An embedded system with a light-emitting diode (LED) and a phototransistor for soil nutrient measurement was developed (Fig. 1). The light from sample or reference cell was detected by a phototransistor. The detected signal was fed to the Atmega1284P microcontroller through signal conditioning circuit. The analog signal from phototransistor was converted into digital signal. The absorbance of the sample solution was calculated. A software programme was written for determination of the concentration of unknown species. The system was successfully used for determination of the concentration of Nitrogen and Potassium from the sample soil.

Fig. 1: Soil nutrient measurement system