implement temp sensor pulldown mode #116

firmware/CHANGELOG.md

@@ -30,6 +30,7 @@ Release template (copy/paste this for new release):
 
 ### Added
  - Log per-cylinder true ignition timing (includes trim, knock retard, etc) #76
+ - Add mode for CLT/IAT sensors that are installed "high side" instead of typical "low side" #116
 
 ### Fixed
  - Improved bench test resolution (more usable for testing injectors, dwell, etc)

firmware/controllers/sensors/converters/resistance_func.cpp

@@ -4,9 +4,10 @@
 
 #include "resistance_func.h"
 
-void ResistanceFunc::configure(float supplyVoltage, float pullupResistor) {
+void ResistanceFunc::configure(float supplyVoltage, float pullupResistor, bool isPulldown) {
 	m_pullupResistor = pullupResistor;
 	m_supplyVoltage = supplyVoltage;
+	m_isPulldown = isPulldown;
 }
 
 SensorResult ResistanceFunc::convert(float raw) const {
@@ -20,6 +21,12 @@ SensorResult ResistanceFunc::convert(float raw) const {
 		return UnexpectedCode::High;
 	}
 
+	if (m_isPulldown) {
+		// If the sensor is on the high side (fixed resistor is pulldown),
+		// invert the voltage so the math comes out correctly
+		raw = m_supplyVoltage - raw;
+	}
+
 	// Voltage is in a sensible range - convert
 	float resistance = m_pullupResistor / (m_supplyVoltage / raw - 1);
 

firmware/controllers/sensors/converters/resistance_func.h

@@ -12,7 +12,7 @@
 
 class ResistanceFunc final : public SensorConverter {
 public:
-	void configure(float supplyVoltage, float pullupResistor);
+	void configure(float supplyVoltage, float pullupResistor, bool isPulldown);
 
 	SensorResult convert(float inputValue) const override;
 
@@ -21,4 +21,5 @@ class ResistanceFunc final : public SensorConverter {
 private:
 	float m_supplyVoltage = 5.0f;
 	float m_pullupResistor = 1000.0f;
+	bool m_isPulldown = false;
 };

firmware/init/sensor/init_thermistors.cpp

@@ -35,15 +35,15 @@ static void validateThermistorConfig(const char *msg, thermistor_conf_s& cfg) {
 }
 
 static SensorConverter& configureTempSensorFunction(const char *msg,
-		thermistor_conf_s& cfg, FuncPair& p, bool isLinear) {
+		thermistor_conf_s& cfg, FuncPair& p, bool isLinear, bool isPulldown) {
 	if (isLinear) {
 		p.linear.configure(cfg.resistance_1, cfg.tempC_1, cfg.resistance_2, cfg.tempC_2, -50, 250);
 
 		return p.linear;
 	} else /* sensor is thermistor */ {
 		validateThermistorConfig(msg, cfg);
 
-		p.thermistor.get<resist>().configure(5.0f, cfg.bias_resistor);
+		p.thermistor.get<resist>().configure(5.0f, cfg.bias_resistor, isPulldown);
 		p.thermistor.get<therm>().configure(cfg);
 
 		return p.thermistor;
@@ -54,29 +54,31 @@ static void configTherm(const char *msg,
 		FunctionalSensor &sensor,
 					FuncPair &p,
 					ThermistorConf &config,
-					bool isLinear) {
+					bool isLinear,
+					bool isPulldown) {
 	// nothing to do if no channel
 	if (!isAdcChannelValid(config.adcChannel)) {
 		return;
 	}
 
 	// Configure the conversion function for this sensor
-	sensor.setFunction(configureTempSensorFunction(msg, config.config, p, isLinear));
+	sensor.setFunction(configureTempSensorFunction(msg, config.config, p, isLinear, isPulldown));
 }
 
 static void configureTempSensor(const char *msg,
 								FunctionalSensor &sensor,
 								FuncPair &p,
 								ThermistorConf &config,
-								bool isLinear) {
+								bool isLinear,
+								bool isPulldown = false) {
 	auto channel = config.adcChannel;
 
 	// Only register if we have a sensor
 	if (!isAdcChannelValid(channel)) {
 		return;
 	}
 
-	configTherm(msg, sensor, p, config, isLinear);
+	configTherm(msg, sensor, p, config, isLinear, isPulldown);
 
 	// Register & subscribe
 	AdcSubscription::SubscribeSensor(sensor, channel, 2);
@@ -88,13 +90,15 @@ void initThermistors() {
 						clt,
 						fclt,
 						engineConfiguration->clt,
-						engineConfiguration->useLinearCltSensor);
+						engineConfiguration->useLinearCltSensor,
+						engineConfiguration->cltSensorPulldown);
 
 	configureTempSensor("iat",
 						iat,
 						fiat,
 						engineConfiguration->iat,
-						engineConfiguration->useLinearIatSensor);
+						engineConfiguration->useLinearIatSensor,
+						engineConfiguration->iatSensorPulldown);
 
 	configureTempSensor("aux1",
 						aux1,

firmware/integration/rusefi_config.txt

@@ -428,7 +428,8 @@ bit usescriptTableForCanSniffingFiltering
 bit verboseCan,"Print all","Do not print";Print incoming and outgoing first bus CAN messages in rusEFI console
 bit artificialTestMisfire,"Danger Mode","No thank you";Experimental setting that will cause a misfire\nDO NOT ENABLE.
 bit useFordRedundantPps;On some Ford and Toyota vehicles one of the pedal sensors is not linear on the full range, i.e. in the specific range of the positions we effectively have only one sensor.
-
+bit cltSensorPulldown
+bit iatSensorPulldown
 
 int16_t tpsMin;Closed throttle, 1 volt = 200 units;"ADC", 1, 0, 0, 1023, 0
 int16_t tpsMax;Full throttle, 1 volt = 200 units;"ADC", 1, 0, 0, 1023, 0

firmware/tunerstudio/rusefi.input

@@ -4256,6 +4256,8 @@ dialog = tcuControls, "Transmission Settings"
 		field = "Ford redundant PPS mode",				useFordRedundantPps
 		field = "Secondary PPS maximum",				ppsSecondaryMaximum, {useFordRedundantPps}
 		field = "ADC vRef voltage",						adcVcc
+		field = "CLT sensor is pulldown instead of pullup", cltSensorPulldown
+		field = "IAT sensor is pulldown instead of pullup", iatSensorPulldown
 		field = "Analog divider ratio",					analogInputDividerCoefficient@@if_ts_show_analog_divider
 		field = "Artificial Misfire",						artificialTestMisfire
 		field = "Instant Rpm Range",                    instantRpmRange

unit_tests/tests/sensor/resist_func.cpp

@@ -9,7 +9,7 @@
 TEST(resistance, OutOfRange)
 {
     ResistanceFunc f;
-    f.configure(5, 10000);
+    f.configure(5, 10000, false);
 
     // Something in the middle should be valid
     {
@@ -45,7 +45,7 @@ TEST(resistance, OutOfRange)
 TEST(resistance, InRange)
 {
     ResistanceFunc f;
-    f.configure(5, 10000);
+    f.configure(5, 10000, false);
 
     // 1 volt -> 2500 ohms low side
     {
@@ -76,3 +76,38 @@ TEST(resistance, InRange)
         EXPECT_FLOAT_EQ(r.Value, 40000);
     }
 }
+
+TEST(resistance, PulldownMode)
+{
+    ResistanceFunc f;
+    f.configure(5, 10000, true);
+
+    // 4 volt -> 2500 ohms high side
+    {
+        auto r = f.convert(4.0f);
+        EXPECT_TRUE(r.Valid);
+        EXPECT_FLOAT_EQ(r.Value, 2500);
+    }
+
+    // 3 volt -> 6666.667 ohm ohms high side
+    // 20k/3 gives us an exact result
+    {
+        auto r = f.convert(3.0f);
+        EXPECT_TRUE(r.Valid);
+        EXPECT_FLOAT_EQ(r.Value, 20000.0f / 3);
+    }
+
+    // 2 volt -> 15000 ohms high side
+    {
+        auto r = f.convert(2.0f);
+        EXPECT_TRUE(r.Valid);
+        EXPECT_FLOAT_EQ(r.Value, 15000);
+    }
+
+    // 1 volt -> 40000 ohms high side
+    {
+        auto r = f.convert(1.0f);
+        EXPECT_TRUE(r.Valid);
+        EXPECT_FLOAT_EQ(r.Value, 40000);
+    }
+}