C. Dan Michael A, M. Charito M, A. Marmelo V., and S. Myra S, “Nullpest: a mobile application of agricultural pest locator using sonar sensor set-up”, IJET, vol. 7, no. 3.29, pp. 107–109, Aug. 2018, doi: 10.14419/ijet.v7i3.29.18535.