You tried to read from 2.33V to 3.73V, you can not use analogref(2v56) , you should use analogReference(EXTERNAL) and setup EXTERNAL voltage as 3.80V. Wire up 3.80V voltage regulator and feed it output with resistor into AREF pin.
You tried to read from 2.33V to 3.73V, you can not use analogref(2v56) , you should use analogReference(EXTERNAL) and setup EXTERNAL voltage as 3.80V. Wire up 3.80V voltage regulator and feed it output with resistor into AREF pin.