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通过热敏电阻计算温度（三）—Marlin实现分析
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 tableif (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 GeneratorGenerates lookup to temperature values for use in a microcontroller in C format based on:
http://en.wikipedia.org/wiki/Steinhart-Hart_equationThe main use is for Arduino programs that read data from the circuit board described here:
http://reprap.org/wiki/Temperature_Sensor_v2.0Usage: 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 tableclass 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 scaley2 = 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)*l1if c < 0:print "//"print "// WARNING: negative coefficient 'c'! Something may be wrong with the measurements! //"print "//"c = -cself.c1 = a # Steinhart-Hart coefficientsself.c2 = bself.c3 = cself.rp = rp # pull-up resistancedef resol(self, adc):"Convert ADC reading into a resolution"res = self.temp(adc)-self.temp(adc+1)return resdef voltage(self, adc):"Convert ADC reading into a Voltage"return adc * VSTEP # convert the 10 bit ADC value to a voltagedef resist(self, adc):"Convert ADC reading into a resistance in Ohms"r = self.rp * self.voltage(adc) / (VCC - self.voltage(adc)) # resistance of thermistorreturn rdef 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 temperaturereturn (1/Tinv) - ZERO # temperaturedef 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)) * ARESdef 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 tabletry: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)printprint "#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:])
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