Integrating an Embedded System in a Microwave Moisture Meter

Abstract

The conversion of a PC- or laptop-controlled microwave moisture meter to a stand-alone meter hosting its own embedded system is discussed. The moisture meter measures the attenuation and phase shift of low power microwaves traversing the sample, from which the dielectric properties are calculated. The power level of the microwaves is similar to that of Wi-Fi. Therefore, the sample is unharmed and no heating occurs. The dielectric properties are then used for rapid, nondestructive determination of the moisture content in the grain or seed sample. The initial system consisted of the moisture meter, controlled via USB interface by an external laptop or PC. Though effective, the system lacked full portability and was susceptible to computer crashes and interruptions in communication between the meter and laptop. To improve the system, a microcontroller was selected in the design of an embedded system for the moisture meter. The microcontroller provides a graphical 144 x 32 pixel LCD and 16-button keypad to facilitate user interaction. The embedded system provides the following functionalities: user interface (input/output), event execution, process control, data acquisition and data storage. Testing showed that the moisture meter with the new embedded system maintained the performance and accuracy observed for the original meter with PC or laptop control. Results are included to show the similarity of measurements taken with the microwave meter (both versions) to measurements taken with a vector network analyzer. The integration of the embedded system with the microwave moisture meter provides a cost-effective, portable, and robust solution for microwave moisture sensing.