Near Intersection of I-35 & I-90 Southern Mn. | Your request is certainly possible. One needs to be concerned about safety when using approaches to allow a Phone App to turn ON/OFF devices remotely. Your request of being able to turn ON/OFF a fan seems quite safe. Using such a system to turn ON an auger remotely offsite might not be safe as there is always the possibility of turning it on in error with dangerous results. "Butt dialing" by accident happens from time to time and we wouldn't want it to lead to injury.
I use an arrangement that uses low cost microcontroller/relay boards. A picture of one with 6 relays is shown below. The one shown is for an old shed with two door openers. I use them with a phone app to be able to remotely control the door openers on an old shed and a door opener and lights on my farm shop. My arrangement uses the WiFi capability in my phone and the relay board directly called a Soft Access Point. This means that the internet is not necessary nor is it used. This is necessary in my situation since I do not have internet access at those buildings. In my situation not using the internet is not really a downside since I only need to operate the openers and lights when I am reasonably close to those buildings.
I could use the same equipment and change the program so that it does use the internet as the communication link between the phone and the microcontroller relay board. If I did such, I would be able to work with my door openers/lights anywhere I had internet access. For me this is not necessary nor desirable. This type of arrangement should be possible to allow you to control a fan.
In my case, I wired the relays on the board to behave as a second 3 button UP/DOWN/STOP switch. This means I can use either the original 3 button switch or the phone to start/stop the door opener functions. In the shop implementation, I use a four relay board. Three of the relays mimic the UP/DOWN/STOP functions of the opener and the fourth triggers a contactor that can handle the electrical load of my shop lights. This means I can control the lights either with a push button on the wall in the shop or by the button on the phone app. I can start/stop an action with any combination. I find this very handy when I quit harvesting for the night. As I return home, I can use the phone to open my large shop door and turn on the lights.
I use an ESP 32 microcontroller/relay board such as the one shown below. The one shown is for the old shed that has two openers. It needs 3 relays for each opener. I have another for the shop with only 4 relays which is sufficient for one opener and the lights. I use a website called RemoteXY to create the sketch or program that gets loaded on the microcontroller. This website allows me to assemble a screen layout that suits the situation. The website allows me to "build the program" without understanding all the inner workings. This sketch is then loaded onto the microcontroller which is constantly powered and wired into the door openers and light contactor. A RemoteXY app is installed on the phone which when active retrieves the screen layout from the microcontroller and presents it on the phone for use.
This really works very well but is probably not for everyone as it is a bit of a DIY kind of thing. Strange as it may seem, I get satisfaction in setting these things up and seeing them work. Some like these are even quite useful.
There are various devices that make use of the internet and a phone to control things that might be more attractive to those who have "better things to do".
The pics below show the typical microcontroller relay board that I use with my old shed with two door openers, an enclosure outside by my shed door and a screen shot of my phone for my shop. The final screen shot shows a simple example that would work with a single relay to control a single contactor for your fan.
Edited by tedbear 7/29/2026 06:42
 (ShedESP32 (full).jpg)
 (Shed Box 75 (full).jpg)
 (Shop 30 (full).jpg)
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 ShedESP32 (full).jpg (99KB - 9 downloads)
Shed Box 75 (full).jpg (99KB - 13 downloads)
Shop 30 (full).jpg (18KB - 9 downloads)
BlockControlOff (full).jpg (164KB - 16 downloads)
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Looking for a relay that can be turned on through wifi
