If you have an old Sinclair ZX81 that can't be brought back to life (as using it for any other reason would be sacrilege if it worked), you can keep it alive in spirit by converting it into a USB keyboard. As you know an Arduino board can emulate USB devices very easily using the USB library, so with a little hardware the Sinclair can interface with the Arduino, and your'e set. For example:
For more information, the schematic and Arduino details visit the Tynemounth Software blog. And we're on twitter and Google+, so follow us for news and product updates as well.
If you're looking to embed an Arduino-compatible board in your own USB-related projects, consider our Freetronics LeoStick. Apart from being one of the smallest Arduino-compatibles on the market with USB, it also has an onboard RGB LED and piezo for sound and knock detection. Furthermore as it has the latest Leonardo firmware, the LeoStick can easily emulate a USB keyboard, joystick or mouse:
