A few folks had chorders that worked fine with the atmega8 but would not work with the atmega168. At Mikkel’s suggestion we tried changing the diodes.
We found that while the atmega8 will work with diodes rated at 1 watt, atmega168 will not work properly in those same circuits. Using diodes rated at 500 mW works for both the atmega8 and the atmega168.
The digikey part number on the component page is for 500mW diodes.
— Greg Priest-Dorman 2010/03/21 17:18