[Today’s temperatures are set to reach a whopping 38ºC/101ºF degrees in the UK, and none of us know what to do with ourselves. This doesn’t happen here and we have nothing prepared: we live in a society devoid of air conditioning, and we’re are unable to comprehend weather conditions more friendly than a slight chill and drizzle.

I can’t handle it. I have desk fan, but it’s in a cupboard somewhere, covered in dust and sadness. My local corner shop is already out of ice pops and ice cube trays. And anyway, I believe the tarmac on the road outside my house has melted and will suck down anything that dares step or drive on it.

I think I’m melting too. I feel sloshy, and, while I’m not 100% sure this is scientifically possible, I believe I may be partly barbequed. If someone presented me at a restaurant, I would probably be described as medium rare.

So yes, it’s hot. Very hot. It only makes sense that we share a Raspberry Pi project that fits with this theme: here’s an article from the latest issue of The MagPi magazine, out today, that shows you how Ishmael Vargas built his own smart fan for his home in hot and humid Chicago.

It’s a very clever idea, and one we wish we’d thought up ourselves before today’s sudden heatwave/opening of the Hell Mouth.

Enjoy — Alex]

When you need to keep your home cool during the summer months, a smart window fan could be just the thing.

Summer days, and nights, can be uncomfortably hot and humid in the Chicago area. As the sun goes down, the outside temperature drops, but homes may remain hot. This is where a window fan comes in useful, blowing cooler air into the house. Last summer, Ishmael Vargas was using a small window fan upstairs and, after turning it on in the afternoon, he found he had to get up in the middle of the night to turn it off. “That is when I thought there must be a better way to control this fan,” he recalls, “and I started putting this project together.”

Viewable via VNC on a smartphone, the program window features temperature data and control buttons.

As he was already using a DHT22 temperature and humidity sensor for another project, he opted to use that, connected to a Raspberry Pi Zero running a Python program, to monitor the room temperature. This is then compared with the external temperature; if the latter is cooler, the window fan is turned on via a smart WiFi power plug (TP-Link HS100) — a much simpler method than wiring the fan up to a relay.

Weather report

To keep things simple, Ishmael opted to source the outdoor temperature from Weather.com (The Weather Channel) using the pywapi Python library, rather than wiring up an external sensor. “The temperature provided by Weather.com as compared to the temperature in my car could differ by one or two degrees. This is close enough for this project,” he explains. “In other parts of the world or rural areas where they do not have as many weather stations, an outdoor sensor might be required.”

A smart WiFi socket is used to turn the window fan on and off.

One issue he discovered was that in the early morning, the fan could end up blowing warm air into the house. “Depending on the size of the fan, the size of the room, and the house materials, the inside temperature might never be as cool as outside,” he says. “For example, if the temperature outside is 65 °F (18°C), the temperature inside might only drop to 67 °F (19.5°C) through the night. As the temperature outside starts to climb, you want to keep the fan off.” This resulted in him adding an ‘inhibit’ mode to turn the fan off at 6am.

Remote control

Rather than having the fan program run automatically on bootup, Ishmael opted to start and control it manually via an Android smartphone. The latter runs the VNC Viewer app, enabling remote access to Raspberry Pi’s desktop, on which there is a shortcut to start the fan application; this then displays a Pygame window with temperature information and control buttons.

The DHT22 sensor is connected to power, ground, and GPIO 4 pins on a Raspberry Pi Zero — a 10kΩ resistor is recommended.

“The fan application has two buttons to change the [desired temperature] set-point up or down,” reveals Ishmael. “Also, the button on the upper right is to close the application and return to the desktop.” His aim is to have more than one project running on his Raspberry Pi, and have a desktop shortcut for each application.

While the original project used a single fan, he has since modified it to add another. “I have been reading that two fans are required for best performance,” he says. “One to blow in and another to blow out.”

This certainly is a cool project, in more than one way. If you’d like to have a go at building a similar system, you can read Ishmael’s Hackster guide and check out his GitHub repo for the code.

You should read The MagPi magazine

The latest edition of The MagPi magazine is out today, packed full of Raspberry Pi goodness. If you’re new to The MagPi magazine, welcome! As with all publications produced by Raspberry Pi Press, today’s new issue is available as a free download on The MagPi website, as well as in physical form from your local newsagent, the Raspberry Pi Store in Cambridge, or the Raspberry Pi Press online store.

Subscribers to The MagPi magazine get discounts and free stuff, and anyone purchasing any of our publications with actual currency will help fund the production of the magazine as well as the charitable work of the Raspberry Pi Foundation.