Many designs use a 100nF capacitor

Many designs use a 100nF capacitor at the AREF pin, like thedesign of Markus F. too. As long as the reference voltage of the ADC is never changed, this is agood solution. The software of the TransistorTester for the ATmega168/328 uses a automaticselection of the internal 1.1V reference voltage of the ADC, if the input voltage is below 1V .With this solution a better resolution of the ADC can be reached for little input voltages.Unfortunately the switching from 5V to 1.1V reference is very slowly. A additional wait timeof 10ms must be respected for this reason. With changing the capacity value to 1nF this waittime can be reduced significant. I have not noticed any degration of measurement quality withthis change. Even a removing of the capacitor has no significant change of measurement results.If you prefer to leve the capacitor unchanged, you can remove the option NO AREF CAP inthe Makefile to activate longer wait times in the program.