There is a software-only USB stack for AVR microcontrollers, and it has a example section with LED and Display projects: http://www.obdev.at/products/vusb/prjd

There is a software-only USB stack for AVR microcontrollers, and it has a example section with LED and Display projects: http://www.obdev.at/products/vusb/prjdisplay.html http://www.obdev.at/products/vusb/prjdisplay.html Especially this project is almost identical, but has a different form-factor: http://www.vandenbrande.com/wp/converting-a-led-cube-into-an-extreme-feedback-device/ http://www.vandenbrande.com/wp/converting-a-led-cube-into-an... (look at the schematics, and keep in mind that the ULN2003 is not needed for driving lower-power LEDs, and there are microcontrollers running the VUSB stack that can use their tunable internal RC oscillator, so the XTAL can go away, too...) For the cost, it's difficult to say what's a reasonable amount: I like the idea to retrofit a general purpose notification LEDs to computers, but have no immediate personal use. For one-off projects every "maker"/hacker/tinkerer/electronics-enthusiast I know has maybe 10 unused boards of various kinds laying around where one could retrofit such an indicator (in a ugly way, I admit) in 10 minutes. The only way this could be made accessible to the normal non-savy home-user would be to have an assortment of ready-made plugins for all major email-clients, instant-messaging, twitter, skype or long-running PC tasks (has this upload already finished?)... Maybe Outlook notifications? And creating all those will be a pain in the...