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Posts Tagged ‘Restful’

An exploration of connected devices

Introduction

Recently chez Architect has acquired a number of Internet of Things (IoT) devices, from a couple of Sonos wireless music speakers to more recently Hive, British Gas’s wireless home heater thermostat and boiler management system.  If you are familiar with Nest you get the idea.  More than 360,000 units have been installed across the UK alone and the rate of adoption appears to be increasing according to Nina Bhatia Managing Director of Centrica’s Connected Home Unit.

Hive has a number of features for controlling the heating and hot water in your home.  It comes with a fancy mobile app (I was impressed by the UX) and website for controlling your appliances remotely.  You can even set up a schedule for when devices are on or off.  The app allows you to adjust the temperature of your heating and also reports the current temperature in your home.  This article is not intended to be a review of Hive but an exploration of the APIs that these types of ecosystems provide.

After seeing the mobile app I realised that there must be an API to support it.  It is not widely advertised, or promoted by British Gas, but there are a number of blogs that make reference to it.  The original company that developed and then operated the Hive ecosystem was called AlertMe.  AlertMe was acquired by Centrica the parent of British Gas in 2015.  Slightly out of date documentation for the API can be found here http://www.smartofthehome.com/wp-content/uploads/2016/03/AlertMe-API-v6.1-Documentation.pdf.  This is the documentation for V6.1 of the API although the most current version is V6.5.  I’ve been unable to locate the latest documentation so here is a gentle appeal to Centrica to release it.

Hive supports a Restful JSON API, so I thought that I would write a simple application that would allow me to record the historic temperature within the home using the API.

Logging into Hive

The base URL for the Hive API is, https://api-prod.bgchprod.info:443/omnia.  In order to use this interface clients, users, need to be authenticated using the user-id and password setup for the device.  Once authenticated a 24-hour access token is provided that is used for all subsequent calls.  In order to experiment with the API I would recommend using the Postman App available for use with the Google Chrome browser.

To use the restful API a number of attributes need to be set in the HTTP header. For the initial client authentication call, [POST] https://api-prod.bgchprod.info:443/omnia/auth/sessions, three header attributes need to be set with the following values.

Content-Type: application/vnd.alertme.zoo-6.5+json
Accept: application/vnd.alertme.zoo-6.5+json
X-Omnia-Client: Hive Web Dashboard

Along with setting the header attributes, the POST request requires data to be passed in the HTTP body as a JSON object.  Below is an example of the request body.

{
    “sessions”: [{
        “username”: “xxxxxx”,
        “password”: “yyyyyy”,
        “caller”: “WEB”
    }]
}

Looking at the sessions structure it looks like the call can be used to establish multiple sessions in a single call but I have not tried this as I do not have access to multiple user accounts.

Once posted, the AlertMe API will respond by returning a JSON object in the HHTP body. Below is an example response

{
  “meta”: {},
  “links”: {},
  “linked”: {},
  “sessions”: [
    {
      “id”: “…”,
      “links”: {},
      “username”: “xxxxxxx”,
      “userId”: “vvvvvvv”,
      “extCustomerLevel”: 1,
      “latestSupportedApiVersion”: “6”,
      “sessionId”: “…”
    }
  ]
}

The session id is valid for 24 hours and is used in all subsequent API calls and is added as a fourth parameter to the HTTP header with the key X-Omnia-Access-Token.

Accessing Hive

Hive provides a number of function calls such as those for accessing the topology of your devices and discovering their status, in Hive terminology devices are called nodes.

The API function [GET] https://api-prod.bgchprod.info:443/omnia/nodes returns a JSON structure with all the details of the device nodes.  It is a bit of a kitchen sink function returning many details such as the thermostat settings and the schedule settings for each node.  When a node id is specified the results of a single node can be returned.  For instance by using [GET] https://api-prod.bgchprod.info:443/omnia/nodes/ the following structure is returned (collapsed).

{
  “meta”: {},
  “links”: {},
  “linked”: {},
  “nodes”: [
    {
      “id”: “ … ”,
      “href”: “…://api.prod.bgchprod.info:8443/omnia/nodes/”,
      “links”: {},
      “name”: “Thermostat”,
      “nodeType”: “…/node.class.thermostat.json#”,
      “parentNodeId”: “ … ”,
      “lastSeen”: 1485983701626,
      “createdOn”: 1481892545442,
      “userId”: “vvvvvvv”,
      “ownerId”: “vvvvvvv”,
      “features”: {
        “transient_mode_v1”: { …. },
        “temperature_sensor_v1”: {
          “temperature”: {
            “reportedValue”: 20.35,
            “displayValue”: 20.35,
            “reportReceivedTime”: 1485983701626,
            “reportChangedTime”: 1485983461820
          },
        “featureType”: { …. },
        },
        “on_off_device_v1”: { …. },
        “heating_thermostat_v1”: { …. },
        “thermostat_frost_protect_v1”: { …. }
      }
    }
  ]
}

By examining the nodes structure it is possible to determine the currently reported temperature of the thermostats in your home.  The time values are Unix timestamps representing seconds since 1st January 1970.

Observations

AlertMe appears to sample Hive devices on a two minute interval so there is no benefit in calling the API more frequently.  Sampling is also unreliable so updates to the sample values may be missed.  I have observed periods of up to eight minutes where the same value was reported before a revised sample update was successfully received.

The precision of the thermostat value is high to two decimal places which was a surprise.  I am not convinced the temperature reading is that accurate, but it was refreshing obtaining values to a fraction of a degree.

Hive Analytics

Now the real reason for why I was interested in accessing the AlertMe API for Hive was to build a picture of how temperature varies over time.

I wrote a simple Java application that logged in and polled the state of the devices in my house on a two minute basis outputting the results to a CSV file initially.  I used the GSON JSON parser which I found very straight forward and intuitive to use.

Below is a graph of temperature variation over twenty four hours.  The left axis is temperature in Celsius and the bottom axis is date and time.  You can see where the temperature dips when the heating was switched off over night and also during the day.

hive_temperature_chart

In my next blog I will describe how these values can be correlated to historical weather temperatures provided by the Met Office through their DataPoint API.

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