dhenry:
Thus, the lsb approach. It actually doesn't rely on the randomness of a signal on the adc pin, but the randomness of the last digit returned by the adc process. You can tie the pin to a known voltage (Vcc or ground), yet the adc's lsb is unstable.
Nope. The technique failed again. Analog input 1 ... failed. Analog input 2 ... failed. Speed up the ADC clock ... failed. Speed it up even more ... failed. Set it to the value used in the core ... failed.
It actually doesn't rely on the randomness of a signal on the adc pin...
It may not but it most certainly does not work the way you described.