Initial commit

Author: domoticsduino

README.md

@@ -1,2 +1,2 @@
-# smarthome-fw-lib-esp8266-ddmq4
-Library to interface MQ-4 gas sensor
+# Smarthome firmware library for ESP8266 - MQ-4 gas sensor
+Library with functions for MQ-4 gas sensor based on ESP8266 board

ddmq4.cpp

@@ -0,0 +1,125 @@
+/* 1.0.0 VERSION */
+
+#include "ddmq4.h"
+
+DDMQ4::DDMQ4(int pin)
+{
+	this->_analogPin = pin;
+}
+
+DDMQ4Val DDMQ4::getValue()
+{
+
+	float sensor_volt; //Define variable for sensor voltage
+	float RS_gas;			 //Define variable for sensor resistance
+	float ratio;			 //Define variable for ratio
+
+	float sensorValue = analogRead(this->_analogPin);
+
+	sensor_volt = sensorValue * (3.3 / 1023.0);		//Convert analog values to voltage
+	RS_gas = ((3.3 * 10.0) / sensor_volt) - 10.0; //Get value of RS in a gas
+	ratio = RS_gas / this->_R0;										// Get ratio RS_gas/RS_air
+
+	double ppm_log = (log10(ratio) - this->_b) / this->_m; //Get ppm value in linear scale according to the the ratio value
+	double ppm = pow(10, ppm_log);												 //Convert ppm value to log scale
+	double percentage = ppm / 10000;											 //Convert to percentage
+
+	float realValue = 0.0;
+
+	if (sensorValue > this->_valorecentrale)
+	{
+		realValue = this->fscale(this->_valorecentrale, 1023, 1000, 10000, sensorValue, 10);
+	}
+	else
+	{
+		realValue = this->fscale(0, this->_valorecentrale, 200, 1000, sensorValue, 10);
+	}
+
+	DDMQ4Val ret;
+	ret.realValue = realValue;
+	ret.ppm = ppm;
+	ret.sensorValue = sensorValue;
+	ret.percentage = percentage;
+	ret.success = true;
+
+	return ret;
+}
+
+float DDMQ4::fscale(float originalMin, float originalMax, float newBegin, float newEnd, float inputValue, float curve)
+{
+
+	float OriginalRange = 0;
+	float NewRange = 0;
+	float zeroRefCurVal = 0;
+	float normalizedCurVal = 0;
+	float rangedValue = 0;
+	boolean invFlag = 0;
+
+	// condition curve parameter
+	// limit range
+
+	if (curve > 10)
+		curve = 10;
+	if (curve < -10)
+		curve = -10;
+
+	curve = (curve * -.1);	// - invert and scale - this seems more intuitive - postive numbers give more weight to high end on output
+	curve = pow(10, curve); // convert linear scale into lograthimic exponent for other pow function
+
+	/*
+    Serial.println(curve * 100, DEC);   // multply by 100 to preserve resolution  
+    Serial.println(); 
+    */
+
+	// Check for out of range inputValues
+	if (inputValue < originalMin)
+	{
+		inputValue = originalMin;
+	}
+	if (inputValue > originalMax)
+	{
+		inputValue = originalMax;
+	}
+
+	// Zero Refference the values
+	OriginalRange = originalMax - originalMin;
+
+	if (newEnd > newBegin)
+	{
+		NewRange = newEnd - newBegin;
+	}
+	else
+	{
+		NewRange = newBegin - newEnd;
+		invFlag = 1;
+	}
+
+	zeroRefCurVal = inputValue - originalMin;
+	normalizedCurVal = zeroRefCurVal / OriginalRange; // normalize to 0 - 1 float
+
+	/*
+    Serial.print(OriginalRange, DEC);  
+    Serial.print("   ");  
+    Serial.print(NewRange, DEC);  
+    Serial.print("   ");  
+    Serial.println(zeroRefCurVal, DEC);  
+    Serial.println();  
+    */
+
+	// Check for originalMin > originalMax  - the math for all other cases i.e. negative numbers seems to work out fine
+	if (originalMin > originalMax)
+	{
+		return 0;
+	}
+
+	if (invFlag == 0)
+	{
+		rangedValue = (pow(normalizedCurVal, curve) * NewRange) + newBegin;
+	}
+	else // invert the ranges
+	{
+		rangedValue = newBegin - (pow(normalizedCurVal, curve) * NewRange);
+	}
+
+	return rangedValue;
+}

ddmq4.h

@@ -0,0 +1,38 @@
+/* 1.0.0 VERSION */
+
+#ifndef ddmq4_h
+#define ddmq4_h
+
+#include <Arduino.h>
+
+struct DDMQ4Val {
+
+    float sensorValue = 0.0;
+    double ppm = 0.0;
+    double percentage = 0.0;
+    float realValue = 0.0;
+    bool success = false;
+    const char* errorMsg;
+
+};
+
+class DDMQ4 {
+    
+    private:
+        int _analogPin;
+        float _m = -0.318; //Slope
+        float _b = 1.133; //Y-Intercept
+        float _R0 = 11.820; //Sensor Resistance in fresh air from previous code
+        float _valorecentrale = 512.0; //valore che corrisponde a 1000ppm - da ricavare in base allo schema elettrico
+
+        float fscale(float, float, float, float, float, float);
+
+    public:
+
+        DDMQ4(int);
+        
+        DDMQ4Val getValue();
+
+};
+
+#endif