In the following I will show you how to process sensor data from an Arduino device with the Odysseus data stream management system.
Arduino as a sensor platform
The sensor we use in this Hand-on is a DHT11. The DHT11 is a low cost sensor capable to measure the temperature and the humidity of it’s surrounding. The DHT11 has actually four pins but uses only three pins: VCC, GND, and Data. We connect the power pins of the sensor to VCC and GND and connect the Data to pin 7 of the Arduino device.
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In the first line we include the DHT library. After that, we create an instance of the DHT class by setting the DHT pin to 7 and tell the library that we are using the DHT sensor version 11. In the setup method we start the serial connection and initialize the DHT. During the loop method we read the temperature and the humidity value and create a comma-separated string that is send over the serial connection. If everything is done, connect the Arduino to an USB port and compile and upload the program. That’s all from the hardware part, now we go over to Odysseus to perform the processing.
First Odysseus query
First fetch a fresh nightly build from the Odysseus website. Download the combined Odysseus Server and Studio bundle and unzip it. Before we start with our processing we need an additional feature to read data from the USB port. To do so, run the downloaded Odysseus Studio GUI by calling the “studio” executable. You can download new additional features using the “Install new feature” entry from the menu.
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Thus, Odysseus calculates the average of all temperature measurements of the last hour and outputs this average as shown in the next screenshot. Here, you also see one example of visualization using the Line Chart; many more are available using the context menu.
Advanced data stream processing
So fare, we have seen how Odysseus can be used to process measurements from an Arduino device in just a few lines of CQL code. Now we want to make some more advance processing including a pattern matching on the data and the transmission of processing results. To do so, we first have to install the “CEP and Pattern” feature using the “Install new feature” entry from the menu. This feature includes additional operator to perform so-called complex event processing. To use the new operators we will switch the query language to PQL. The PQL language allows connecting operators directly instead of describing a query in a declarative language like CQL. Also, we will now transfer processing results the same way we received the data from our Arduino. First, we create a new Odysseus Script like before, but select the PQL Basic. Thus, our first three lines change to:
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The SASE operator we use here takes three parameters, namely, the output schema, the type name of the output, and the query. The query parameter itself takes a pattern description written in the SASE pattern language.
Talking to the outside world
Right now, our query process the data from the Arduino device and finds situations when the temperature drops by more than 20% in one minute. So, we also want to get warnings when Odysseus detects such a situation. We could now use one of these fancy new social media stuff like Twitter, but I prefer the more old-school email. That’s why I use the SMTP transport handler to directly send the result of the SASE operator to an email address using the following operator in PQL:
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