Do you have any data that would cause damage if it fell into the wrong hands? Or do you wish to know who enters a specific place when you're not present? Well, you can now easily answer these questions by building your own intruder detection system!

As mentioned before, this project uses an ultrasonic range sensor for the GrovePi and a PiCam to take pictures if any movement is detected by the ultrasonic ranger. Connect the ultrasonic ranger to port D4 of the Grove Pi, the buzzer to D5, the status LED to D3, and the Pi Camera to the port provided on the Raspberry Pi as learned in Chapter 4, Working with Webcam and Pi Camera. Following the theme of the book, we will first look at the whole code, and then learn what each statement does, line by line:

import picamera
import grovepi
from time import sleep

camera = picamera.PiCamera()
counter = 0
led = 3
buzzer = 5
ultrasonic = 4

while True:
    try:
        if grovepi.ultrasonicRead(ultrasonic) < 100:
        print 'Intruder Detected'
            grovepi.analogWrite(buzzer, 100)
            grovepi.digitalWrite(led, 1)
            sleep(.5)
            grovepi.analogWrite(buzzer, 0)
        grovepi.digitalWrite(led, 0)
            camera.capture('image' + counter + '.jpg')
            print 'Image Captured'
        sleep(2)
    except IOError:
        print "Error"

Save the preceding code as prog2.py and run it. Now, try to come in front of the ultrasonic sensor and you will see the output on the terminal, and have your picture taken as an intruder!

The code itself is very simple to understand, as it is just an amalgamation of parts from Chapter 4, Working with Webcam and Pi Camera, which we have already learned, and parts from the previous example. We start by importing the dependencies for the Pi Camera and GrovePi sensors.

As a setting-up step, we set the camera variable to be an object for our Pi Camera and it can be used to take pictures. We set a counter for the number of pictures and set the LED and buzzer to be used on ports D3 and D5 respectively. We also import the sleep method from the 'time' module to add delays. Like before, we include a 'try, except' block in the infinite while loop, so that when errors are encountered, it does not crash.

Basic algorithm for the intruder detection can be described as: Whenever anything comes in front of the ultrasonic ranger whose range is less than 100 cms, it means that there is an intruder. If the preceding condition is true, then sound the buzzer, light the LED, and take a picture. The ultrasonicRead() method from the GrovePi module reads the output from the ultrasonic ranger that is connected to port D7 of the GrovePi. If the distance is less than 100 cms, then we proceed to execute the intruder detection alarm procedure. First, we output Intruder detected to the terminal, then we turn on the buzzer by the analogWrite() method and the LED with the digitalWrite() method. The analogue write method takes the port number of the peripheral and a value from 0 to 255. The higher the value, the higher the intensity of the signal transmitted to the peripheral. The digitalWrite() method also takes the port number as an input and a binary number, to set the port high or low. We wait for half a second and then turn both the buzzer and LED off. Finally, we capture a photo with the camera pointed toward the direction of the ultrasonic ranger. Congratulations! We now have a photo of the intruder. Now, if we do not add some delay after taking a photo, the code will repeat itself and since the intruder is likely to still be there, the Raspberry Pi may take an unnecessarily large amount of photos. This is likely to burden the CPU and take resources away from other threads that might be running. So we add a two-second delay.

We can also experiment by varying the delay values to see what works best. I leave the reader with an interesting exercise of adding more peripherals to expand the functionality of the system, such as adding a keypad or a switch to turn off the system when it is not required.