Design of a Contactless Doorbell using Ultrasonic Sensors and Embedded Automation. International Journal of Research Publications in Engineering, Technology and Management (IJRPETM), [S. l.], v. 5, n. 4, p. 7101–7105, 2022. DOI: 10.15662/IJRPETM.2022.0504001. Disponível em: https://www.ijrpetm.com/index.php/IJRPETM/article/view/54. Acesso em: 12 feb. 2026.