3

FORGE

Once you’ve connected everything up, the next step

is to attach the valve to the kettle. The valve you use

has a big impact on what bits you need to connect

it – the best thing to do is go to a physical shop and try

different bits until you have a setup you’re happy with.

We ended up using two 15 mm nuts with rubber seals

to connect the valve to the kettle, and a right-angle

15 mm tap connector to add a small spout to the ‘out’

side of the valve, which directs the water into a cup –

but it depends on the valve you get, and how big a hole

you want to make in the kettle. It’s a good idea to use

metal fittings so you can be sure they won’t melt.

Next, drill a hole in the side of the kettle to

accommodate the fittings for the valve. A stepped-

cone drill bit is the best way to do this. If your kettle

is plastic, it’s important to take things slowly and be

careful because the plastic cracks incredibly easily, and

if that happens it’ll ruin the whole kettle. Once you’ve

drilled the hole, fit the valve. Use a mole wrench or

spanner to tighten up the nuts really well – but not too

far or you’ll risk cracking the plastic.

Once everything’s connected up, it’s time to

program. Flash an SD card with Raspbian OS (there’s

a tutorial for this on the Raspberry Pi website at

hsmag.cc/UPSBIK), connect the Pi to a screen,

power supply, mouse and keyboard (you’ll need a USB

hub and a few adapters), and boot up. Note that you

absolutely mustn’t connect the 12 V power supply

whilst you’ve got your Raspberry Pi connected to

another power supply, or bad things will happen!

DON’T BAKE THE PI

The first step is going to be testing all the relays and

valves thoroughly. Fire up a Python IDE window (under

Raspberry Menu > Programming), and then open a

new window (File > New window).

Type the following code – if any of your relays

were active low, you’ll need to add the code

active_high=False in the brackets after the pin

TAKING THE (BEEF)CAKE
Once you’ve worked the valve out, it’s time to
do the same for the relays. You’ll need to solder
the Beefcake relay kit using the instructions on
SparkFun’s website at hsmag.cc/RKjTYl. It might
seem a little counter-intuitive to use two different
types of relay, but relays which can handle the full
13 A a kettle draws whilst boiling aren’t too common,
and it’s one place you really don’t want to be cutting
corners. You’ll need to work out if the relays are
active-high (if they turn on when their control pin
is connected to 3.3 V), or active-low (if they turn on
when their control pin is connected to ground). Keep
a note of which each one is – you’ll need to use it
when programming later.
The next step is to connect everything up according
to the diagram on the following spread. You’ll want to
solder wires directly to the GPIO of the Pi Zero W (no
header attached). Mount the 5 V regulator on a piece
of stripboard, and mark on which pins are for input
voltage, output voltage, and ground (you can find this
info by reading the data sheet for your regulator –
search for the name of the part). You should also use
a heatsink, and add capacitors to either side of your
regulator to smooth the voltage in case of any spikes;
the data sheet should have information on what’s
required. You’ll need to solder the connections to the
valve and pump, and use the screw terminals on the
relay for the rest. Leave out the kettle wire to begin
with, as it’s easier to test it without the relay.

YOU’LL NEED

Raspberry Pi

Zero W

A pair of low-

voltage relays

boardsebay.co.uk

A SparkFun

Beefcake relay

sparkfun.com

A kettle (the

simpler the better)

A water

container

2 V Solenoid

valve suitable for

100°C use

Small peristaltic

water pump

hsmag.cc/xmHijt

Small push-

button

5 V voltage

regulator

12 V power

supply (at least 3 A)

A small piece of

stripboard

Plenty of wire

The necessary

plumbing fittings

to connect your

valve to a kettle

and have it pour

into a cup

Below

Colour-coding wires is a great way to simplify things when

working on complex projects like this

Above

The Beefcake Relay kit is good fun to assemble, but you’ll need

a meaty soldering iron to make sure there’s a good connection

on the relay terminals