Extremely unstable analogReads

[JohnRob]

@ma_wu

was there this morning when the system was still inacurate and measured Vcc, it was 5,08V at that time. Some hours later it dropped to 5.02V. So it makes sense that the AnalogRead differs.
That's why i wanted to use the LM4040, but unfortunately i purchased the 5V-Version.
Because there is hardly an overhead driving a 5V-reference from Vcc, the voltage dropped as mentioned before to 4,84.
When Vcc went up above 5V to 5,08V, i think the LM4040's reference voltage has also risen, since it is supposed to provide 5V.

You can:

1. Try to power the Arduino with 5.5V and use your current reference.
2. Use the current reference and divided it down to 4.1 volts or so. Add a 0.1 µF cap on the external input pin.
3. Use the 1.1V internal reference and divide down the inputs to be below 1.1V.