Arduino Motion Detector

How to build an Arduino Ultrasonic Motion Detector

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The full Arduino Motion Detector project update is published in issue #3 of the Home DIY Electronics Magazine so register and claim your copy now.

In the article: Arduino Distance Sensor How to Build I showed you how to hook up an Arduino Uno, an LCD/Keypad shield and an HC-SR04 Ultrasonic Echo module. By loading a little software code onto the Arduino you built a working Ultrasonic distance sensor.

The distance sensor was further developed in the article: Arduino Distance Sensor Part 2. The software sketch was updated to add more display modes and to introduce the use of the keypad on the shield to switch between modes.

In this article we take things a little further by adding an LED indicator and a new version of the software to add motion detection to the project. If you haven't already built the distance sensor then do it now because it is the starting point of the Motion Detector project.

Detection specification

There are a number of things that you need to think about before you begin to build any project. The most important question that must be answered is "What will it be used for"?

Your reason for building this may be different to mine but I'm working towards using this system as part of an animal deterrent to stop cats pooping in my yard.

I want to use the output to fire a battery operated water gun so that it soaks the cats and drives them away before they have time to leave me any unwanted packages.

Because I'm going to be firing a water gun with a limited supply of water, I can't afford to have it firing on false triggers too often. This would waste ammunition and battery power.

This means that I must manage the sensitivity carefully to make sure that it only fires when it should. A task that is easier said than done but I've had some success.

My cat repeller must work in daylight as well as at night in the dark. Traditional passive infra-red motion detectors are not very good at this.

They work by sensing heat from animals and humans so they can become much less sensitive on a bright hot day.

An ultrasonic sensor should be consistent day and night because it relies on sound waves rather than electromagnetic infra-red radiation.

So let's get started.