3

FORGE

CHECKING IT WORKS
Once everything has been built, powered up and
programmed, it’s time to check it works. This is best
done before installing in the airing cupboard and with
the Pi Zero attached to a monitor and keyboard.
Run the script using this command:
python /home/pi/python/hotwater.py

You should see the information from each sensor
being printed to the screen, followed by messages
about the data being uploaded to Google.
Once everything is working when you run the script
manually, the final step is to have it run automatically
at regular intervals. The nice thing is that the Raspbian
operating system already has a built-in utility to do
just this: crontab.

CRONTAB IS YOUR FRIEND
Crontab is a Linux utility for automatically performing
tasks – either at fixed times of the day, or at boot –
but most importantly here, at regular intervals.
Crontab is opened using the following command:
crontab -e

You will see a text file in the standard Linux text

editor. Scroll to the end, and on a new line add

the following:

*/5 * * * * python /home/pi/python/hotwater.py &

This will automatically run the script every five

minutes. If you want a different frequency, then

change the number at the beginning.

You should now be able to open the Google Sheet

on another computer and watch the data come in

live every five minutes!

THE FINAL STEP

When everything is working correctly on the bench,

it’s time to fit the system into the airing cupboard

and the sensors to the hot water tank.

Starting at the mark made for the first sensor

location, use a blunt tool (a wooden skewer is ideal)

to poke a hole in the hot water cylinder insulation.

Wiggle it slightly to enlarge the hole until it is a little

smaller than the diameter of one of the temperature

sensors. Make sure the hole has passed all the

way to the copper wall of the internal cylinder

and that the insulation is scraped away from the

metal surface.

Put a blob of thermal paste about the size of a

small pea on the tip of the sensor and push it into

the hole until it makes contact with the cylinder wall.

The insulation layer should hold it in place.

Once everything is in, make sure all sensors are

reading approximately the same value when you

know the water is fully hot (within around 1°C).

If one is noticeably different, ensure there is no

remaining insulation between the sensor and tank

wall and make sure you have used enough thermal

compound to fill any air gaps.

That’s all there is to it. You can now monitor your

hot water system from wherever you are and you’ll

never have to endure a cold shower again.

TROUBLE SHOOTING

If you are experiencing issues, check the following:

• The Google Sheet has the correct name and
  has been shared with the email address
  generated by the Google Developers Console


• The client_secret.json file is in the correct place^


• The codes for each of the eight sensors are
  correctly identified and entered into the script

WHAT TO CHECK

Only poke holes in

the insulation with

something soft that

will not damage the

internal cylinder

(avoid anything

made of metal).

QUICK TIP

Above

DS18B20 temperature sensors are available in waterproof

packages like this or three pin packages for more

confined spaces