The MagPi - February 2020

Pi. As a small buzzer may not be particularly

deterring to a would-be room invader, we’ve

chosen a 120 dB siren that requires more current

that our Raspberry Pi can safely handle. So, we

will give the siren its own power supply and

safely control it using one of the Automation

HAT’s relays.

02

Prepare your Raspberry Pi

It’s up to you what model of Raspberry

Pi you use for this project. A Raspberry Pi Zero

W is more than capable of running the code and

we originally prototyped our guard using one. If

you’re thinking of getting clever, though, such

as adding facial recognition using a camera, you

might want to go for the horsepower of a Raspberry

Pi 4. Either way, start by attaching the Automation

HAT carefully to the GPIO header, and secure

with the provided standoff posts on the opposite

side to ensure the HAT doesn’t wiggle about and

come loose.

03

Set up the software

We’re going to use Raspbian Buster Lite as

the operating system as there’s no need for a user

interface, just a basic command-line operating

system. That said, there’s no harm in installing

the full version if you’re more comfortable with

that. Download the image from magpi.cc/raspbian

and flash to a microSD card. Now, as ever, it’s

time to log in and update everything with sudo apt

update && sudo apt upgrade. Once finished, run

sudo raspi-config and set up networking (if using

WiFi). Now, install the Automation HAT software

by running the following command:

Protect your stuff from nosey parents, annoying siblings, or

your nemesis with this easy-to-build motion-detection alarm

I

f you’re just getting into making with

Raspberry Pi, this tutorial is a great example

of using our favourite little computer for

physical computing, reacting to inputs, and

doing something useful with the results. It also

demonstrates some of the challenges you may

face when handling different types of voltage and

current. Here you’ll learn how to make a simple

motion detector that triggers a siren and sends

an alert to your smartphone when it’s triggered.

You can then make the project your own through

experimenting and adding more features.

01

Why an Automation HAT?

Many Raspberry Pi physical computing

projects directly use the GPIO to connect things

like sensors, buzzers, and LEDs. In this case,

we’re going use the incredibly versatile Pimoroni

Automation HAT. This ‘input expander’ allows

us to control devices that would normally either

be incompatible or even damage your Raspberry

PJ

Evans

A writer, developer,

tinkerer, and Milton

Keynes Raspberry

Jam wrangler. His

cat keeps setting the

siren off.

@mrpjevans

MAKER

Build an internet-

connected room guard

You’ll Need

> 12 V indoor siren

and PSU

magpi.cc/siren

> HC-SR501 PIR

sensor

magpi.cc/pir

> Automation HAT

magpi.cc/

automationhat

> Camera Module

(optional)

magpi.cc/camera Figure 1 The PIR sensor’s potentiometers (orange). Adjust

carefully with a small screwdriver, as they can be fragile

Warning!

Loud noise!

The siren used in this

tutorial is very loud

(120 dB). Always use ear

protection when testing.

TUTORIAL

42 magpi.cc Build an internet-connected room guard