diff --git a/examples/MQ-135-CorrectionFactorDHT11/MQ-135-CorrectionFactorDHT11.ino b/examples/MQ-135-CorrectionFactorDHT11/MQ-135-CorrectionFactorDHT11.ino new file mode 100644 index 0000000..0bbe622 --- /dev/null +++ b/examples/MQ-135-CorrectionFactorDHT11/MQ-135-CorrectionFactorDHT11.ino @@ -0,0 +1,183 @@ +/* + MQUnifiedsensor Library - reading an MQ135 + + Demonstrates the use a MQ135 sensor. + Library originally added 01 may 2019 + by Miguel A Califa, Yersson Carrillo, Ghiordy Contreras, Mario Rodriguez + + Added example + modified 23 May 2019 + by Miguel Califa + + Updated library usage + modified 26 March 2020 + by Miguel Califa + + Wiring: + https://github.com/miguel5612/MQSensorsLib_Docs/blob/master/static/img/MQ_Arduino.PNG + Please take care, arduino A0 pin represent the analog input configured on #define pin + + This example code is in the public domain. + +*/ + +//Include the library +#include +#include +#include +#include + +//Definitions +#define placa "Arduino UNO" +#define Voltage_Resolution 5 +#define pin A0 //Analog input 0 of your arduino +#define type "MQ-135" //MQ135 +#define ADC_Bit_Resolution 10 // For arduino UNO/MEGA/NANO +#define RatioMQ135CleanAir 3.6//RS / R0 = 3.6 ppm +//#define calibration_button 13 //Pin to calibrate your sensor + +#define MQ135_DEFAULTPPM 399 //default ppm of CO2 for calibration +#define MQ135_DEFAULTRO 68550 //default Ro for MQ135_DEFAULTPPM ppm of CO2 +#define MQ135_SCALINGFACTOR 116.6020682 //CO2 gas value +#define MQ135_EXPONENT -2.769034857 //CO2 gas value +#define MQ135_MAXRSRO 2.428 //for CO2 +#define MQ135_MINRSRO 0.358 //for CO2 + + +/// Parameters for calculating ppm of CO2 from sensor resistance +#define PARA 116.6020682 +#define PARB 2.769034857 + +/// Parameters to model temperature and humidity dependence +#define CORA 0.00035 +#define CORB 0.02718 +#define CORC 1.39538 +#define CORD 0.0018 + +#define DHTPIN 2 // Digital pin connected to the DHT sensor +// Feather HUZZAH ESP8266 note: use pins 3, 4, 5, 12, 13 or 14 -- +// Pin 15 can work but DHT must be disconnected during program upload. + +// Uncomment the type of sensor in use: +//#define DHTTYPE DHT11 // DHT 11 +#define DHTTYPE DHT22 // DHT 22 (AM2302) +//#define DHTTYPE DHT21 // DHT 21 (AM2301) + +// See guide for details on sensor wiring and usage: +// https://learn.adafruit.com/dht/overview + +DHT_Unified dht(DHTPIN, DHTTYPE); + +uint32_t delayMS; + +//Declare Sensor +MQUnifiedsensor MQ135(placa, Voltage_Resolution, ADC_Bit_Resolution, pin, type); + +void setup() { + //Init the serial port communication - to debug the library + Serial.begin(9600); //Init serial port + dht.begin(); + sensor_t sensor; + + //Set math model to calculate the PPM concentration and the value of constants + MQ135.setRegressionMethod(1); //_PPM = a*ratio^b + MQ135.setA(102.2); MQ135.setB(-2.473); // Configurate the ecuation values to get NH4 concentration + + /* + Exponential regression: + GAS | a | b + CO | 605.18 | -3.937 + Alcohol | 77.255 | -3.18 + CO2 | 110.47 | -2.862 + Tolueno | 44.947 | -3.445 + NH4 | 102.2 | -2.473 + Acetona | 34.668 | -3.369 + */ + + /***************************** MQ Init ********************************************/ + //Remarks: Configure the pin of arduino as input. + /************************************************************************************/ + MQ135.init(); + /* + //If the RL value is different from 10K please assign your RL value with the following method: + MQ135.setRL(10); + */ + /***************************** MQ CAlibration ********************************************/ + // Explanation: + // In this routine the sensor will measure the resistance of the sensor supposing before was pre-heated + // and now is on clean air (Calibration conditions), and it will setup R0 value. + // We recomend execute this routine only on setup or on the laboratory and save on the eeprom of your arduino + // This routine not need to execute to every restart, you can load your R0 if you know the value + // Acknowledgements: https://jayconsystems.com/blog/understanding-a-gas-sensor + Serial.print("Calibrating please wait."); + float calcR0 = 0; + for(int i = 1; i<=10; i ++) + { + MQ135.update(); // Update data, the arduino will be read the voltage on the analog pin + calcR0 += MQ135.calibrate(RatioMQ135CleanAir); + Serial.print("."); + } + MQ135.setR0(calcR0/10); + Serial.println(" done!."); + + if(isinf(calcR0)) {Serial.println("Warning: Conection issue founded, R0 is infite (Open circuit detected) please check your wiring and supply"); while(1);} + if(calcR0 == 0){Serial.println("Warning: Conection issue founded, R0 is zero (Analog pin with short circuit to ground) please check your wiring and supply"); while(1);} + /***************************** MQ CAlibration ********************************************/ + MQ135.serialDebug(true); + // Set delay between sensor readings based on sensor details. + delayMS = sensor.min_delay / 1000; +} + +void loop() { + + delay(delayMS); //Sampling frequency + + // if you want to apply corelation factor, you will add in this program the temperature and humidity sensor + sensors_event_t event; + dht.temperature().getEvent(&event); + float cFactor = 0; + if (!isnan(event.temperature) && !isnan(event.relative_humidity)) cFactor = getCorrectionFactor(event.temperature, event.relative_humidity); + Serial.print("Correction Factor: "); Serial.println(cFactor); + MQ135.update(); // Update data, the arduino will be read the voltage on the analog pin + MQ135.readSensor(false, cFactor); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup + MQ135.serialDebug(); // Will print the table on the serial port + +} + +/**************************************************************************/ +/*! +@brief Get the correction factor to correct for temperature and humidity +@param[in] t The ambient air temperature +@param[in] h The relative humidity +@return The calculated correction factor +*/ +/**************************************************************************/ +float getCorrectionFactor(float t, float h) { + return CORA * t * t - CORB * t + CORC - (h-33.)*CORD; +} + +/**************************************************************************/ +/*! +@brief Get the resistance of the sensor, ie. the measurement value corrected + for temp/hum +@param[in] t The ambient air temperature +@param[in] h The relative humidity +@return The corrected sensor resistance kOhm +*/ +/**************************************************************************/ +float getCorrectedResistance(long resvalue, float t, float h) { + return resvalue/getCorrectionFactor(t, h); +} + +/**************************************************************************/ +/*! +@brief Get the ppm of CO2 sensed (assuming only CO2 in the air), corrected + for temp/hum +@param[in] t The ambient air temperature +@param[in] h The relative humidity +@return The ppm of CO2 in the air +*/ +/**************************************************************************/ +float getCorrectedPPM(long resvalue,float t, float h, long ro) { + return PARA * pow((getCorrectedResistance(resvalue, t, h)/ro), -PARB); +}