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ggwave-arduino is an Arduino library for transferring data over sound for microcontrollers.
There is an iPhone & Android app for transmitting digital data via sound to an ESP32 development board with an Adafruit Electret microphone. The second breadboard (on the right) can also send data to the breadboard on the left.
The GitHub repo has an examples folder for sample circuits.
See a demonstration video below and more on GitHub.