Hand-held soil moisture meter using polymer coated sensor

An appropriate proportion of water content in the soil is critical for plant growth [1]. The use of capacitive soil moisture sensor exploits the very property of soil that the dielectric value of soil varies with the amount of water content [2], [3]. Use of a capacitive sensor for soil moisture measurement provides some advantages such as better accuracy after soil-specific calibration, high sensitivity, flexibility in probe design, easy installation and cost-effectiveness. A copper cladded epoxy material, coated with a thin film of polymethyl methacrylate (PMMA) polymer, is an established procedure to fabricate the sensor [3], [4], which has been used here for soil moisture sensing. This paper describes the development of a rechargeable battery-operated hand-held meter for fieldwork by using this PMMA coated sensor along with a suitable signal conditioning circuit. The thermo-gravimetric method has been utilized to obtain the actual moisture content of soil [5] and calibrate it with respect to the voltage output of the meter. Moreover, with the moisture content, surrounding temperature and humidity are also useful atmospheric parameters used by weather stations [6]. For this, a DHT12 sensor has been integrated with this hand-held meter. IoT extension of measured data is implemented by a SIM900A GPRS/GSM modem to make the meter smart.