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Sensor Network History 3 – Third Iteration (current)

A project log for SENSEation

Modular sensing platform for research

mario-freiMario Frei 09/20/2018 at 17:540 Comments

By now, I got a bit of experience with deploying and operating sensor networks. The major improvements of this iteration are:

The following aspects remain unchanged from the last iteration:

The sensor nodes of the third iteration of the sensor network were split into two modules. The main module takes care or power supply and communication, and the sensor module interfaces the sensors and relays the sensor readings to the main modules. This allows separating the hardware and software development of the sensors from the rest of the sensor network.

The main module features an ATmega328p, an Xbee, SD-card, RTC, LiPo-battery, power jack for mains adapters and connectors to the sensor module. The measurement interval is set on the main module. When it is time to take a measurement, the RTC will trigger an interrupt on the microcontroller, and the power to the sensor module is enabled. The sensor module then reads out the sensor and sends the data via serial to the main module. Then the power to the sensor board is again disabled. The measurement data is sent to the Gateway via Xbee. The measurement data can in addition stored on the SD-card of the main module with a time stamp from the RTC.

The sensor modules generally consist of an Atmega328p, connectors to the main board and various sensors. When the power to the sensor module is turned on, it reads out the sensor data and puts the data in a unified payload format for convenient data transmission and insertion into the database. Available sensor nodes are:

Router nodes still consist of an Xbee on a SparkFun XBee Explorer board powered by a mains adapter.

For the gateway, I chose an Adafruit Feather 32u4 Fona. It is Arduino compatible and features a GSM modem. The XBee is connected to the Feather Fona via a simple custom PCB. The image below shows from left to right two sensor modules, a gateway, and a router node.

With some support from students during development and production, we manufactured eight sensor kits with 18 sensor nodes each, plus some spare ones, about 150 in total. The sensor kits were deployed in eight single-family buildings. Some of the results can be found here: https://www.sciencedirect.com/science/article/pii/S1876610217329077

The installation of a sensor node took on average seven minutes per node. This is a huge improvement compared to 45 minutes with the previous version. The batteries lasted 10-12 month for most nodes. Exceptions were the nodes for windows opening times. The nodes for pulse counting and CO2 were powered by a mains adapter. During the deployment, I observed some issues with the gateway, leading to some data loss.

In summary

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