Amazon launched Echo in the UK today – it’s been a long wait! My pre-ordered Echo arrived this morning and my first priority was to get it (her?) to control my home lighting. As I’ve previously written about, my LightwaveRF lights are currently managed by a custom set of scripts communicating within the house using MQTT pub-sub. This means that Amazon Echo (or Alexa, as I’ll refer to it/her from now on) doesn’t know how to interface with them like she does with Philips Hue, for example.
Luckily Amazon has made available its Smart Home Skill API which allows individuals and home automation vendors to provide “skill adapters” for the various home automation “skills” Alexa already has. This means it is possible to say “Alexa, turn on the bedroom light” and have Alexa use whatever underlying system and technology you have to execute the command. This is preferable to defining a new custom skill because it avoids the need to use a skill trigger word (e.g. “Alexa, turn on the bedroom light using LightwaveRF”). AWS Lambda is used to provide the concrete implementation for the abstract actions.
In my case the skill adapter will make a HTTPS call to an Octoblu trigger node passing details of the required action (essentially just a MQTT message with the topic being the light to control and the message body being the action (on or off)). The Octoblu flow then messes about a bit with the JSON structure before passing the message to an existing Meshblu device that connects my home MQTT world with Octoblu. In reality I’m using Octoblu and Meshblu here as firewall-bridging plumbing to get a MQTT message from the Lambda function into my home environment.
Having signed up for my Amazon developer account I followed Amazon’s steps to create a Smart Home Skill. This started by creating a new skill (of type “Smart Home Skill API”) in the Alexa Skills Kit section of the Amazon Developer Console – I chose to name this skill “James’s Lights”.
To provide the actual implementation I created a Python 2.7 Lambda function named “JamesLightsSkillAdapter” in AWS (using the eu-west-1 (Ireland) region to co-locate with the Alexa voice service for the UK) based on the alexa-smart-home-skill-adapter blueprint. I based the code on the template provided in the “steps to create” page above. For the role I selected “Create new role from template(s)”.
The code handles two separate types of message from the Alexa service:
- Device discovery – this is an action initiated by the end user from the Alexa app (or by voice) to get an inventory of devices that Alexa can control. In the Lambda function this is implemented by returning a big blob of JSON with an entry for each device. The “friendlyName” item being the words Alexa will recognise to control the device. I’m using the additionalApplianceDetails item to record the MQTT topic that will be used to control this device. My initial prototype implementation hard-codes the entire inventory in the Lambda function – clearly not a long term solution!
- TurnOnRequest and TurnOffRequest commands – these are issued by the Alexa service when Alexa is asked to turn a device on or off and the device is recognised as one in the inventory. The Lambda function is called with the relevant JSON blob and therefore my code can pull out the previously configured MQTT topic and send that as part of a HTTPS POST to the Octoblu trigger mentioned above.
I tested the Lambda function using the “Alexa Smart Home – Control” sample event template, manually crafting the JSON messages to match the ones the Alexa service will be sending. After testing it’s important to make sure to enable the Alexa trigger for the Lambda function.
Back in the Developer Portal I configured the skill to use an endpoint in AWS Europe using the Lambda ARN created above. As this will be a private skill adapter I didn’t really need account linking (this is how a regular user would link their Echo with, for example, their Philips Hue account) but the console wouldn’t let me proceed without setting it up. Therefore I followed this great blog post’s instructions on how to use Amazon itself as the linked account.
Having saved all the skill configuration and enabling testing I then used the Alexa app on my iPad to add this newly created skill (in the “Your skills” section) and logged in with my Amazon account as the account linking step. From there is was a simple matter of letting the app and Alexa discover the devices and then Alexa was good to go.
I can now say to Alexa: “Alexa, turn the lounge light on” and a second or so later it’ll come on and Alexa will say “OK”. What happens under the hood is more interesting though:
- The Alexa cloud service processes the message, figuring out its a smart home control command
- The Alexa service looks through my discovered device list and identifies the “lounge light” is one that is controlled via this skill adapter.
- The Alexa service makes a call the my AWS Lambda function with a JSON message including the configuration for the requested light as well as the “TurnOnRequest” command.
- My Lambda function makes a HTTPS POST call to the Octoblu trigger with a MQTT-like message including the topic string for the requested light and the “on” message.
- The Ocotblu flow forwards this message via Meshblu to a simple Meshblu connector I have running at home.
- My Meshblue connector publishes the messaage to my local MQTT broker.
- The LightwaveRF script also running at home and subscribed to “Light/#” messages picks up the message and looks up the room/device codes which it then send via UDP to the LightwaveRF bridge.
- The LightwaveRF bridge sends the appropriate 433MHz transmission which is picked up by the paired light fitting and the power is switch on.
As this is all highly customized to me I’ll be leaving the app in its testing state, not putting it forward for certification (which would certainly fail!) and publication.
Right now the implementation hard-codes my device list as well as the URL of my Octoblu trigger. I’d like to, at the very least, make the device list dynamically generated from the equivalent configuration inside my home MQTT environment.
What I’ve built here is basically an Alexa to MQTT bridge. This means I’m not limited to 1-to-1 control of individual lights. With the right MQTT messages in the device discovery JSON blob I could also control groups of lights, timed sequences, or anything else I care to code up.