You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
157 lines
6.1 KiB
Python
157 lines
6.1 KiB
Python
#!/usr/bin/python
|
|
"""Thermistor Value Lookup Table Generator
|
|
|
|
Generates lookup to temperature values for use in a microcontroller in C format based on:
|
|
http://en.wikipedia.org/wiki/Steinhart-Hart_equation
|
|
|
|
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
|
|
--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 math import *
|
|
import sys
|
|
import getopt
|
|
|
|
"Constants"
|
|
ZERO = 273.15 # zero point of Kelvin scale
|
|
VADC = 5 # ADC voltage
|
|
VCC = 5 # supply voltage
|
|
ARES = 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 = 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 termistor: %.2f to %.2f degC" % (low_bound, up_bound)
|
|
print
|
|
print "#define NUMTEMPS %s" % (len(temps))
|
|
print "const short temptable[NUMTEMPS][2] PROGMEM = {"
|
|
|
|
for temp in temps:
|
|
adc = t.adc(temp)
|
|
print " { (short) (%7.2f * OVERSAMPLENR ), %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:])
|