Amazon Dot: Oops, Forgot Something

Just when I thought I could put this series of posts on the Amazon Dot and using it at my house aside for a while, I realized I forgot something last time <link>. I didn't show what a session with the example code I gave you last time looked like and what it was doing. So:

pi@housemonitor:~/src/alexa$ alexaIllustration.py
did the connect to AWSIoT
mqtt loop started
Alexa Handling started
mqtt connection to AWSIoT returned result: 0
Variable states:  79.1 1234.5 on
On Tick:  { "state" : { "reported": {"temp": "79", "barometer": "1235", "eastPatioLight": "on", "lastEntry": "isHere" } } }
Variable states:  79.1 1234.5 on
On Tick:  { "state" : { "reported": {"temp": "79", "barometer": "1235", "eastPatioLight": "on", "lastEntry": "isHere" } } }
{ u'eastPatioLight': u'off'}
got a delta
{ u'eastPatioLight': u'off'}
got command for east patio light:  off
Variable states:  79.1 1234.5 off
On Tick:  { "state" : { "reported": {"temp": "79", "barometer": "1235", "eastPatioLight": "off", "lastEntry": "isHere" } } }
{ u'eastPatioLight': u'off'}
found left over desire at eastPatioLight
sending: { "state" : { "desired": {"eastPatioLight": null} } }
Variable states:  79.1 1234.5 off
On Tick:  { "state" : { "reported": {"temp": "79", "barometer": "1235", "eastPatioLight": "off", "lastEntry": "isHere" } } }

Above is a session where I start the process and give it a command. The first thing that happens is that a connection to AWSIot is established. This is really a normal ol' mqtt connect, and then an mqtt loop is started. This is an asynchronous loop that will return control back to the code so other things can be done.

When the connection calls back the code subscribes to the two topics and prints the connection message, "mqtt connection to AWSIoT returned result: 0." This means that we are all set up and ready to receive messages from Amazon. I printed the starting state of the variables next and the interesting one is the eastPatioLight which I initialized to 'on'.

The 'On Tick' messages are the reports we're sending up to Amazon. I have this set up for every ten seconds so we don't have to wait long to see something. Scan down a bit and look for, "got a delta," because that is the point where a command came in from Amazon. In this case it's a command to turn the eastPatioLight off.

The next 'On Tick' message says that the light is now 'off' and should change the Shadow document to reflect that. Then, the code sees another delta message and checks to see if it has already been satisfied and decides that it's simply a leftover desire and sends back a JSON string:

{ "desired": {"eastPatioLight": null} } }

This will remove the desired entry from the Shadow and therefore, the delta message will stop.

And it's done. The variable has been changed to 'off' and if you had code there to turn off your lights, so would be the light.

After you work with the interaction a bit, it will all make sense and will be MUCH easier to modify for your particular use and add stuff to.

Have fun.