MQ2.h

00001 #ifndef MQ2_h
00002 #define MQ2_h
00003 
00004 #include "mbed.h"
00005 
00006 #define RL_VALUE                    1                                           //define the load resistance on the board, in kilo ohms
00007 #define RO_DEFAULT                  10                                          //Ro is initialized to 10 kilo ohms
00008 #define RO_CLEAN_AIR_FACTOR         9.83f                                       //RO_CLEAR_AIR_FACTOR=(Sensor resistance in clean air)/RO, which is derived from the chart in datasheet
00009 #define CALIBARAION_SAMPLE_TIMES    5                                           //define how many samples you are going to take in the calibration phase
00010 #define CALIBRATION_SAMPLE_INTERVAL 50                                          //define the time interal(in milisecond) between each samples
00011 #define READ_SAMPLE_INTERVAL        50                                          //define how many samples you are going to take in normal operation
00012 #define READ_SAMPLE_TIMES           5                                           //define the time interal(in milisecond) between each samples
00013 
00014 //The curves
00015 static float LPGCurve[]   = {2.3f,0.21f,-0.47f};                                
00016 static float COCurve[]    = {2.3f,0.72f,-0.34f};
00017 static float SmokeCurve[] = {2.3f,0.53f,-0.44f};
00018 
00019 typedef struct {
00020   float lpg;
00021   float co;
00022   float smoke;
00023 } MQ2_data_t;
00024 
00025 typedef enum  {
00026     GAS_LPG = 0,
00027     GAS_CO = 1,
00028     GAS_SMOKE = 2
00029 } GasType;
00030 
00031 
00032 class MQ2 {
00033 public: 
00034     MQ2(PinName pin) : _pin(pin){
00035       Ro = RO_DEFAULT;
00036     };
00037     void read(MQ2_data_t *ptr);
00038     float readLPG();
00039     float readCO();
00040     float readSmoke();
00041     void begin();
00042 private:
00043     AnalogIn _pin;
00044     float MQRead();
00045     float MQGetGasPercentage(float rs_ro_ratio, GasType gas_id);
00046     int MQGetPercentage(float rs_ro_ratio, float *pcurve);
00047     float MQCalibration();
00048     float MQResistanceCalculation(int raw_adc);
00049     float Ro;
00050 };
00051 
00052 #endif