added temperature and altitude estimation from atmospheric pressure

ESP32/src/DataLogger.cpp

@@ -51,7 +51,7 @@ void DataLogger::open()
 	file = SPIFFS.open(fileName, FILE_WRITE);
 	if(!isOpen()) Serial.println("DataLogger: failed to open file");
 
-	if(!file.print("time,speed,battery voltage,battery output current\n")) Serial.println("DataLogger: failed to write to file");
+	if(!file.print("time,speed,battery voltage,battery output current,temperature,altitude\n")) Serial.println("DataLogger: failed to write to file");
 }
 
 void DataLogger::close()
@@ -69,7 +69,7 @@ void DataLogger::log(unsigned long timeMilliseconds, const Entry& entry)
 	if((lastEntry.isDifferent(entry) || currentTime >= lastLogTime + 20.0f) && currentTime >= lastLogTime + 0.2f)
 	{
 		char line[128];
-		sprintf(line, "%.3f,%.3f,%.3f,%.3f\n", currentTime, entry.speed, entry.batteryVoltage, entry.batteryOutputCurrent);
+		sprintf(line, "%.3f,%.3f,%.3f,%.3f,%.1f,%.1f\n", currentTime, entry.speed, entry.batteryVoltage, entry.batteryOutputCurrent, entry.temperature, entry.altitude);
 		file.print(line);
 
 		lastEntry = entry;

ESP32/src/DataLogger.h

@@ -9,6 +9,8 @@ public:
 		float batteryVoltage = 0.0f; // V
 		float batteryOutputCurrent = 0.0f; // A
 		float speed = 0.0f; // m/s
+		float temperature = 0.0f; // in °C
+		float altitude = 0.0f; // in m
 
 		bool isDifferent(const Entry& other)
 		{
@@ -16,7 +18,9 @@ public:
 			return
 				   std::abs(batteryVoltage - other.batteryVoltage) > 0.1f * scale
 				|| std::abs(batteryOutputCurrent - other.batteryOutputCurrent) > 0.1f * scale
-				|| std::abs(speed - other.speed) > 0.1f;
+				|| std::abs(speed - other.speed) > 0.1f
+				|| std::abs(temperature - other.temperature) > 0.5f * scale
+				|| std::abs(altitude - other.altitude) > 0.5f * scale;
 		}
 	};
 

ESP32/src/vehicle-monitor.cpp

@@ -6,6 +6,8 @@
 #include <SPIFFS.h>
 #include <ESPAsyncWebServer.h>
 
+#include <Dps310.h>
+
 #include "ADC.h"
 #include "OTA.h"
 #include "DataLogger.h"
@@ -13,14 +15,19 @@
 
 #include "wifi-credentials.h"
 
+#include <limits>
+
 #define DUMMY_DATA 0
 
 AsyncWebServer server(80);
 
 ADC currentSensor(36);
 ADC batterySensor(39);
+Dps310 pressureSensor = Dps310();
 const int8_t speedSensorPin = 13;
 const int8_t debugLedPin = 2;
+const int8_t I2C_SDA = 12;
+const int8_t I2C_SCL = 15;
 
 const float wheelDiameterInches = 20;
 const int numImpulsesPerTurn = 2;
@@ -28,6 +35,8 @@ const float wheelCircumferenceMeters = wheelDiameterInches * 0.0254f * 3.1415f /
 
 uint16_t batteryVoltage = 0; // in mV
 uint16_t batteryOutputCurrent = 0; // in mV
+int16_t temperature = 0; // in tenth of °C
+int32_t altitude = 0; // in mm above sea level (can be negative if below sea level, or depending on atmospheric conditions)
 
 WiFiMulti wifiMulti;
 wl_status_t wifi_STA_status = WL_NO_SHIELD;
@@ -163,10 +172,16 @@ void setup()
 	
 	OTA.begin();
 
+	Wire.begin(I2C_SDA, I2C_SCL);
+
+	pressureSensor.begin(Wire);
+
 	server.on("/api/status", HTTP_GET, [](AsyncWebServerRequest *request){
 		int v = batteryVoltage;
 		int c = batteryOutputCurrent;
 		int s = (int)(getSpeed() * 1000.0f + 0.5f);
+		int t = temperature;
+		int alt = altitude;
 
 		const char* logFileName = DataLogger::get().currentLogFileName();
 		if(String(logFileName).startsWith("/log/")) logFileName += 5;
@@ -175,7 +190,7 @@ void setup()
 		int usedSize = (int)(SPIFFS.usedBytes() / 1000);
 
 		char json[128];
-		sprintf(json, "{\"v\":%d,\"c\":%d,\"s\":%d,\"log\":\"%s\",\"tot\":%d,\"used\":%d}", v, c, s, logFileName, totalSize, usedSize);
+		sprintf(json, "{\"v\":%d,\"c\":%d,\"s\":%d,\"t\":%d,\"alt\":%d,\"log\":\"%s\",\"tot\":%d,\"used\":%d}", v, c, s, t, alt, logFileName, totalSize, usedSize);
 		request->send(200, "text/json", json);
 	});
 
@@ -295,11 +310,73 @@ void handle_ADC_measures()
 	#endif
 }
 
+void handle_pressure_measure()
+{
+	const uint8_t oversampling = 7;
+	int16_t ret;
+
+	float temp; // in Celcius degrees
+	ret = pressureSensor.measureTempOnce(temp, oversampling);
+	if(ret != 0)
+	{
+		Serial.print("Failed to measure temperature: "); Serial.println(ret);
+		return;
+	}
+	temperature = (int16_t)(temp * 10.0f + 0.5f);
+
+	float pressure; // in Pa
+	pressureSensor.measurePressureOnce(pressure, oversampling);
+	if(ret != 0)
+	{
+		Serial.print("Failed to measure pressure: "); Serial.println(ret);
+		return;
+	}
+
+	struct PressureToAltitude
+	{
+		float pressure; // in Pa
+		float altitude; // in meters above sea level
+	};
+	const PressureToAltitude altitudeTable[] =
+	{
+		{ 101325.0f, 0.0f },
+		{ 100000.0f, 111.0f },
+		{ 95000.0f, 540.0f },
+		{ 90000.0f, 989.0f },
+		{ 85000.0f, 1457.0f },
+		{ 80000.0f, 1949.0f },
+		{ 75000.0f, 2466.0f },
+		{ 70000.0f, 3012.0f },
+		{ 65000.0f, 3591.0f },
+		{ 60000.0f, 4206.0f },
+		{ 55000.0f, 4865.0f },
+	};
+	const int8_t altitudeTableNumValues = sizeof(altitudeTable)/sizeof(altitudeTable[0]);
+
+	float alt = -std::numeric_limits<float>::max();
+	for(int8_t i = 0; i < altitudeTableNumValues - 1; ++i)
+	{
+		if(i == altitudeTableNumValues - 2 || pressure >= altitudeTable[i+1].pressure)
+		{
+			const auto& p = altitudeTable[i];
+			const auto& n = altitudeTable[i+1];
+			alt = (pressure - p.pressure) / (n.pressure - p.pressure) * (n.altitude - p.altitude) + p.altitude;
+			break;
+		}
+	}
+	altitude = (int32_t)(alt * 1000.0f + 0.5f);
+
+	/*Serial.print("temperature="); Serial.print(temp); Serial.print("°C");
+	Serial.print("  pressure="); Serial.print(pressure); Serial.print("Pa");
+	Serial.print("  altitude="); Serial.print(altitude); Serial.println("mm");*/
+}
+
 void loop()
 {
 	OTA.handle();
 	handle_wifi_connection();
 	handle_ADC_measures();
+	handle_pressure_measure(); // also measures temperature
 
 	unsigned long now = millis();
 	static DataLogger::Entry entry;
@@ -333,5 +410,5 @@ void loop()
 	}
 	DataLogger::get().log(now, entry);
 
-	delay(10);
+	delay(DataLogger::get().isOpen() ? 10 : 1000);
 }