There are dozens of these in existence. Some you may have used without knowing even, eg: https://www.engadget.com/2014-06-27-chromecast-ultrasonic-pa...
This is also how modems used to work, for the young'uns who do not know this.
This is also how modems used to work, for the young'uns who do not know this.
they still do, but they used to too.
1200 bps V.23 and Bell 202 are still in use in radio telemetry applications.
I use it to connect to a Windows machine that runs a large piece of machinery in a remote location.
My dry cleaner's credit card reader, too.
Uh, don't try and find this if you're going to use it to pollute the spectrum i am licensed for.