System Engineering and Deployment of Envirobat
Abstract- We report on a cost effective, portable urban air pollution monitoring device, Envirobat, based on commercially available gas sensors. In order to carry out air pollution monitoring over an extensively large area, the device integrates inexpensive solid state sensors, along with GSM Module which transmits measured data at multiple ground sites to a centralized server through GPRS. This device facilitates rapid dissemination of information on pollution levels at multiple ground sites simultaneously. The device has the capability to sense location, atmospheric pressure, temperature, humidity, CO2, CO, SO2, NO2, and O3. The device is validated through
calibration and deployment for indoor and outdoor sensing applications.
Microcontroller: The controller board is based on TI's MSP430F5435A microcontroller. It controls timings fo switching on/off of all sensors used in the device, processes the sensor output data and sends the sensor data to a server through a communication module (GSM). The board consists of the µController, powe management unit, sensor signal conditioning circuitry and provision for connecting sensor and communication boards. Fig.2a given below shows the Microcontrolle board design implemented on a PCB.
B. Calibration Methodology
General procedure followed for calibrating a gas sensor:
• Place the sensor under test in a closed chamber which will be filled by the gas to be detected.
• Set the concentration of the gas to a known value and fill the closed chamber with the gas.
• Record the output of the sensor continuously for "sometime" (depends on the flow rate of the gas and the chamber size) for uniform distribution of the gas in the chamber.
• Repeat the procedure for a different concentration of the gas.
• Plot the output of the sensor versus gas concentration.
• Obtain the relationship between sensor output and gas concentration.
• Compare it with the sensor's datasheet relation and obtain the offset between the datasheet's values and practical values.
• The gas concentration level is calculated from the measured EMF values at sensor electrodes for CO2 sensor. The actual EMF value decreases with increasing concentration of CO2.
Envirobat device is designed with easy user interface with display and keyboard for setting up various parameters during measurement. Also SD card interface makes the data available to user immediately. The user has option of creating his customized setting for transmitting data at appropriate intervals. This version of Envirobat demonstrates monitoring urban air pollutants and logging the acquired data for online access. There is a great flexibility for user to access the data from the device. The online GUI provides better user experience by visualizing the graphs.
The future version of Envirobat would include a touch screen to give user a better experience. A Zigbee module which will enable the networking between the devices so that devices can talk among themselves and there could be a single master device that communicates with server through TCP/IP protocol. The device settings of measurement periodicity, data upload periodicity could be controlled remotely from a computer terminal remotely. A Bluetooth module to facilitate the wireless data communication with hand held mobile devices is being worked on. A dedicated RTOS would be implemented on the device. The Envirobat module could be customized to suite various applications in air quality monitoring, locating the sources of pollution, personalized exposure to air pollution levels for health tracking etc.