Hello!

I'm currently working on automating my house by connecting everything to my Mac HomeKit system.

The next piece of equipment I'm tackling is my air exchange unit (HRV). Right now, I’ve got it partially automated by connecting a standard 10-amp Wi-Fi-controllable switch to it. I also turned the mechanical humidity controller to its maximum setting. Now, whenever I turn on the Wi-Fi switch using my phone, it powers up the HRV. Step 1 is complete.

Here’s where I need help:

Without the Wi-Fi switch, the HRV can be started from the bathroom using a simple push-button on the wall. This button is connected to the HRV via two wires. When pressed, the HRV runs for 20 minutes and then stops. While it’s running, a green light on the button turns on.

I’d like to retain the same functionality when pressing the button. My plan is to connect a small Wi-Fi-enabled device (like an Arduino or Raspberry Pi) near the HRV. I’d connect the two wires from the button to this device. When the button in the bathroom is pressed, it would close the circuit on the device, and the device would wirelessly trigger the HRV to turn on through HomeKit. Both the HRV and this Wi-Fi device would be connected to HomeKit.

My Questions:

1. What hardware do I need for this setup? For example, if I use an Arduino UNO R4 WiFi, can I connect the two wires from the switch directly to the board without using a relay? The wires are about 50 feet long.
2. Can I replicate the functionality of the LED indicator that stays lit while the HRV is running?
3. Any advice or schematics for the hardware setup would be greatly appreciated. I’m comfortable with coding but need guidance on the hardware side.

Thanks!

 

Welcome to AAC.

There are a number of approaches you could take in solving this problem. I am going to suggest one that—while not the simplest on the front end—will provide a platform for future growth.

Some things to consider:

HomeKit uses Matter, a Matter compliant solution will make things much simpler since nothing will be hidden from it (that is, no "back door" operations are required and the Home app will properly reflect the status of the device(s)).

In the general case, sticking to the most universal solution for the DIY aspects of your Home Automation build will pay large benefits in the future s you add new devices.

As an example, my own HA infrastructure uses HomeKit, but is also uses devices connected via Philips Hue, Samsung Smartthings, Shelly, eWelink (Sonoff), Tuya, Wemo (Belkin), and VeSync—as well as services like Twilio (SMS. telephony), and open source data for weather and other information. Additionally, it integrates ESPHome and BTHome which are extremely powerful.

The main organizing principle of all of it is Home Assistant. Even though the user-facing front end is Apple Home, with Siri and the mobile app as the interface, the core of the system is HA. This is because HA has a very effective HomeKit bridge capability that allows exposing all of the devices I connect to it as natively controllable devices to HomeKit.

HA also has a very customizable mobile app and a good voice assistant which can be used alongside Apple Home if desired. HA is open source, completely free, and very widely supported. The original developers of HA now also offer a cloud service that will provide safe off-premises access to your HA installation, as well as backup capability.

So, form a software perspective, using HA as the core of your infrastructure is a really big win. And, it can be used seamlessly with Node-RED, allowing you to create HomeKit-native virtual devices, for example—but also a lot more (this can wait until you have you HA bearings, but it is a great option as you know more).

On the hardware side I unreservedly recommend Shelly*. Smooth integration with HA, reasonable cost, great build quality and amazing capabilities make it my top choice. Shelly is 100% on board with DIY and open source applications, actively supporting both HA integration and reflashing of their ESPx-based device with alternative firmware (something I haven't felt the need to do, but can be very useful if you choose something like ESPHome for DIY-built devices).
*as I am writing this, Shelly has a Black Friday promotion running which is the target of the URL above, if it is broken go here instead.

So, with HA and the appropriate Shelly device, you will not only have an excellent solution but a platform for any future growth. HA offers a way to integrate nearly anything interesting into your home automation infrastructure, and Shelly will give you a really nice range of hardware at high value prices.

Yes, HA has a learning curve, but you don't have to use all of it, and it can be extended incrementally. It will happily run on a Raspberry Pi, or any other SBC that can run Linux. There is a one-shot solution distribution called Home Assistant OS, which is a painless way to get everything running and is actively developed.

You can find a tutorial here, and it is typical of the very extensive documentation on just about every aspect of HA, its installation, configuration, and maintenance.

I very strongly recommend HA and Shelly, without reservation. If you have questions, of course you can post them here. HA also has a very active user community, so information on just about everything is very easy to find. Good luck, and I hope you find this approach attractive—it is a lot of fun to have so much capacity at your fingertips.

 

I struggle to imagine the benefit of replacing a correctly operating hard-wired connected button portion of a system with a WiFi link to do exactly the same thing. All of that connecing hardware will need to reside someplace.

 

I struggle to imagine the benefit of replacing a correctly operating hard-wired connected button portion of a system with a WiFi link to do exactly the same thing. All of that connecing hardware will need to reside someplace.

Limited imagination is a restraint on fun.
Me.

"Imagination is more important than knowledge, knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. It is, strictly speaking, a real factor in scientific research.”
Albert Einstein.

 

I have discovered over the years that it is entirely possible to imagine some really poor choices and ideas. I have observed others doing it as well. Reality can be rather brutal.