Added Linear ecuation on test algorithm

examples/AlgorithmTester/AlgorithmTester.ino

@@ -99,6 +99,13 @@ void loop()
     expectedValue[0] = 1000; expectedValue[1] = 3000; expectedValue[2] = 5000; expectedValue[3] = 7000;
     testSensor("MQ-309", 1000000, -4.01);
 
+    // Testing linear equation for MQ-4
+    mySensor.setRegressionMethod(0); //_PPM =  pow(10, (log10(ratio)-b)/a)
+    ratio[0] = 2.5; ratio[1] = 1.5; ratio[2] = 0.9; ratio[3] = 0.65;
+    expectedValue[0] = 200; expectedValue[1] = 1000; expectedValue[2] = 5000; expectedValue[3] = 10000;
+    testSensor("MQ-4", -0.318, 1.133);
+
+    while(1);
 }
 
 

examples/MQ-4-LINEAR/MQ-4-LINEAR.ino

@@ -37,7 +37,7 @@ void setup() {
   Serial.begin(9600); //Init serial port
 
   //Set math model to calculate the PPM concentration and the value of constants
-  MQ4.setRegressionMethod(0); //_PPM =  a*ratio + b
+  MQ4.setRegressionMethod(0); //_PPM =  pow(10, (log10(ratio)-b)/a)
 
   
   

src/MQUnifiedsensor.cpp

@@ -112,9 +112,9 @@ float MQUnifiedsensor::validateEcuation(float ratioInput)
   if(_regressionMethod == 1) _PPM= _a*pow(ratioInput, _b);
   else 
   {
-    // https://jayconsystems.com/blog/understanding-a-gas-sensor
-    double ppm_log = (log10(_ratio)-_b)/_a; //Get ppm value in linear scale according to the the ratio value  
-    _PPM = pow(10, ppm_log); //Convert ppm value to log scale  
+      // https://jayconsystems.com/blog/understanding-a-gas-sensor
+      double ppm_log = (log10(ratioInput)-_b)/_a; //Get ppm value in linear scale according to the the ratio value  
+      _PPM = pow(10, ppm_log); //Convert ppm value to log scale  
   }
   //Serial.println("Regression Method: "); Serial.println(_regressionMethod);
   //Serial.println("Result: "); Serial.println(_PPM);