Hi, I’m using your USB k8055 kit for my project
I test analogical ports 1 and 2 from 0 to 5 volt ; I measured Vin with a bench precison tester (+/- 0,05 mV)
I checked a big difference from Vin and k8055 meauseres!
for example:
from 0,1 to 0,5 Volts the biggest difference…30% to 5%
from 0,6 Volts to 2 Volts 5% to -1%
from 2 to 5 Volts -1%…0%( for 3 Volts) …+1%
The K8055 has 8-bit analog-to-digital converter (ADC) with an accuracy range of +/- 0.39% (1/256) of full scale. With a 0-5V input this is an accuracy of +/- 0.0195V – at ALL input values.
So, with a 0.1V input the very best accuracy would be +/- 19.5% (0.0195/0.1), however there is also the accuracy of the input conditioning circuits as well, making 30% error likely;
With a 0.5V input the ADC accuracy is reduced to +/- 3.9% (0.0195/0.5), making your observed 5% likely;
Similarly:
0.6V is 0.0195/0.6 = 3.25% possible error;
2.0V is 0.0195/2.0 = +/- 0.98% accuracy;
5.0V is 0.0195/5.0 = +/- 0.39% accuracy;