A Low Cost Microcontroller-based Time Domain Reflectometer for Soil Moisture Measurement

Commercial soil moisture measurement devais based on time-domain reflectometry (TDR) are considerably expensive for daily practice by Indonesian farmer. In this paper, we present development of a low cost microcontroller based electronics soil moisture measurement system using TDR. We utilize the equivalent time sampling technique to enhance range of measurement frequency while the sigma delta modulation is used in implementation. Our sensor system is based on M-4 ARM Cortex microcontroller, working on a 100- KHz signal and virtual sampling resolution within 0.11 ns. The developed sensor system was able to reconstruct a typical TDR wave with reflection within several nanoseconds.