Here’s an external display meant to help you keep track of your computer’s status. It connects via USB and is driven by a PIC microcontroller. It listens for a small set of commands, using those to implement a simple control protocol to drive the screen.
[Andrew Gehringer] designed the device around a PIC 18F2550, which offers native USB control. He’s using Microchip’s USB stack to enumerate the module as an HID device. It listens for commands 0×10 through 0×23. These clear the display, write strings to each of the four lines of the display, and switch the LCD backlight. Of course the project includes a program [Andrew] wrote to feed the display. It has a GUI which let’s him decide what information is displayed and how it is formatted. This helper app hangs out in the system tray for easy access.