What do we need to create an IoT Arduino sensor project?

Step 1: Arduino Sensor Circuit

As our gas sensor, we will use an MQ-4 sensor. It is a fast and reliable sensor that's very sensitive to natural gas and CH4 (Methane). It has a long life and is commonly used in gas leakage detecting. What we want to do is create a simple project that shows gas concentration using two LEDs:

• Green Led: The gas concentration is under the threshold.
• Red Led: Alert! The gas concentration is above the threshold.

The MQ-4 Arduino sensor has four pins:

• Vcc (+5V)
• Ground
• Digital output
• Analog output

We will use the analog output to check the gas concentration. The schematic is shown below:

Please notice that the connections to the gas sensor in the schematic above are not real, while the Arduino pin used to get data from the sensor is the real one (A5).

When you turn on the gas sensor at the beginning, it could smell a bit. This is normal — do not worry. In the schematic, there are two resistors that connect the Arduino digital pin and the LEDs. These limit the current flowing through the LEDs. They are 220 Ohm. That’s all. You are ready now to develop the sketch to monitor the Arduino sensor.

Step 2: Develop the Arduino Sketch

The sketch below describes how to implement the gas monitoring system:

int pinRedLed = 11;
int pinGreenLed = 8;
int pinSensor = A5;
int THRESHOLD = 250;
void setup() {
    pinMode(pinRedLed, OUTPUT);
    pinMode(pinGreenLed, OUTPUT);
    pinMode(pinSensor, INPUT);
    Serial.begin(9600);
}

void loop() {
    int analogValue = analogRead(pinSensor);
    Serial.println("Val: " + analogValue);
    digitalWrite(pinGreenLed, HIGH);
    if (analogValue >= THRESHOLD) {
        digitalWrite(pinGreenLed, LOW);
        digitalWrite(pinRedLed, HIGH);
    }
    else {
        digitalWrite(pinRedLed, LOW);
    }
    delay(5000);
}

The code is very simple. At the beginning, it declares the pins we will use to connect to the sensor and LEDs. The green LED is always on while the red LED turns on only when the gas concentration is over the threshold.

Step 3: Implement the Notification

In this last step, we will implement a notification system so that when the gas concentration is over the threshold, we will get an email. To do it, this Arduino sensor sketch uses IFTTT. IFTTT stands for If This Then That. It's a powerful system that helps us connect to countless services, like social services. The first step is creating an account — if this is the first time you've used this service.

Once you have your account, click on search at the top and look for the maker service. This service is made for makers that want to integrate external services with Arduino or similar boards:

Now go to Applet and create a new Applet. Click on the plus sign and add the service. In this case, you should add a Maker service to the one we created before. Click on Receive a Web Request and configure your trigger. This is the event that triggers the notification process, in other words, as soon as IFTTT receive a web request, it sends an email:

Create the trigger. Now we have to configure the other step: the service that should be executed when the trigger is fired. Click on the plus sign again (in the then part) and add the email service. You can add other services, too:

Add email details and confirm. At the end you, have your service configured in IFTTT:

That’s all. Now to trigger this event, we have to call the URL as shown in the service configuration. We have to modify the Arduino sketch to call the URL when the analog value goes above the threshold.

Conclusion

In the end, you have implemented a simple IoT project in just three steps. Integrating online services and Arduino, you can expand your Arduino and create interesting and useful IoT project with a few lines of code. In this tutorial, you learned how to create an IoT project that monitors an Arduino sensor.