D-4 Motion Sensor Code

Next, you'll add code in your Smart Security device app to control the motion sensor.

The basic steps to use a motion sensor in your app code are:

1. Declare a global variable to store the I/O pin number for the motion sensor.

2. Set the pin mode for the motion sensor pin in the setup() function.

3. Use a digitalRead() statement to check whether the sensor detects any motion, and add code statements that should be performed if motion is detected (or not detected).

Global Variable for Sensor

Declare a global variable to store the I/O pin number for the motion sensor by adding this code statement before the setup() function:

int motion = D3;

If you connected your motion sensor to a different I/O pin other than D3, then modify this code statement to list the correct pin number for your motion sensor.

Set Pin Mode for Sensor

Set the pin mode for your motion sensor pin by adding this code statement within the setup() function (between the curly braces):

pinMode(motion, INPUT_PULLUP);

Add Function to Check Sensor

The digitalRead() method is used to check whether the sensor currently detects any motion.

The digitalRead() method will return a value of either HIGH or LOW (which are treated as if they were int values):

• HIGH indicates that motion is NOT currently detected.

• LOW indicates that motion is currently detected.

A variable named motionState will store the value returned by the digitalRead() method.

An if statement will be used to perform a set of actions if motion is detected (if motionState has a value equivalent to LOW).

You'll add a custom function named checkMotion() that will contain all this code.

Add this checkMotion() custom function after the loop() function (you can add it before or after the toggleMode() function):

void checkMotion() {
    int motionState = digitalRead(motion);
    
    if (motionState == LOW) {
        // add code to do something if motion detected
        
        delay(2000); // wait 2 seconds before checking sensor again
    }
}

Inside the if statement, you'll need to add code to do something if motion is detected. In the next step of this tutorial, you'll add code here to make an "alarm sound" using the speaker. Later, you'll also add code to send an event notification to the web app that you'll be creating.

You'll notice that a delay() of 2 seconds is performed when motion is detected. This delay is needed to allow the sensor to capture a new "snapshot" of the environment before checking the sensor again.

Call Function in Loop If Armed

The checkMotion() function will only be performed if it is called within another function, such as the loop() function. However, the motion sensor should only be checked if the device's mode is currently set to "armed".

Add this code within the loop() function (after the closing curly brace of the existing if statement that checks the value of buttonState):

    if (deviceMode == "armed") {
        checkMotion();
    }

This code will only call the checkMotion() function if the value of deviceMode is equivalent to "armed".

Save your smart-security app code by clicking the Save icon in the left navigation bar.

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