9

TUTORIAL

Upgrade your humble letterbox with push notifications

Use a magnetic switch to find out when your postie’s been

Upgrade your humble

letterbox with push

notifications

ave you ever been eagerly waiting

for an item to arrive in the post,

and wished you could tell straight

away if it has finally arrived?

Maybe you’re out at work when the

postman comes, or your letterbox

is at the end of a really long driveway? Well, this is

the project for you – we’ll show you how to rig up a

tiny Raspberry Pi Zero, and a sensor switch, to send

a push notification to your phone every time the

letterbox flap is opened.

Before we get started, I’m going to assume that

you already have your Raspberry Pi Zero all set up,

with the latest version of Raspbian installed and up

to date, and the date and time correctly set. You’ll

also need a mini HDMI cable and a USB hub with a

micro USB connector, in order to plug in a keyboard

and mouse for the initial setup.

With that all ready, start by connecting up the

magnetic switch to the numbered GPIO pin 18 and

a ground pin – see the wiring diagram overleaf for

details. If you strip a short length from the ends of

your bell wire, this should easily slot into the female

DuPont cables, for easy connection to the GPIO

pins. The other end is wired into the sensor switch.

Wiring-wise, that’s it – it’s a very simple setup.

Connect the Pi to your home network, either

via WiFi or with a network cable, then enable SSH

access (Pi menu > Preferences > Raspberry Pi

configuration > Interfaces > SSH), so you can access

the Pi from another computer on your network

later. Determine the Pi’s IP address on your home

network by opening a Terminal and typing the

following command:

hostname -I

Now that’s all set up, you can start configuring the

vital services required to make things work and talk to

each other. This project works by adding a new row to

a Google spreadsheet each time the magnetic switch

is activated (i.e. the letterbox is opened), along with

the date and times that it was opened and closed.

Another service then monitors this sheet and sends

the alert to your phone whenever it sees that a new

row has been added.

Create a new Google Sheet and call it Letterbox

Activations. Set up three columns as headings, then

delete all other cells so that your sheet looks like the

image below. This is important, as the Python

H

Paul

Freeman-Powell

@paulfp

Paul is a technology

enthusiast, geek, video

producer, drummer,

cyclist, husband,

father to three children,

including twins, and host

of the award-winning

Switched On Network

YouTube channel. You

can find his website at

switchedonnetwork.com

Below

The blank Google Sheet, awaiting the first logs.

It’s important to remove all other rows, as I have done here