Wireless Sensor Network

Introduction

This repository contains all files needed to reproduce the Wireless Sensor Network (WSN) used for the Data-Driven Building Retrofit Research of the A/S Chair. The WSN is intended to be deployed in residential buildings to collect sensor data for building model calibration. The microcontroller boards are based on the Arduino framework. For wireless communication, XBee radio modules are used.

See the Wiki for documentation, instructions, and other resources.

Structure of the WSN

Sensor-Kit: (from left to right) two sensor nodes, gateway and router node

The WSN has a modular structure. The main components are the following: * Gateway * Router Node * Sensor Node

On the sensor node, the sensor readings are performed and the data is relayed over router nodes to the gateway using the XBee network. The gateway forwards the data over cellular network to a web server, where the data is stored in a MySQL database. It is also possible to use a sensor node as data logger without any radio communication.

Sensor Node

Sensor nodes consist of two parts: the main module and the sensor module. The sensor module interfaces the actual sensor(s). It reads out the sensor reading and transmits the result via the serial bus in a unified format to the main module. The main module interfaces the sensor module, radio transceiver, and the battery. It forwards the readings from the sensor module to the gateway. Both, the main module and the sensor module, can be programmed using the Arduino IDE.

Main Module

The main module is the same on all sensor nodes. It entails the following: * Microcontroller (ATmega328p) * Real-time clock (DS3231) * Battery (2000mAh LiPo) * SD-card socket * XBee radio module (XB24CZ7WIT-004) * Slide switch and LEDs for debugging * Power jack for external power * Connectors to sensor module

The tasks of the main module are: * Scheduling (RTC or interrupt from sensor module) * Interfacing the sensor module * Interfacing XBee * Interfacing SD-card * Reading the charge state of the battery * Switching between normal operation and debugging mode

Sensor Module

The sensor module interfaces the actual sensor(s). Each sensor or sensor configuration needs its own sensor module design. The following sensor modules are available: * Temperature and Humidity (SHT31) * Luminosity (TSL2561) * Pulse * CO2 (S8) * Heat Flux (gSKIN XO) * Dual Temperature (DS18B20) * Prototyping

There are two kinds of sensor modules: sensor modules for periodic measurements (fixed time interval) and sensor modules for event based measurements (interrupt driven). On the first power-up of the main module, the type of the sensor module is requested, in order to set the mode to periodic measurements or event based measurements. For periodic measurements, the main module is woken up by the RTC on the main module. It then turns on the power to the sensor module. After power-up of the sensor module, it reads out the sensor(s) and transmits the readings over the serial bus. Then the power to the sensor module is cut by the main module and the data is written to the SD-card and/or sent to the gateway via radio. For event based measurements the sensor module is always powered on. The main module is woken up by an interrupt signal from the sensor module instead of the RTC. The data transfer is the same as for the periodic measurements.

Gateway

The gateway receives the data from the sensor nodes and relays the data to a web server via 3G cellular network. The gateway consists of Adafruit Feather 32u4 FONA and a XBee radio-module. The Adafruit Feather 32u4 FONA can be programmed using the Arduino framework. The gateway is powered via USB power supply and needs to be always powered on.

Router Node

A router node consists of XBee-radio module and SparkFun XBee Explorer Regulated Board. The router node is powered by a wall adapter power supply. It always needs to be powered on.

Publications

• Wireless sensor network for estimating building performance
• An easily-deployable wireless sensor network for building energy performance assessment

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