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IoTea: An internet-connected tea machine

TUTORIAL

number, as per the first example. Run the code. It

won’t do anything to begin with, but you can test each

item by typing pump.on(), pump.off() etc.

import gpiozero

pump = gpiozero.LED(3, active_high=False)

valve = gpiozero.LED(26)

kettle = gpiozero.LED(5)

button = gpiozero.button(2)

All this code does is set up each relay using the

gpiozero library, which makes it really easy to control

physical hardware with a Raspberry Pi. We’re using the

LED class for the relays because although they aren’t

LEDs, it allows us to turn them on and off, which is all

they really need to do. It also sets up the button. Make

sure everything works before moving on.

Once you’ve got the relays worked out, the next

step is to write an algorithm for making a cup of tea. It

basically consists of turning on each component of the

system for a length of time, one after the other.

def makeACuppa():

pump.on()

time.sleep(pumpdelay)

pump.off()

kettle.on()

time.sleep(kettledelay)

kettle.off()

valve.on()

time.sleep(valvedelay)

valve.off()

Variables are used here for the amounts of time,

because it makes it easier to change the delay times

later (there’s a fair bit of trial and error involved in that

stage!). When that code’s done, add the line button

when_pressed = makeACuppa to trigger the algorithm

when the button’s pressed. Run the code again and

try it (without any water in the system). This code

will work fine for simply making tea at the press of a

button, but if we want our tea to be cloud-connected

we need to add another block of code.

If This Then That (IFTTT) is a great service for IoT

projects – it ties together all sorts of online services.

However, it’s not too easy to integrate the output of

an IFTTT applet with a Python script without hosting

a full-blown web server, and that’s another level of

complication that this project could do without – so the

following steps use email as a way to get the internet

to talk to the Raspberry Pi. Set up a Gmail account for

your project with a unique email address (unless you

want a cup of tea every time you receive an email).

The code for this part is mostly the same as Adafruit’s

LED Email notifier project (hsmag.cc/jGEDcx), so

that’s a good place to go if you’re looking at making

modifications to this code.

You’ll need to install the IMAPClient library – use

sudo pip install imapclient in the Terminal to do

this. Then you’ll need to modify Adafruit’s code a bit:

remove all the references to RPi.GPIO and LEDs.

Replace the code in the if newmails > NEWMAIL_

OFFSET: section with makeACuppa() and delete the else

statement so it only makes you a cup of tea if a new

email’s detected.

You also need to replace the NEWMAIL_OFFSET variable

with one called prevMails, and assign that to the

number of new mails found every time the loop runs.

This is because you want it to run whenever there’s

a new email since the loop last ran, not whenever

you have any number of unread emails (a subtle but

important distinction!).

Finally, copy and paste the contents of the loop

above the code, so that when you run it, it checks the

number of emails to begin with and assigns that.

TAKING THINGS FURTHER

There are lots of ways this project could be improved. For example, if the water tank is

empty it could lead to the kettle boiling dry which isn’t a good idea – so perhaps a water

sensor could be added to alert you when it’s running out.

Another potential issue is that the system relies on the kettle being full to the bottom

of the valve before operation (any liquid under the valve level won’t be dispensed into

the cup), so maybe a liquid level sensor could be used to ensure the kettle is full enough.

The system as it stands will make a cup of tea whenever it receives an email (which

is open to hacks!), so it could be advantageous to refine the code to only make tea when

emails from a specific address are received.

You could also add a system to remove the teabag from the cup after a period of time.

There’s only one thing worse than no cup of tea, and that’s an over-brewed cup of tea!

It should go without saying that it’s important to make sure all electronics are suitable

for use in 100°C operation – if in doubt, don’t use it!

OPTIONS FOR ENHANCEMENT

Below

The kettle must be

kept filled to the

level just below the

bottom of the valve

The rc.local file

works for auto-

running scripts

on the Raspberry

Pi and is a useful

thing to keep handy.

There are also all

sorts of other ways

to do this including

using .bashrc,

crontab, and init.d.

QUICK TIP