F. S. Yudha, Y. Yulkifli, A. Asrizal, and Y. Darvina, “Design of a Free Fall Motion Experiment Using E18-D80NK Proximity and HC-SR04 Ultrasonic Sensors: An IoT-Based Approach”, Department of Physics, Universitas Negeri Padang, vol. 2, no. 4, Dec. 2024.