Creating a custom "device"

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Hi all.

I’ve been slowly getting into Home Assistant over the past year, but I’m still relatively new.

I’m wanting to know if there is a way to define arbitrary custom devices in Home Assistant. I’m thinking along the lines of the existing Generic Thermostat and Generic Hygrostat integrations.

But I essentially want to define my own integration with custom behavior, with a custom UI (“card” ?) that I would define.

Then, similar to the Generic Thermostat/Hygrostat, an instance can be added, with various individual devices and entities connected to the various connections that the integration requires, a card could just be added to the UI for that instance, and so on.

In other words, if I wanted to build the Generic Thermostat, from scratch, how would I go about that. (Not add an instance of the “Generic Thermostat” integration, but actually create my own, from scratch, that happened to behave in the same way, including the UI that comes with it, the setup, etc.).

Is this sort of thing possible?

I think I’m getting lost in the terminology, of what such a thing would be called, in the Home Assistant documentation. Or maybe my mindset about the whole thing is wrong.

I’m a software engineer by day, and my technical curiosity is getting the best of me. I just kind of want to know how it all works under the hood, what hooks are available for customization, etc.

I think this is a case of not seeing the forest for the trees.

I would love somebody to give me a 1000 foot overview about how Home Assistant works with regard to the above. Or please give me a link to any existing documentation on such. Or the source code to any existing project that is creating such a custom device/integration.

One of my actual use-cases will be a custom thermostat device. I’m going to have a dumb interface to my HVAC system (e.g., an ESP that is just passing the I/O through from HA, with some relays to toggle the heating/cooling/fan controls), as well as some discrete temperature sensors all around the house. I also have some dumb dehumidifiers connected to smart outlets that will toggle based on the humidity reading of same sensors. The thermostat/hygrostat control will be done by Home Assistant itself (there’s no physical thermostat device), with there just being a bunch of discrete sensors, and discrete outputs that it can toggle. Ideally this thing would be defined as a single cohesive virtual “device” in Home Assistant, that just ties in to all these other separate sensors and output devices, with its own UI that provides some asbtract input controls (like temperature set point), and shows current status information of the system.

I hope what I’m asking makes sense. If it’s not possible, or doesn’t make sense for whatever reason, please let me know. If there’s an alternate/similar approach that is more commonly used in HA, please let me know.

This is my first post here. Please forgive and missteps and let me know how I can improve my question for next time.

Thanks in advance.

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If you expect to release your code / take patches from others, then following the official documentation is probably the best plan.

However if you are just putting something together for yourself (don’t have any plans to open source it) then you might want to check out the MQTT integration.

MQTT is just a message broker, so in a nutshell to create a “switch” in home assistant you just have to handle a few JSON based messages to:

  • Be notified when HA starts up.
  • Register your switch (or switches).
  • Notify HA if the switch is externally changed.
  • Receive notification that someone (or an automation) has switched the switch in HA.

To be clear MQTT is a full integration (for many device types), but a basic switch will handle most real world use cases (it’s just the icons/filtering in HA will be incorrect).

So once you have the basics working (with switches) you can tinker with changing the device type, so that it shows up correctly in HA.

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No need to re-invent the wheel, you should be able to use jcwillox/hass-template-climate: :snowflake:Templatable Climate Device for Home Assistant, Supports Running Actions On Service Calls.

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I don’t quite understand the underlying problem. Why not use the Generic Thermostat?
You can always build your own custom cards on top of that.

1 Like
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The answer is no - you can’t create a device - from YAML or the UI. Even if you create a custom integration, the integration won’t be able to associate entities from another integration (generic thermostat) with its devices.

What you can do is use labels to group the entities together.