1 files changed, 139 insertions, 0 deletions
diff --git a/src/Heating/Sensors/Thermistor.cpp b/src/Heating/Sensors/Thermistor.cpp
new file mode 100644
index 00000000..83e967df
--- /dev/null
+++ b/src/Heating/Sensors/Thermistor.cpp
@@ -0,0 +1,139 @@
+/*
+ * Thermistor.cpp
+ *
+ *  Created on: 10 Nov 2016
+ *      Author: David
+ */
+
+#include "Thermistor.h"
+#include "Platform.h"
+#include "RepRap.h"
+#include "GCodes/GCodeBuffer.h"
+
+// The Steinhart-Hart equation for thermistor resistance is:
+// 1/T = A + B ln(R) + C [ln(R)]^3
+//
+// The simplified (beta) equation assumes C=0 and is:
+// 1/T = A + (1/Beta) ln(R)
+//
+// The parameters that can be configured in RRF are R25 (the resistance at 25C), Beta, and optionally C.
+
+// Create an instance with default values
+Thermistor::Thermistor(unsigned int channel)
+	: TemperatureSensor(channel - FirstThermistorChannel, "Thermistor"), adcLowOffset(0), adcHighOffset(0)
+{
+	r25 = (channel == FirstThermistorChannel) ? BED_R25 : EXT_R25;
+	beta = (channel == FirstThermistorChannel) ? BED_BETA : EXT_BETA;
+	shC = (channel == FirstThermistorChannel) ? BED_SHC : EXT_SHC;
+	seriesR = THERMISTOR_SERIES_RS;
+	CalcDerivedParameters();
+}
+
+void Thermistor::Init()
+{
+	reprap.GetPlatform().GetThermistorFilter(GetSensorChannel() - FirstThermistorChannel).Init((1 << AdcBits) - 1);
+}
+
+// Configure the temperature sensor
+bool Thermistor::Configure(unsigned int mCode, unsigned int heater, GCodeBuffer& gb, StringRef& reply, bool& error)
+{
+	bool seen = false;
+	if (mCode == 305)
+	{
+		// We must set the 25C resistance and beta together in order to calculate Rinf. Check for these first.
+
+		gb.TryGetFValue('T', r25, seen);
+		gb.TryGetFValue('B', beta, seen);
+		gb.TryGetFValue('C', shC, seen);
+		gb.TryGetFValue('R', seriesR, seen);
+		if (seen)
+		{
+			CalcDerivedParameters();
+		}
+
+		if (gb.Seen('L'))
+		{
+			adcLowOffset = (int8_t)constrain<int>(gb.GetIValue(), -100, 100);
+			seen = true;
+		}
+		if (gb.Seen('H'))
+		{
+			adcHighOffset = (int8_t)constrain<int>(gb.GetIValue(), -100, 100);
+			seen = true;
+		}
+
+		TryConfigureHeaterName(gb, seen);
+
+		if (!seen && !gb.Seen('X'))
+		{
+			CopyBasicHeaterDetails(heater, reply);
+			reply.catf(", T:%.1f B:%.1f C:%.2e R:%.1f L:%d H:%d",
+					r25, beta, shC, seriesR, adcLowOffset, adcHighOffset);
+		}
+	}
+
+	return seen;
+}
+
+// Get the temperature
+TemperatureError Thermistor::GetTemperature(float& t)
+{
+	const volatile ThermistorAveragingFilter& filter = reprap.GetPlatform().GetThermistorFilter(GetSensorChannel() - FirstThermistorChannel);
+	if (filter.IsValid())
+	{
+		const int32_t averagedReading = filter.GetSum()/(ThermistorAverageReadings >> Thermistor::AdcOversampleBits);
+		const float temp = CalcTemperature(averagedReading);
+
+		if (temp < MinimumConnectedTemperature)
+		{
+			// thermistor is disconnected
+			t = ABS_ZERO;
+			return TemperatureError::openCircuit;
+		}
+
+		t = temp;
+		return TemperatureError::success;
+	}
+
+	// Filter is not ready yet
+	t = BAD_ERROR_TEMPERATURE;
+	return TemperatureError::busBusy;
+}
+
+// Calculate temperature from an ADC reading in the range 0..1
+float Thermistor::CalcTemperature(int32_t adcReading) const
+{
+	const float denom = (float)(AdcRange  + (int)adcHighOffset - adcReading) - 0.5;
+	if (denom <= 0.0)
+	{
+		return ABS_ZERO;
+	}
+	const float resistance = seriesR * ((float)(adcReading - (int)adcLowOffset) + 0.5)/denom;
+	const float logResistance = log(resistance);
+	const float recipT = shA + shB * logResistance + shC * logResistance * logResistance * logResistance;
+	return (recipT > 0.0) ? (1.0/recipT) + ABS_ZERO : BAD_ERROR_TEMPERATURE;
+}
+
+// Calculate expected ADC reading at a particular temperature, rounded down as the ADC does
+int32_t Thermistor::CalcAdcReading(float temperature) const
+{
+	const double bDFiv3c = shB/(3.0 * shC);
+	const double halfY = (shA - 1.0/(temperature - ABS_ZERO))/(2.0 * shC);
+	const double x = sqrt((bDFiv3c * bDFiv3c * bDFiv3c) + (halfY * halfY));
+	const double oneThird = 1.0/3.0;
+	const float resistance = exp(pow(x - halfY, oneThird) - pow(x + halfY, oneThird));
+	const float fraction = resistance/(resistance + seriesR);
+	const int32_t actualAdcRange = AdcRange  + (int)adcHighOffset - (int)adcLowOffset;
+	const int32_t val = (int32_t)(fraction * (float)actualAdcRange) + (int)adcLowOffset;
+	return constrain<int>(val, 0, AdcRange - 1);
+}
+
+// Calculate shA and shB from the other parameters
+void Thermistor::CalcDerivedParameters()
+{
+	shB = 1.0/beta;
+	const double lnR25 = log(r25);
+	shA = 1.0/(25.0 - ABS_ZERO) - shB * lnR25 - shC * lnR25 * lnR25 * lnR25;
+}
+
+// End