They used the webaudio API to send serial data to a remote Arduino. The hack uses a FET, a capacitor, and a few resistors. They didn’t quite build a real modem with the audio.

A MAX7219 drives the display, and the brains are an ATmega8. It’s straightforward to send new values: a start byte, a CRC, the data to display, and an end byte.

The CleO Comes complete with 20 tutorials and 20 projects allowing you to learn more about the Arduino platform and using the TFT display to show your data and results as well as any navigation ...