MQSensorsLib C++ Library

Sensor Connections

• VCC: Connect to 5V power supply (+).
• GND: Connect to GND ground (-).
• AO: Connect to the Analog Output of the sensor.

Note: If the sensor uses a different supply voltage than the ADC reference, use yourSensor.setVCC(<voltage>);.

Board Specifics

• Arduino: Standard analog connection. Note that MQ-7 and MQ-309A require two different voltages for the heater; these can be supplied via PWM or separate DC signals.
• ESP8266 / ESP32: Connect via analog pins as per board diagrams.
• ESP32 WROOM 32D: Does not require an external power supply. Connect A0 to PIN36, Vcc to 3v3, and GND to any GND port. (Note: If using WiFi, refer to the ESP2/ESP32_WROOM_32 folder for fixes).

You can enable detailed serial output to troubleshoot calculations and hardware/software characteristics. This is useful for seeing the library's internal steps and results.

1. In setup(), call MQx.serialDebug(true); (replace MQx with your sensor object).
2. In loop(), call MQx.serialDebug();.

Debug Output Colors:

• Yellow: Calibration status.
• Green: Hardware and software characteristics.
• Red: Library calculation headers.

// In setup
MQ2.serialDebug(true); 

// In loop
MQ2.serialDebug(); 

To account for environmental factors like temperature and humidity, the library allows for an optional "correction factor".

When the sensor datasheet provides coefficients for environmental compensation, you can pass this factor to the following functions:

• calibrate(float correctionFactor)
• readSensorR0Rs(float correctionFactor)

This allows you to adjust the sensor's sensitivity and baseline based on the current environmental conditions.

Clone the repository to your local machine to access the library and examples.

git clone https://github.com/miguel5612/MQSensorsLib

When using an MQ-3 sensor to read CH4, very high values passed to setA and setB can cause overflow errors (ovf).

To prevent this:

1. Use correct exponential notation: In C++, 2*10^31 is not the same as 2e31. Use 2e31 or pow(10, 31) for large coefficients.
2. Check float ranges: Ensure parameters do not exceed the maximum range of a float.
3. Library updates: If using version 3.0.0 or later, the library includes input validation, overflow prediction via logarithms, and double-precision calculations to mitigate this issue.

If the calibration process stops and displays a "Connection issue" message (specifically reported with the MQ-135 in clean air), follow these steps:

1. Verify physical connections: Check all wiring between the sensor and the microcontroller (Arduino/ESP32) to ensure there is no loose contact or short circuit.
2. Test with a basic sketch: Run a simple analog read program (without using this library) to confirm the sensor is providing varying voltage levels and is physically functional.
3. Check air quality: Ensure the sensor is actually being exposed to the expected environment (e.g., clean air for R0 calibration).

In older versions of the library, sensor resistance was calculated using _VOLT_RESOLUTION instead of the actual supply voltage.

To ensure accurate readings, use version 3.0.1 or later, which uses the actual VCC in its equations. You can manage the supply voltage using the following methods:

• setVCC(float voltage): Sets the actual supply voltage.
• getVCC(): Retrieves the current supply voltage setting.

// Example of setting the supply voltage for accurate calculations
sensor.setVCC(5.0);

Use these methods to retrieve the current configuration and calculated values:

• getA(): Returns coefficient a.
• getB(): Returns coefficient b.
• getR0(): Returns the current $R_0$ value.
• getRL(): Returns the load resistor value.
• getVCC(): Returns the sensor supply voltage.
• getVoltResolution(): Returns the voltage resolution.
• getRegressionMethod(): Returns the current regression method as a String.
• getVoltage(bool read = true, bool injected = false, int value = 0): Returns the voltage reading.
• getRS(): Returns the current $R_S$ value.

Use the following methods to configure the sensor's electrical and mathematical parameters before calling init() or update():

• setVCC(float vcc): Set the sensor supply voltage (default 5.0).
• setVoltResolution(float voltage_resolution): Set the voltage resolution (default 5.0).
• setPin(int pin): Set the analog pin number.
• setADC(int value): Set the ADC value (used primarily for externalADCUpdate).
• setRL(float RL): Set the load resistor value in KiloOhms (default 10).
• setR0(float R0): Set the $R_0$ value.
• setA(float a) and setB(float b): Set the coefficients for the regression model.
• setRegressionMethod(int regressionMethod): Choose the mathematical model:
  • 1: Exponential
  • 2: Linear
• serialDebug(bool onSetup): Enable serial output to show sensor information during setup.

To use the library, instantiate the MQUnifiedsensor class. You can provide the board type (e.g., "Arduino"), the voltage resolution (e.g., 5.0 or 3.3), the ADC bit resolution (e.g., 10 or 12), the analog pin, and the sensor type.

Available constructors:

• MQUnifiedsensor(String Placa = "Arduino", float Voltage_Resolution = 5, int ADC_Bit_Resolution = 10, int pin = 1, String type = "CUSTOM MQ")
• MQUnifiedsensor(String Placa = "Arduino", String type = "CUSTOM MQ")

// Example initialization for a 3.3V ESP32 with 12-bit ADC on pin 34
MQUnifiedsensor MQ( "ESP32", 3.3, 12, 34, "MQ2" );