The Tortoise Fridge project uses a Raspberry Pi to keep a critter safe during the winter months.

Seasonal temperature shifts can be a challenge for all living creatures. We humans can simply add or remove a jumper or vest, but our domestic companions don’t have that option.

Tech enthusiast Stefan Wollner encountered exactly this issue when he moved home in 2015 and realised the basement was too warm for his pet tortoise, Pumba.

This article was written by Rosie Hattersley and first appeared in The MagPi 79. Subscribe to our newsletter to get the free digital edition in your inbox every month. Or subscribe to the print edition of The MagPi.

See also:

Tortoise Fridge: temperature control for critters

Stefan had planned for the tortoise to spend the winter in a refrigerator – a common ploy for tortoise owners. However, the temperature of a standard refrigerator can’t be constantly monitored and the internal thermostat only provides a limited degree of temperature control. The warmest and coldest settings of an average fridge vary just three degrees Celsius.

In a flash of inspiration, Stefan realised that he could use a Raspberry Pi and a temperature sensor to keep watch on Pumba’s environment. For just a few euros, Stefan bought a DS18B20 temperature sensor to place inside the refrigerator. The system checks the temperature once a minute and records the results in a database, which it then displays as a real-time graph. The sensor’s findings are then acted upon by a cooling compressor connected to a 12 V-to-230 V switching relay, operated by the Raspberry Pi.

Two small Pi-powered displays visually confirm everything is working as it should. One two-line display shows the fridge’s current temperature and the temperature of the basement; the other displays the time the refrigerator was last opened, and the current status of the cooling compressor.

Whenever someone visits the basement, the backlight of both displays is activated by a PIR motion sensor. There’s no need for Stefan to visit the basement to check up, though: another Raspberry Pi shows this data on two additional LCD displays in the kitchen. If Stefan’s busy preparing food when he wants an update on Pumba’s environment, he simply presses a button on the kitchen display and gets an audible update.

A breath of fresh air: oxygen control

Temperature control wasn’t the only issue facing Stefan and his beloved tortoise. He also had to consider its oxygen supply. Whenever Stefan was at home, the fridge door would be opened regularly, refreshing the oxygen supply, but work and socialising often took him away from home. Stefan wasn’t prepared to risk the unthinkable and let the oxygen supply run out. Instead, he created an automatic door-opening system with a linear motor that opens and closes the refrigerator door at preset times and checks the door has been closed properly.

The (by now) very smart fridge automatically issues error messages, warnings, and notices, keeping Stefan abreast of any issues that might arise with his carapace-clad companion’s living arrangements. Should he need to, he can even remotely adjust the temperature and the timing of the fridge door opening, to allow more or less oxygen into the hibernation centre.

Emergency shutdown procedures

Stefan has spent many hours making the perfect hibernation environment for Pumba. The whole shebang is also safe from intruders and electricity outages. A Raspberry Zero W secures the whole setup. This has its own sensor in the refrigerator which measures the temperature and switches off the system completely when the threshold value has been reached, and sends a notification.

Stefan says, “Since I will probably never complete the work on this project, I am in the process of planning the next enhancements. Among other things I want to install in the near future are an ultrasonic vaporiser to regulate the air humidity and a scale for weight control.” He also plans to automate what the tortoise is fed and when.

Open door policy: keeping the tortoise safe

When no one’s at home, the oxygen controller kicks in, automatically opening the fridge door at preset times to refresh the air supply so the resident can breathe easily.

A range of sensors monitor the temperature in the fridge and the levels of oxygen available. LCD displays in the basement and kitchen show the current status of the fridge and when its door was last opened.

Oblivious to his owner’s Herculean efforts, Pumba luxuriates in a den of fresh leaves, precisely temperature-controlled and with ample fresh air and food.