marlin固件温度的计算方法采用的是Steinhart-Hart方程计算的方式。首先通过python生成温度查表数据，单片机端可以直接使用查表的方式计算温度数据。
温度查表数据：
OVERSAMPLENR 的值为16，数组中的第一个值为ADC采样值的16倍。因为实际计算中的ADC值是采样16次的和
//专为stm32生成的温度查表
//在此有一点需要注意，这里的数值类型不能再用short类型了，若还用short类型会报一系列警告信息，
//同时要注意修改analog2temp(int raw, uint8_t e)函数，将与温度查表相关的类型short改为int类型
const int temptable_1[][2] = {
{ (91 * OVERSAMPLENR ), 300 },
{ (98 * OVERSAMPLENR ), 295 },
{ (105 * OVERSAMPLENR ), 290 },
{ (112 * OVERSAMPLENR ), 285 },
{ (120 * OVERSAMPLENR ), 280 },
{ (129 * OVERSAMPLENR ), 275 },
{ (139 * OVERSAMPLENR ), 270 },
{ (150 * OVERSAMPLENR ), 265 },
{ (161 * OVERSAMPLENR ), 260 },
{ (174 * OVERSAMPLENR ), 255 },
{ (188 * OVERSAMPLENR ), 250 },
{ (203 * OVERSAMPLENR ), 245 },
{ (220 * OVERSAMPLENR ), 240 },
{ (239 * OVERSAMPLENR ), 235 },
{ (259 * OVERSAMPLENR ), 230 },
{ (281 * OVERSAMPLENR ), 225 },
{ (306 * OVERSAMPLENR ), 220 },
{ (332 * OVERSAMPLENR ), 215 },
{ (362 * OVERSAMPLENR ), 210 },
{ (395 * OVERSAMPLENR ), 205 },
{ (431 * OVERSAMPLENR ), 200 },
{ (471 * OVERSAMPLENR ), 195 },
{ (515 * OVERSAMPLENR ), 190 },
{ (563 * OVERSAMPLENR ), 185 },
{ (616 * OVERSAMPLENR ), 180 },
{ (674 * OVERSAMPLENR ), 175 },
{ (739 * OVERSAMPLENR ), 170 },
{ (809 * OVERSAMPLENR ), 165 },
{ (886 * OVERSAMPLENR ), 160 },
{ (969 * OVERSAMPLENR ), 155 },
{ (1060 * OVERSAMPLENR ), 150 },
{ (1159 * OVERSAMPLENR ), 145 },
{ (1265 * OVERSAMPLENR ), 140 },
{ (1379 * OVERSAMPLENR ), 135 },
{ (1501 * OVERSAMPLENR ), 130 },
{ (1630 * OVERSAMPLENR ), 125 },
{ (1765 * OVERSAMPLENR ), 120 },
{ (1906 * OVERSAMPLENR ), 115 },
{ (2052 * OVERSAMPLENR ), 110 },
{ (2202 * OVERSAMPLENR ), 105 },
{ (2353 * OVERSAMPLENR ), 100 },
{ (2504 * OVERSAMPLENR ), 95 },
{ (2654 * OVERSAMPLENR ), 90 },
{ (2800 * OVERSAMPLENR ), 85 },
{ (2942 * OVERSAMPLENR ), 80 },
{ (3076 * OVERSAMPLENR ), 75 },
{ (3203 * OVERSAMPLENR ), 70 },
{ (3321 * OVERSAMPLENR ), 65 },
{ (3429 * OVERSAMPLENR ), 60 },
{ (3527 * OVERSAMPLENR ), 55 },
{ (3615 * OVERSAMPLENR ), 50 },
{ (3692 * OVERSAMPLENR ), 45 },
{ (3760 * OVERSAMPLENR ), 40 },
{ (3819 * OVERSAMPLENR ), 35 },
{ (3869 * OVERSAMPLENR ), 30 },
{ (3912 * OVERSAMPLENR ), 25 },
{ (3948 * OVERSAMPLENR ), 20 },
{ (3978 * OVERSAMPLENR ), 15 },
{ (4002 * OVERSAMPLENR ), 10 },
{ (4022 * OVERSAMPLENR ), 5 },
{ (4039 * OVERSAMPLENR ), 0 },
};
根据温度查表数据将ADC采样值转换为温度数据的函数
// Derived from RepRap FiveD extruder::getTemperature()
// For hot end temperature measurement.//热端温度测量
static float analog2temp(int raw, uint8_t e) { //将温度的adc值转换为对应的温度值
uint8_t i;
if(e >= EXTRUDERS) {
SERIAL_ERROR_START;
printf("%d",e);
printf(" - Invalid extruder number !");
printf("\n");
kill();
}
if(heater_ttbl_map[e] != NULL) {
float celsius = 0;
int (*tt)[][2] = (int (*)[][2])(heater_ttbl_map[e]);
for ( i=1; i<heater_ttbllen_map[e]; i++) { //通过查表利用内差的方式估计挤出头目前的温度
if ((*tt)[i][0] > raw) {
celsius = (*tt)[i-1][1] +
(raw - (*tt)[i-1][0]) *
(float)((*tt)[i][1] - (*tt)[i-1][1]) /
(float)((*tt)[i][0] - (*tt)[i-1][0]);
break;
}
}
// Overflow: Set to last value in the table
if (i == heater_ttbllen_map[e]) celsius = (*tt)[i-1][1];
return celsius; //热敏电阻测量的数据生成的温度值
}
return 0;
//return ((raw * ((5.0 * 100.0) / 1024.0) / OVERSAMPLENR) * TEMP_SENSOR_AD595_GAIN) + TEMP_SENSOR_AD595_OFFSET; //热电偶测得的数据计算温度值
}
生成温度查表数据的python程序
#!/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://reprap.org/wiki/Temperature_Sensor_v2.0
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 = 3.3 # ADC voltage
VCC = 3.3 # supply voltage
ARES = pow(2,12) # 10 Bit ADC resolution
VSTEP = VADC / ARES # ADC voltage resolution
TMIN = 0 # lowest temperature in table
TMAX = 300 # 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 = 61; # 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 long temptable[NUMTEMPS][2] = {"
for temp in temps:
adc = t.adc(temp)
print " { (%d * OVERSAMPLENR ), %4s }%s // v=%s r=%s res=%s degC/count" % ((adc+0.5) , 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:])