This library is made for MQ-4 gás sensor.
Dependents: MQ4_example Navitec-Firmware
MQ4.cpp
- Committer:
- renanbmx123
- Date:
- 2018-07-17
- Revision:
- 0:401959f72658
- Child:
- 1:d64cac41351a
File content as of revision 0:401959f72658:
#include "MQ4.h" void MQ4::begin(){ Ro = MQCalibration(); } /* * Reads data from MQ4. * * Param data: the pointer to fill. */ void MQ4::read(MQ4_data_t *data){ data->lpg = MQGetGasPercentage(MQRead()/Ro,GAS_LPG); data->h2 = MQGetGasPercentage(MQRead()/Ro,GAS_H2); data->ch4 = MQGetGasPercentage(MQRead()/Ro,GAS_CH4); } /* * reads data, returns LPG value in ppm */ float MQ4::readLPG(){ return MQGetGasPercentage(MQRead()/Ro,GAS_LPG); } /* * reads data, returns H2 value in ppm */ float MQ4::readH2(){ return MQGetGasPercentage(MQRead()/Ro,GAS_H2); } /* * reads data, returns CH4 value in ppm */ float MQ4::readCH4(){ return MQGetGasPercentage(MQRead()/Ro,GAS_CH4); } /****************** MQResistanceCalculation **************************************** Input: raw_adc - raw value read from adc, which represents the voltage Output: the calculated sensor resistance Remarks: The sensor and the load resistor forms a voltage divider. Given the voltage across the load resistor and its resistance, the resistance of the sensor could be derived. ************************************************************************************/ float MQ4::MQResistanceCalculation(int raw_adc) { return (((float)RL_VALUE*(1023-raw_adc)/raw_adc)); } /***************************** MQCalibration **************************************** Input: mq_pin - analog channel Output: Ro of the sensor Remarks: This function assumes that the sensor is in clean air. It use MQResistanceCalculation to calculates the sensor resistance in clean air and then divides it with RO_CLEAN_AIR_FACTOR. RO_CLEAN_AIR_FACTOR is about 10, which differs slightly between different sensors. ************************************************************************************/ float MQ4::MQCalibration() { // This should be done in 'clean air' float val=0; for (int i=0;i<CALIBARAION_SAMPLE_TIMES;i++) { //take multiple samples val += MQResistanceCalculation(_pin.read_u16()>>6); wait_ms(CALIBRATION_SAMPLE_INTERVAL); } val = val/CALIBARAION_SAMPLE_TIMES; //calculate the average value val = val/RO_CLEAN_AIR_FACTOR; //divided by RO_CLEAN_AIR_FACTOR yields the Ro according to the chart in the datasheet return val; } /***************************** MQRead ********************************************* Input: mq_pin - analog channel Output: Rs of the sensor Remarks: This function use MQResistanceCalculation to caculate the sensor resistenc (Rs). The Rs changes as the sensor is in the different consentration of the target gas. The sample times and the time interval between samples could be configured by changing the definition of the macros. ************************************************************************************/ float MQ4::MQRead() { int i; float rs=0; for (i=0;i<READ_SAMPLE_TIMES;i++) { rs += MQResistanceCalculation(_pin.read_u16()>>6); wait_ms(READ_SAMPLE_INTERVAL); } rs = rs/READ_SAMPLE_TIMES; return rs; } /***************************** MQGetGasPercentage ********************************** Input: rs_ro_ratio - Rs divided by Ro gas_id - target gas type Output: ppm of the target gas Remarks: This function passes different curves to the MQGetPercentage function which calculates the ppm (parts per million) of the target gas. ************************************************************************************/ float MQ4::MQGetGasPercentage(float rs_ro_ratio, GasType gas_id) { switch(gas_id) { case GAS_LPG: return MQGetPercentage(rs_ro_ratio,LPGCurve); case GAS_H2: return MQGetPercentage(rs_ro_ratio,H2Curve); case GAS_CH4: return MQGetPercentage(rs_ro_ratio,CH4Curve); default: return -1.0; } } /***************************** MQGetPercentage ********************************** Input: rs_ro_ratio - Rs divided by Ro pcurve - pointer to the curve of the target gas Output: ppm of the target gas Remarks: By using the slope and a point of the line. The x(logarithmic value of ppm) of the line could be derived if y(rs_ro_ratio) is provided. As it is a logarithmic coordinate, power of 10 is used to convert the result to non-logarithmic value. ************************************************************************************/ int MQ4::MQGetPercentage(float rs_ro_ratio, float *pcurve) { return (pow(10,(((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0]))); } // Return Ro calculated; float MQ4::get_Ro() { return Ro; }