Design, fabrication and calibration of a low cost smart sap flow measuring system based on ATmega 328/P microcontroller.

Abstract

A microcontroller driven sap flow measuring system was designed and constructed for automating the measurement and recording of sap flow in plants. The system comprise of an ATmega 328/P microcontroller which forms the heart of the controlling circuit, real time clock for providing timestamps to the measured data and an external secure digital card for storing measured sap flow data. The system uses a thermal dissipation sap flow sensor for measuring sap flow and this was fabricated using hypodermic needles and type-T thermocouples, making the fabrication procedure inexpensive. The total cost for constructing the sap flow system was US $72.64 excluding labor costs. The system was calibrated and tested over a fortnight period on a fountain tree. The calibration graph indicated a linear relationship between the actual sap flow rate measured using the dynagage sap flow sensor and the sap flow rate measured using the thermal dissipation sap flow sensor, with a good coefficient of determination value of 0.8211. The calibration graph produced a calibration multiplier of 18.542 with an offset value of 124.4 g/h. The system produced satisfactory results with a good storage of the measured data over the duration of the experiment. It was concluded that the smart sap flow measuring system is suitable for measuring sap flow rate in trees.