DEVELOPMENT OF A “SMART” WIRELESS SOIL MONITORING SENSOR PROTOTYPE USING RFID TECHNOLOGY

Abstract

Radio Frequency Identification (RFID) technology is commonly used for object or animal identification andtracking. In this article, we explore the feasibility of its use in a rapid solution to wireless real-time monitoring of soilproperties. A lab prototype system for wireless measurement of temperature was developed using a commercially available13.56-MHz RFID passive tag. Temperature is sensed by a thermometer Integrated Circuit (IC) that produces a Pulse WidthModulated (PWM) signal. An embedded Motorola 68HC11 microcontroller monitors this signal, produces averagedmeasurements, and sends them to the RFID tag or transponder unit, hence the smart feature of the sensor. A receivingunit also called the interrogator emits an electromagnetic field, which when detected by the passive RFID tag causes itto transmit temperature data stored in its memory to the interrogator. The latter detects these measurements and sends themto a data collection PC. The architecture of the sensor allows for the addition of other transducers without alteration of thetelemetry channel or significant changes to the sensor design. In benchmarking tests using a water bath over the course ofseveral days, measurement error over a range of 0 to 50.C showed a standard deviation of 0.5.C and a max error of 1.5.C.Measurements also showed a high correlation (greater than 99%) with those obtained using a thermocouple. The architectureof the developed wireless sensor prototype allows for additional soil transducers to be integrated into it without changes tothe sensor design. Potential applications for this sensor could be in the area of precision farming where soil properties suchas temperature might be monitored in a wireless manner. Although limitations in transmission range (less than one meter)would require proximity reading of the sensor, using existing equipment that regularly pass over the field as a mount for theinterrogator, such as center pivot booms or sprayers, would increase feasibility of this telemetry strategy.