Commit thermistor.c, should have been added in f35ccb540b

firmware/src/thermistor.c

@@ -0,0 +1,81 @@
+/*
+ * Thermistor equations
+ * Copyright (C) 2015 Adam Cately, Richard Meadows
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <math.h>
+
+#define SERIES_RESISTOR 100000
+#define ADC_MAX_VALUE (1.85)
+
+/**
+ * Calculate the temperature corresponding to the voltage read from the potential divider.
+ * Note: Uses full Steinhart–Hart equation
+ * Parameters: volatge = raw ADC value from 0 - ADC_MAX_VALUE
+ */
+float thermistor_voltage_to_temperature(float voltage)
+{
+  float resistance;
+
+  /* Coefficients precomputed (can also use http://www.rusefi.com/Steinhart-Hart.html ) */
+  float A = 0.0011293919788944533;
+  float B = 0.00023410122017736258;
+  float C = 0.00000008763737806081768;
+
+  /* convert the value to resistance */
+  resistance = (SERIES_RESISTOR * ADC_MAX_VALUE) / voltage;
+  resistance -= SERIES_RESISTOR;
+
+  float logR = log(resistance);
+  float temperature = A + B*logR + C*pow(logR, 3);
+  temperature = 1.0 / temperature;
+
+  return (float)temperature - 273.15;
+}
+
+/* void CalculateSteinhartCoefficients(){ */
+/*   //Reference temperatures and corresponding resistances to tune algorithm */
+/*   float sampleTemperatures[] = {-55.0, -15.0, 25.0}; */
+/*   float sampleResistances[] = {963000, 72930, 10000}; */
+
+/*   float L1 = log(sampleResistances[0]); */
+/*   float L2 = log(sampleResistances[1]); */
+/*   float L3 = log(sampleResistances[2]); */
+
+/*   float Y1 = 1.0 / (sampleTemperatures[0] + 273.15); */
+/*   float Y2 = 1.0 / (sampleTemperatures[1] + 273.15); */
+/*   float Y3 = 1.0 / (sampleTemperatures[2] + 273.15); */
+
+/*   float G2 = (Y2 - Y1) / (L2 - L1); */
+/*   float G3 = (Y3 - Y1) / (L3 - L1); */
+
+/*   float C = (G3 - G2) / (L3 - L2); */
+/*   C /= (L1 + L2 + L3); */
+
+/*   float B = G2; */
+/*   B -= C*( (L1 * L1) + (L1 * L2) + (L2 * L2) ); */
+
+/*   float A = Y1 - ( B + (L1*L1)*C )*L1; */
+
+/*   printf("A: %g, B: %g, C: %g\n", A, B, C); */
+/* } */