Wednesday, June 17, 2015

OK, Fine, I'll take a look at MQTT

A number of my readers have mentioned mqtt as a great tool for the kind of thing I'm doing around the house. A couple of them have pointed out that what I'm doing could be done much easier using mqtt and even sent me web sites to look at.

Naturally, I resisted. That's sort of the way I am, but also, the various web sites out there make it look so complex that I just didn't want to try and deal with it. Another stinking process with an API and things I had to learn to use it ... gag!

Then Glenn sent me a link to an Arduino implementation of publishing data to an mqtt server <link> and things clicked into place. What happened was the Arduino was too small and slow for fancy implementations, it had to fit in a couple of K and run on a 16MHz machine, so it was as simple as it could be. That got me to thinking --- there's really no protocol, you build it yourself, There's no registration, special language, ... none of the stuff that drives me nuts. You just use it.

Fine, I've eaten my words before, so I gave it a shot. AWESOME set of tools. This thing is going to be the center piece of a major update to my house control system.

OK, Glen, Brant, others too many to itemize, go ahead ... scream, "I told you so, but you wouldn't listen." I deserve it.

The way I started was to install the mqtt client software on my weather station Pi. I put a few lines in the python code to import, initialize an object and then a single line to send the data to a public mqtt server. Yes, that's literally all there was to publishing data, one single line of actual code.

Then I used the one of the tools to see if it actually got there and I could read it back.

pi@deserthome:~/src/other-things$ mosquitto_sub -h "" -t "Desert-Home/#" -v
Desert-Home/Weather/String {"sensorId":{"SID":"92","t":"1434572606"},"channel":{"CH":"A","t":"1434572606"},"messageCaught":{"MC":"0","t":"1434572606"},"battLevel":{"BAT":"7","t":"1434572606"},"windSpeed":{"WS":"4.0","t":"1434572606"},"windDirection":{"WD":"SSE","t":"1434572587"},"temperature":{"T":"111.7","t":"1434572606"},"humidity":{"H":"11","t":"1434572606"},"rainCounter":{"RC":"445","t":"1434572587"}}

Desert-Home/Weather/String {"sensorId":{"SID":"92","t":"1434572606"},"channel":{"CH":"A","t":"1434572606"},"messageCaught":{"MC":"0","t":"1434572606"},"battLevel":{"BAT":"7","t":"1434572606"},"windSpeed":{"WS":"4.0","t":"1434572606"},"windDirection":{"WD":"SSE","t":"1434572587"},"temperature":{"T":"111.7","t":"1434572606"},"humidity":{"H":"11","t":"1434572606"},"rainCounter":{"RC":"445","t":"1434572587"}}

Desert-Home/Weather/String {"sensorId":{"SID":"92","t":"1434572623"},"channel":{"CH":"A","t":"1434572623"},"messageCaught":{"MC":"0","t":"1434572623"},"battLevel":{"BAT":"7","t":"1434572623"},"windSpeed":{"WS":"2.5","t":"1434572623"},"windDirection":{"WD":"SSW","t":"1434572623"},"temperature":{"T":"111.7","t":"1434572606"},"humidity":{"H":"11","t":"1434572606"},"rainCounter":{"RC":"445","t":"1434572623"}}

If you've been following the weather station posts, these lines will look really familiar. The tool mosqitto_sub is a test subscriber that took the public server I used, '', and looked for the published data keyed under 'Desert-Home/Weather/String' and printed it to the console of the Pi. So, what was happening was that my weather station Pi was reading the data from a radio and sending it over the internet to a server. Then on a different Pi, I was reading the data back as it came in from the server I subscribed to. Three machines involved working over the internet and all I had to do was write one line of actual code to do it.

To try it out, install the mqtt client software for python and the command line tool I used above. No, I didn't misspell it, there really are two 't's in there.

 sudo apt-get install mosquitto mosquitto-clients
 sudo pip install paho-mqtt

This will actually install the mqtt broker and start it up, but you can stop it by the command:

sudo /etc/init.d/mosquitto stop

Then, in some code somewhere, put the lines:

import paho.mqtt.client as mqtt

mqttc = mqtt.Client()
mqttc.connect("", 1883, 60)

To create the object, initialize it and start it up. Then the single line somewhere you are logging or recording something like this:


The string "Desert-Home/Weather/String" is called a 'topic'. This is a hierarchical set of keys that you construct for your own purposes. I chose "Desert-Home" for obvious reasons, then "Weather" because it's for the weather station, then "String" because I was publishing the JSON string produced by my code that reads the AcuRite 5n1 weather head. I may create another item "OutsideTemperature" to hold the latest outside reading from the fence post sensor in which case it would be:


Then to get the data back as it is published to the server, use a line like:

mosquitto_sub -h "" -t "Whatever/you/decided" -v

Slick isn't it. There's no mystery here, no special stuff you have to learn, it's all totally up to you how you use it. To make it more versatile, the '#' and '+' characters have special meaning that can help you debug and select things. Check the various sites out there for the usage of those symbols.

There's a ba-jillion web sites out there that talk about mqtt, so I'm not going to recap the light-weight, short transaction, fail safe blather that they cover ad nauseum, instead over the next few weeks, I'm going to convert my house monitor and control system to actually use it and try to show you how to follow my footsteps improving and changing it to suit your particular needs. I'm sure I'm going to mess it up and have to redo things a couple of hundred times, but this should, at least, be good for a laugh.

During this process I'm going to visit my sensor devices and update the code on them to my latest experience level and implement several changes to them as well. JSON strings as data output and input so I can get rid of parsers, that kind of stuff. I'll gateway the devices from the XBee network to messages that will be published to mqtt and caught by whatever needs to handle the data. I don't know what I'm going to do with the Iris devices yet, but something will come to me.

Stay tuned.


  1. Ahem. I don't want to say I told you so, but.
    Hee Hee Hee.
    I can hardly wait to see the results.

    1. I'm working on it now, but it's going to be a pain converting. It'll be much easier to update things in the future, but I've stuck so much stuff around the house that moving over will suck.

  2. Have a look at MQTT Lens:

    1. It's in my browser now. Nice little tool for debugging or monitoring what's going on. I may have to hunt down the source and ...