 5 # supply voltage
  23. ARES = pow(2,10) # 10 Bit ADC resolution
  24. VSTEP = VADC / ARES # ADC voltage resolution
  25. TMIN = 0 # lowest temperature in table
  26. TMAX = 350 # highest temperature in table
  27. class Thermistor:
  28. "Class to do the thermistor maths"
  29. def __init__(self, rp, t1, r1, t2, r2, t3, r3):
  30. l1 = log(r1)
  31. l2 = log(r2)
  32. l3 = log(r3)
  33. y1 = 1.0 / (t1 + ZERO) # adjust scale
  34. y2 = 1.0 / (t2 + ZERO)
  35. y3 = 1.0 / (t3 + ZERO)
  36. x = (y2 - y1) / (l2 - l1)
  37. y = (y3 - y1) / (l3 - l1)
  38. c = (y - x) / ((l3 - l2) * (l1 + l2 + l3))
  39. b = x - c * (l1**2 + l2**2 + l1*l2)
  40. a = y1 - (b + l1**2 *c)*l1
  41. if c < 0:
  42. print "//////////////////////////////////////////////////////////////////////////////////////"
  43. print "// WARNING: negative coefficient 'c'! Something may be wrong with the measurements! //"
  44. print "//////////////////////////////////////////////////////////////////////////////////////"
  45. c = -c
  46. self.c1 = a # Steinhart-Hart coefficients
  47. self.c2 = b
  48. self.c3 = c
  49. self.rp = rp # pull-up resistance
  50. def resol(self, adc):
  51. "Convert ADC reading into a resolution"
  52. res = self.temp(adc)-self.temp(adc+1)
  53. return res
  54. def voltage(self, adc):
  55. "Convert ADC reading into a Voltage"
  56. return adc * VSTEP # convert the 10 bit ADC value to a voltage
  57. def resist(self, adc):
  58. "Convert ADC reading into a resistance in Ohms"
  59. r = self.rp * self.voltage(adc) / (VCC - self.voltage(adc)) # resistance of thermistor
  60. return r
  61. def temp(self, adc):
  62. "Convert ADC reading into a temperature in Celcius"
  63. l = log(self.resist(adc))
  64. Tinv = self.c1 + self.c2*l + self.c3* l**3 # inverse temperature
  65. return (1/Tinv) - ZERO # temperature
  66. def adc(self, temp):
  67. "Convert temperature into a ADC reading"
  68. x = (self.c1 - (1.0 / (temp+ZERO))) / (2*self.c3)
  69. y = sqrt((self.c2 / (3*self.c3))**3 + x**2)
  70. r = exp((y-x)**(1.0/3) - (y+x)**(1.0/3))
  71. return (r / (self.rp + r)) * ARES
  72. def main(argv):
  73. "Default values"
  74. t1 = 25 # low temperature in Kelvin (25 degC)
  75. r1 = 100000 # resistance at low temperature (10 kOhm)
  76. t2 = 150 # middle temperature in Kelvin (150 degC)
  77. r2 = 1641.9 # resistance at middle temperature (1.6 KOhm)
  78. t3 = 250 # high temperature in Kelvin (250 degC)
  79. r3 = 226.15 # resistance at high temperature (226.15 Ohm)
  80. rp = 4700; # pull-up resistor (4.7 kOhm)
  81. num_temps = 36; # number of entries for look-up table
  82. try:
  83. opts, args = getopt.getopt(argv, "h", ["help", "rp=", "t1=", "t2=", "t3=", "num-temps="])
  84. except getopt.GetoptError as err:
  85. print str(err)
  86. usage()
  87. sys.exit(2)
  88. for opt, arg in opts:
  89. if opt in ("-h", "--help"):
  90. usage()
  91. sys.exit()
  92. elif opt == "--rp":
  93. rp = int(arg)
  94. elif opt == "--t1":
  95. arg = arg.split(':')
  96. t1 = float(arg[0])
  97. r1 = float(arg[1])
  98. elif opt == "--t2":
  99. arg = arg.split(':')
  100. t2 = float(arg[0])
  101. r2 = float(arg[1])
  102. elif opt == "--t3":
  103. arg = arg.split(':')
  104. t3 = float(arg[0])
  105. r3 = float(arg[1])
  106. elif opt == "--num-temps":
  107. num_temps = int(arg)
  108. t = Thermistor(rp, t1, r1, t2, r2, t3, r3)
  109. increment = int((ARES-1)/(num_temps-1));
  110. step = (TMIN-TMAX) / (num_temps-1)
  111. low_bound = t.temp(ARES-1);
  112. up_bound = t.temp(1);
  113. min_temp = int(TMIN if TMIN > low_bound else low_bound)
  114. max_temp = int(TMAX if TMAX < up_bound else up_bound)
  115. temps = range(max_temp, TMIN+step, step);
  116. print "// Thermistor lookup table for Marlin"
  117. 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)
  118. print "// Steinhart-Hart Coefficients: a=%.15g, b=%.15g, c=%.15g " % (t.c1, t.c2, t.c3)
  119. print "// Theoretical limits of termistor: %.2f to %.2f degC" % (low_bound, up_bound)
  120. print
  121. print "#define NUMTEMPS %s" % (len(temps))
  122. print "const short temptable[NUMTEMPS][2] PROGMEM = {"
  123. for temp in temps:
  124. adc = t.adc(temp)
  125. print " { (short) (%7.2f * OVERSAMPLENR ), %4s }%s // v=%.3f\tr=%.3f\tres=%.3f degC/count" % (adc , temp, \
  126. ',' if temp != temps[-1] else ' ', \
  127. t.voltage(adc), \
  128. t.resist( adc), \
  129. t.resol( adc) \
  130. )
  131. print "};"
  132. def usage():
  133. print __doc__
  134. if __name__ == "__main__":
  135. main(sys.argv[1:])