MQTT Hardware Switch

Introduction

• Have an old Arduino Yún and a servo motor lying around?
• Need to automate a light switch etc. and don't want to deal with electrical installation?

We've got you covered!

I used this setup to automate my old, not so smart bathroom fan without having to fiddle around with the even older electrical installation of my apartment. All you need to do is to fit the Arduino and the servo motor into a nice looking box and upload this code. Before, make sure to copy the config template to config.h and fine-tune all values to fit your needs.

Et voilà! Enjoy turning your device on/off using MQTT commands and even integrate it in systems like Home Assistant with a minimum effort. 🎉

Optional: If you like, you can attach an additional hardware button and/or an LED to both control your device and also indicate its latest status.

🎬 Take a look at the doc directory for more images and videos of the device in action.

Documentation

MQTT messages

All topics are preceded by the base topic and a location tag, e.g. mqtt-switch/light-switch-bedroom.

All message consist of a JSON formatted string and will be retained by default.

Note the internal payload buffer limitation of 100 characters.

Direction	Topic	Description	Options/example
In	/command	Request to operate the switch.	{"switch":"top"} or {"pos":42} for testing
Out	/state	Current state of the switch.	{"actual":"neutral","latest":"top","trigger":"mqtt"}
Out	/avail	Availability indication (LWT).	{"state":"online","version":"Oct 30 2023 10:54:00"}

Example configuration for Home Assistant

mqtt:
  - switch:
      name: My fancy MQTT switch
      unique_id: 5054b2fb-bdc3-4d89-95c7-069dea94de6b
      device_class: switch
      availability_mode: all
      availability:
        - payload_available: online
          payload_not_available: offline
          topic: mqtt-switch/my_location_tag/avail
          value_template: "{{ value_json.state }}"
      state_topic: mqtt-switch/my_location_tag/state
      state_on: top
      state_off: bottom
      value_template: "{{ value_json.latest }}"
      command_topic: mqtt-switch/my_location_tag/command
      payload_on: '{"switch":"top"}'
      payload_off: '{"switch":"bottom"}'
      optimistic: false
      json_attributes_topic: mqtt-switch/my_location_tag/state

Development

A note on versioning

This sketch utilizes (of course!) Semantic Versioning. A macro constant GIT_VERSION is expected to be defined and will be printed out at program start-up. As there is no generalized solution - and that's a shame! - to fetch VCS version information at build time, providing this information depends on your own individual workflow. Check out git-describe-arduino for a sophisticated workaround.

However, the sketch will also run without any version information and automatically fall back to the compile date and time in that case.

Linting

python -m venv venv
source ./venv/bin/activate
pip install --upgrade cpplint

cpplint --recursive --extensions=ino,c,cpp,h,hpp ./