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He wants to send a byte of data.I can whisper to somebody who is only 25m away. Why do you need ultrasonics?
you certainly must have good ears if you can understand a whisper 25m away.
The whisper or the ultrasonic?maybe it is possible but it requires a lot of power for 25m range since it is very low frequencies
So for your purpose you don't need the light feedback circuit and the distance calculation. You just need the ultrasonic transmitter and receiver.I've found this one so far. It suggests using an ultrasonic send to a remote receiver. The receiver then pulses a light back to the sender. Distance measurement uses speed of sound and speed of light.
https://www.electro-tech-online.com/custompdfs/2010/12/ESP15_USp-1.pdf