For the first of my lunch-time electronics projects, I’ve constructed an intruder alarm that can alert you any time somebody comes too close to your desk or cubicle. This project took me 45 minutes from start to finish including all coding, wiring and testing so, provided you’ve already got your lunch and eat it quickly, you too can be alerted to approaching co-workers before your lunch hour is up.

Using an Arduino for this project is overkill, as we could easily accomplish the same result without using a micro-controller at all, but it is a good introduction in using analogue electronics with the board.

In this project I’ve connected an ultrasonic range finder, a potentiometer and an LED to an Arduino to form a basic intruder alarm. The potentiometer acts as a threshold so you can easily tune the performance of the ultrasonic range finder to your local environment.

Very simply, every time the value from the ultrasonic range finder drops below the potentiometer’s threshold value, an alarm is triggered. In this case the alarm is an LED, but it could easily be a buzzer if you wanted to annoy your cubicle neighbours. If your Arduino is connected to a PC then you can also use the serial monitor to read the debug information of the two analogue devices.

This isn’t really a tutorial on how to use an Arduino but more of an example of what can be quickly accomplished by connecting a few simple components together and throwing a wee bit of code at a problem. If you want to build your own, or just look closer at how I built mine, keep reading for photos, BOMs,  Source Code and wiring diagrams.

Photo Gallery

Bill of Materials

 1 no. Arduino Diecimila       Available from Maplin         £24.99
 1 no. Ultrasonic Range Finder Available from CoolComponents £24.48
 1 no. 1 kΩ Linear Pot         Available from Maplin         £ 1.14
 1 no. 5mm Red LED             Available from Maplin         £ 0.64
 1 no. 220Ω Resistor           Available from Maplin         £ 0.36
12 no. Jump Lead               Available from Maplin         £16.99
 2 no. Mini Bread-board        Available from Maplin         £ 2.49

Arduino Sketch Source Code

Fritzing Schematic


One thought on “IntruderAlert

  1. Nice write up, always like it when folks provide part numbers or links to where to get the parts. Also like that you included the Fritzing diagram. Keep up the good work!

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