If you’ve ever spent time working with AVR microcontrollers you’ve probably set the fuse bits incorrectly at least once. The ATmega fusebit doctor will automatically repair the fuse bits and get you back in business until your next mishap. The ATmega8 that powers the device has the chip signatures for the ATmega family stored inside so it will automatically detect which chip you’re trying to ‘unbrick’. From there it looks up the correct fuse bits and resurrects the sick microcontroller. This is useful in recovering a chip that has serial programming disabled, used the reset pin as I/O, or just enabled an external clock without the necessary hardware to deliver on that feature.
This magic is taken care of by using High Voltage Parallel Programming. We’ve seen HVPP used in the Arduino rescue shield and it is a valuable feature of the AVR Dragon, our favorite AVR programmer, as well as others. Still, you can hardly beat the ease of plugging a dead chip into this board and pressing one button. Oh, did you brick a member of the ATtiny family? There’s a rescue board for those too.