Electrochemical Gas Sensors – Reading from multiple sensors

In this example, we demonstrate how to read from multiple sensors over I2C.

First, include the library and create the sensor objects by providing the configuration, the I2C address of the ADS1115, and the GPIO pin connected to the LMPEN pin on the breakout board:

// Include the required library
#include "Electrochemical-Gas-Sensor-SOLDERED.h"

// Create two different sensor objects
// Through the constructor, give them the configuration, 
// ADC I2C address and GPIO pin connected to the LMPEN pin
ElectrochemicalGasSensor sensorCO(SENSOR_CO, 0x4A, 25);
ElectrochemicalGasSensor sensorNO2(SENSOR_NO2, 0x49, 32);

ℹ️

We can change the I2C address of the ADS1115 ADC module by shorting jumpers on the breakout board. For more information on the jumpers look here

ℹ️

While the LMP91000 has a non-configurable I2C address, we can distinguish them by setting the LMPEN pin. When we want to configure a specific one, we can disable all the others by setting their LMPEN pin to HIGH via the GPIO pins while the one we want to configure stays at a HIGH state. More information about this can be found here

Next, in the setup() function, both sensors are initialized, along with the serial communication:

void setup()
{
    Serial.begin(115200); // For debugging

    // Init breakout #1
    if (!sensorCO.begin())
    {
        // Can't init? Notify the user and go to infinite loop
        Serial.println("ERROR: Can't init the sensor! Check connections!");
        while (true)
            delay(100);
    }

    Serial.println("CO sensor initialized successfully!");

    // Init breakout #2
    if (!sensorNO2.begin())
    {
        // Can't init? Notify the user and go to infinite loop
        Serial.println("ERROR: Can't init the sensor! Check connections!");
        while (true)
            delay(100);
    }

    Serial.println("NO2 sensor initialized successfully!");
}

sensor.begin()

Initializes the LMP91000 and ADS1115 on the board and establishes an I2C connection

Returns value: Boolean value, returns true if it was successful, false if it failed

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Getting readings

Finally, in the loop() function, we print the gas readings to the serial monitor:

void loop()
{
    // Make the reading of CO and print it
    double COreading = sensorCO.getPPM();

    // Print the reading with 5 digits of precision
    Serial.print("CO sensor reading: ");
    Serial.print(COreading, 5);
    Serial.println(" PPM");

    // Make the reading of NO2 and print it
    double NO2reading = sensorNO2.getPPB();

    // Print the reading with 5 digits of precision
    Serial.print("NO2 sensor reading: ");
    Serial.print(NO2reading, 5);
    Serial.println(" PPB");

    // Wait a bit before reading again
    delay(2500);
}

sensorCO.getPPM()

Make a measurement with the ADS1115 ADC and calculate the PPM value of the measured gas

Returns value: Double value, gas measurement in PPM (parts per million)

sensorNO2.getPPB()

Make a measurement with the ADS1115 ADC and calculate the PPB value of the measured gas

Returns value: Double value, gas measurement in PPB (parts per billion)

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Full example

See the full example here:

Measuring two sensors

Example of getting measurements from two sensors

// Include the required library
#include "Electrochemical-Gas-Sensor-SOLDERED.h"

// Create two different sensor objects
// Through the constructor, give them the configuration, 
// ADC I2C address and GPIO pin connected to the LMPEN pin
ElectrochemicalGasSensor sensorCO(SENSOR_CO, 0x4A, 25);
ElectrochemicalGasSensor sensorNO2(SENSOR_NO2, 0x49, 32);

void setup()
{
    Serial.begin(115200); // For debugging

    // Init breakout #1
    if (!sensorCO.begin())
    {
        // Can't init? Notify the user and go to infinite loop
        Serial.println("ERROR: Can't init the sensor! Check connections!");
        while (true)
            delay(100);
    }

    Serial.println("CO sensor initialized successfully!");

    // Init breakout #2
    if (!sensorNO2.begin())
    {
        // Can't init? Notify the user and go to infinite loop
        Serial.println("ERROR: Can't init the sensor! Check connections!");
        while (true)
            delay(100);
    }

    Serial.println("NO2 sensor initialized successfully!");
}

void loop()
{
    // Make the reading of CO and print it
    double COreading = sensorCO.getPPM();

    // Print the reading with 5 digits of precision
    Serial.print("CO sensor reading: ");
    Serial.print(COreading, 5);
    Serial.println(" PPM");

    // Make the reading of NO2 and print it
    double NO2reading = sensorNO2.getPPB();

    // Print the reading with 5 digits of precision
    Serial.print("NO2 sensor reading: ");
    Serial.print(NO2reading, 5);
    Serial.println(" PPB");

    // Wait a bit before reading again
    delay(2500);
}