I've made a capacitance meter based on this tutorial , but with a few modifications, and i'm getting some errors. I've tested both on a protoboard and on simulators, and both worked perfectly, but when i moved to an universal board where i soldered everything the values read were all wrong.
With anything up to 500nF it is showing less than 3nF, and with a 10uF cap i'm getting 16nF. I think that maybe there is a problem on the soldering which is causing that, since on the simulation i'm getting the right value, and i don't think that the variance on resistors and whatnot would made such a big difference on the readings.
Link with the code (Some comments are written in portuguese)
The schematic is the same as the one on the tutorial, i just used the Atmega328 standalone and used a LCD screen.
Here are some pictures of the circuit: LINK
Maybe the problem is on the Aref pin, here it says to put the the pin to 5V, which was what i did, but i've also read that i need to use a 100nF capacitor there for decoupling, do you think that it could be it?
I just tested again on the protoboard using the arduino board (i don't have another crystal to test the atmega standalone), and it is working normally.