MQ8 gas sensor

IT18203172/MQ-8_Sensor/MQ-8_Sensor.ino

+#define         MQ_PIN                       (0)     
+#define         RL_VALUE                     (10)   
+#define         RO_CLEAN_AIR_FACTOR          (9.21)                                                    
+#define         CALIBARAION_SAMPLE_TIMES     (50)    
+#define         CALIBRATION_SAMPLE_INTERVAL  (500)                                                      
+#define         READ_SAMPLE_INTERVAL         (50)    
+#define         READ_SAMPLE_TIMES            (5)                                                         
+#define         GAS_H2                      (0)
+ 
+float           H2Curve[3]  =  {2.3, 0.93,-1.44};    
+                                                                                                                                                            
+float           Ro           =  10;                  
+ 
+void setup() {
+  Serial.begin(9600);                               
+  Serial.print("Calibrating...\n");                
+  Ro = MQCalibration(MQ_PIN);                       
+                                                                   
+  Serial.print("Calibration is done...\n"); 
+  Serial.print("Ro=");
+  Serial.print(Ro);
+  Serial.print("kohm");
+  Serial.print("\n");
+}
+ 
+void loop() {
+   Serial.print("H2 Concentration:"); 
+   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_H2) );
+   Serial.print( "ppm" );
+   Serial.print("\n");
+   delay(200);
+}
+ 
+
+float MQResistanceCalculation(int raw_adc) {
+  return ( ((float)RL_VALUE*(1023-raw_adc)/raw_adc));
+}
+ 
+
+float MQCalibration(int mq_pin) {
+  int i;
+  float val=0;
+ 
+  for (i=0;i<CALIBARAION_SAMPLE_TIMES;i++) {            
+    val += MQResistanceCalculation(analogRead(mq_pin));
+    delay(CALIBRATION_SAMPLE_INTERVAL);
+  }
+  val = val/CALIBARAION_SAMPLE_TIMES;                  
+ 
+  val = val/RO_CLEAN_AIR_FACTOR;                       
+                                                       
+  return val; 
+}
+
+float MQRead(int mq_pin) {
+  int i;
+  float rs=0;
+ 
+  for (i=0;i<READ_SAMPLE_TIMES;i++) {
+    rs += MQResistanceCalculation(analogRead(mq_pin));
+    delay(READ_SAMPLE_INTERVAL);
+  }
+ 
+  rs = rs/READ_SAMPLE_TIMES;
+ 
+  return rs;  
+}
+ 
+int MQGetGasPercentage(float rs_ro_ratio, int gas_id) {
+  if ( gas_id == GAS_H2) {
+     return MQGetPercentage(rs_ro_ratio,H2Curve);
+  }  
+  return 0;
+}
+ 
+int  MQGetPercentage(float rs_ro_ratio, float *pcurve) {
+  return (pow(10,( ((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
+}