TY - JOUR TI - Low energy wireless solution for soil moisture monitoring DO - https://doi.org/doi:10.7282/t3-apcm-3a53 PY - 2018 AB - With a growing world population placing ever increasing demands on agriculture and an increasing scarcity of water suitable for irrigation, there is a need for efficient irrigation techniques utilizing comprehensive knowledge of soil water content. While commercial solutions are available that provide the required of information, none were found that are low cost, low maintenance, and high durability. This thesis presents a sensor and data backhaul design that addresses these three key parameters with measurable results. The design uses a TPIP-K transmit-only wireless platform for remote reporting of the measurement data. Since soil moisture measurements need only to be taken at regular but not precise intervals and individual data points are not critical by themselves, no bidirectional communications are necessary, leaving communication channels open to measurement data only and allowing more sensors to be deployed for a given portion of wireless spectrum. Additionally, since the most energy consuming component is the wireless radio itself, the transmit-only design lends itself to long battery life because the radio is only active during the brief times data needs to be reported. A long battery life coupled with wireless communication means deployment is simple and unobtrusive to other agricultural procedures. The design of the moisture sensor itself is based on a variable value capacitor whose dielectric material is the water in the soil, making it simple and inexpensive to manufacture. The dielectric constants of air (εr = 1) and water (εr = 80) have a large enough difference that the concentration of water per unit volume in the soil will correspond to a specific capacitance value of the sensor. Making use of hardware features specific to the MSP430 microprocessor on the TPIP-K, precise and repeatable measurements can be made while maintaining low energy usage. Individual sensor calibration for a particular soil is achieved with measurements taken at low and new battery voltages, to account for battery aging, and approximately 25-30% and 100% field capacity, the point at which any additional water is drained from the soil by gravity and made unavailable to plants. Using bilinear interpolation based on the calibration data, the sensor can than report the volumetric water content of the soil between the calibration points to better than 3%, which is the range and detail of information most useful for agricultural irrigation purposes. The resulting sensor solution meets the set design goals of developing an inexpensive, low maintenance, and robust soil moisture sensor. KW - Electrical and Computer Engineering KW - Soil moisture--Measurement--Instruments LA - eng ER -