Water Optic Communication

After watching an episode of the show Modern Marvels on the subject of glass, including a bit of time spent on fiber optics, Mike Kohn decided to make his own light-based data transmission device. Instead of glass, however, he used water as the transmission medium, filling a length of curved tubing, and capping it off with an LED.

He cleverly used tubing with a roughly 5mm inner diameter, along with a 5MM LED as the transmitter and a 5mm photodiode, creating an easy way to seal water inside. A UART cable sends data from a terminal program running on a nearby computer to an ATtiny85-based LED driver circuit, which pumps signals in the form of light to the receiver. On the receiver, a second ATtiny85 receives this signal using analog-to-digital conversion, and passes it to a second UART cable.

This info can then be read on a second terminal “at the speed of light,” or at least at 9600 baud over UART. The video below shows the process in action, and features an experiment without water, in case you’re wondering if the tubing itself is doing the transmission work. The circuit implemented here also has everything needed for two-way communication, though Kohn chose not to pursue that functionality.