We’ve seen some pretty cool projects that use blinking lights on a PC monitor to transfer data to a microcontroller. We did a little research, and here are some example projects we’ve found.
This project uses two photo transistors to read a bar code from the monitor. One handles the clock, while the other has the data. The data is read as the clock changes from black to white.
Here is the same project with a different variation of the transmission system. Instead of bar codes, two small rectangles flash to give the data and clock signals.
Cheap light-based PC to microcontroller communication - [Link]