Aaron Ardiri
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Internet of Things (IoT)

RIoT Secure AB


A great way to compare IoT hardware is to build similar solutions and give them a good test.

ControlEverything.com put together a Weather/Nav Kit (Kit-4) which I picked up while ordering the Photon and Electron micro-controllers from particle.io. I had previously build a temperature monitoring solution using an Arduino UNO and some DS18B20 temperature sensors, however due to the simplicity of the platform I commonly ran into minor issues. The particle.io Photon on paper seems to be quite robust; so what best way to find out by doing a field test with the unit and replicate the environment previously built and do a comparison.

The Kit-4 setup comes with four sensors; however for this project I was only interested in using three of them, namely SI7020-A20 (temperature and humidity), CPS120 (barometric pressure) and SI1132 (light sensor). The kit is simply to put together, simply connect the components together and the project then utilizes the I2C protocol for communication. Each sensor has a separate address and protocols however they are well documented - we will not be using the magneto sensor.

Of course; I could just as easily publish the values to the particle.io cloud - but in this specific case I only want to use the cloud for firmware distribution, my goal is to have the data sent to my own server for storage and analysis like was done previously with the Arduino UNO project. As expected; some great documentation exists for the Photon; specifically TCPClient.

The final hardware configuration, complete in a nice protective box looks like:

Viola; everything works as expected - basing my efforts on the previous build.

While doing the Arduino version; we were also forced to implement a watchdog timer to capture when the device becomes unresponsive or locks up in some way. A great example exists in the documentation and much like other platforms handle watchdog timer integration it is quite easy to implement within the sketch - effectively two lines of code required:

  • // configure the watchdog timer, is 15 seconds before check-in, reset
    ApplicationWatchdog wd(15000, System.reset);
    void loop()
      // pet the watchdog timer

Just another tribute to the particle.io platform - the fact they based so much on the familiarity of the Arduino platform means that developers who are familiar with it can migrate their solutions quickly and effortlessly. It literally took me a total of two hours to grab what I needed from the samples and migrate the existing code into the new project.

The end result - utilizing the highcharts.com graphing library:

Hooking it up to my existing cloud service and graphing system - we can see that after running for a few hours; everything seems to be working smoothly. It will be interesting to see how the software driven watchdog timer and system level network connectivity solution handles every day usage and deal with usage over prolonged periods of time.

I may need to re-consider where the weather station is placed, the light sensor picked up the outdoor light that remains on all night and the temperature seems to have picked up radiant heat from the unit itself (may need to expose the sensors more). It seems the LED lights interfere with the light readings as well so it may make sense to cover them - overall; the system reports data constistently and the is holding up well under the conditions.

The complete source code to the sketch (removed private elements) is here:

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