Damian needed to get telemetry from his off-grid solar system 150 feet away, but didn't want to spin up another unreliable WiFi device. Instead he came up with a clever solution that involves using ultrasonic transducers as the physical layer of a software defined communications system instead of RF transmitters and receivers.

Having worked on RF communications systems before, Damian knew that the same  concepts apply no matter what the physical layer of communication is. His system called SDU-X uses two ultrasonic transducers mounted on 3D printed parabolic dish's to increase the directional gain, and an Arduino Nano with amplifiers and a Digital to Analog (DAC) converter for the ultrasonic transmission.

His post explains the hardware and protocol implementation, as well as explaining the Arduino code that he's released for free. The code and 3D printer models can be found on Thingiverse.