Good day, My graduation assignment is a prototype of a localization module to be used inside a greenhouse. The method that I am using is Time Difference of Arrival. The two signals that are part of it are radio frequency via an XBee and ultrasonic signal via a HC-SR04. My goal is to use four beacons and one tag to establish the localization prototype. Currently, I am facing a problem that I cannot solve which is letting the HC-SR04 communicate with one another. The goal is let one(tag) HC-SR04 work( https://www.hqew.net/news/news-33872https://www.hqew.net/news/news-33872 ) as a transmitter and the other (beacons) as receivers. Therefore, I am able to send an ultrasound signal and time the duration thereof. Furthermore, I am able to calculate the difference between the XBee and the Ultrasound units. Once, this is executed the distance can be obtained between I hope this provides clarity of what I am doing, and I kindly ask you for support. Thank you in advance for any help you are able to provide. BR, Erino N.B. Is it possible for the HC-SR04 to work as a receiver? If not, what are the possibilities to let an ultrasound module work as a receiver or transmitter?