This paper describes a system for soil moisture measurement based on a waveguide spectrometer. The system fundamental components are a waveguide and an electronic circuit, generating the electromagnetic waves and elaborating data, driven by a microcontroller. Therefore, acquisition of measurements and samples were conducted on real soil, and these data were used to obtain a good calibration model. Calibration coefficients were used to implement the moisture calculation directly in the microcontroller, obtaining a non-invasive and stand-alone system. The architecture prove the capability of electromagnetic waves to perform accurate and fast silty clay loam moisture assessments on a real environment.