Build a Motion Sensor Camera

Introduction

In this example you combine a passive infrared (PIR) sensor with a Raspberry Pi Camera Board to build a motion sensor camera. A PIR sensor measures infrared light radiating from objects. The sensor detects the change in the infrared radiation and triggers an alarm if the gradient of the change is higher than a predefined value. You connect the PIR sensor to one of the digital input pins of the Raspberry Pi hardware and monitor the output of the PIR sensor. When PIR sensor detects motion it outputs a logic high value. When you detect a logic high value on the digital input pin, you take a picture and save it on the host computer.

Prerequisites

It is helpful to complete the following examples

Required Hardware

To run this example you need the following hardware:

Connect PIR Motion Sensors

A PIR sensor has three pins: VCC, GND, and OUT. You connect the VCC pin to +3.3 Volt voltage rail and the GND pin to the ground. The OUT pin is the logic signal indicating motion. This pin will be connected to a GPIO pin on the Raspberry Pi hardware as shown in the following circuit diagram.

If you do not have a motion sensor available, you can substitute a push button instead. See Working with Raspberry Pi Hardware example for details.

Test Motion Sensor

When motion sensor detects movement, an LED on the sensor board turns
on. Move your hand in front of the PIR motion sensor and make sure the
sensor responds by turning on an LED. Then, execute the following at the
MATLAB prompt.

clear rpi
rpi = raspi();
motionDetected = readDigitalPin(rpi, 23);
disp(motionDetected);

The displayed value of the variable motionDetected should be one. The PIR motion detector holds the value of the OUT pin at logic high for approximately 5 seconds. Wait until the PIR sensor LED goes off and execute the preceding MATLAB code again. This time, you should observe a value of zero for the displayed value of motionDetected.

Test Camera Board

Create a camera board object by executing the following command on the MATLAB prompt.

cam = cameraboard(rpi);

The cam is a handle to a cameraboard object. Display an image captured from Camera Board in MATLAB.

img = snapshot(cam);
imagesc(img);

Note: You can also use the webcam API to create a webcam object.

Motion Sensor Camera

Run the motion sensor camera code by executing the following MATLAB commands.

N = 100;
delay = 0.1;
frameNo = 0;
for i = 1:N
    motionDetected = readDigitalPin(rpi, 23);
    if motionDetected
       fprintf('Motion detected on %s\n', datestr(now));
       img = snapshot(cam);
       image(img);
       drawnow;
       imwrite(img, sprintf('image%d.jpg', frameNo));
       % Wait until the motion detector output goes low
       pause(5);
    end
    pause(delay);
end

Summary

This example showed how to use a PIR motion sensor and a Raspberry Pi Camera Board to build a motion sensor camera.