ADC analogRead change when supplied from 2xAA

Hello all, I'm noticing a very strange behaviour of analogRead. Scenario: - Pro Mini 8MHz 3.3v - LM35 attached to analog pin 2

If supplied at 3.3v I read an analogRead of 180 -- LM35=0,189v measured with tester If supplied at 2.9 (from 2xAA 1.5v) it reads 150 -- LM35=0,189v measured with tester

I use analogReference(INTERNAL) therefore it should (?) be not dependant from external supply.

Anyone experienced something similar ? Many thanks in advance Ciao Pietro

Some new test.... I experienced that supplying the board from VCC of JP1 (the 6 pin used to program) everything works. If I use the VCC of pin 4 of the JP2 then I have different reads (wrong). I also noticed that between the 2 VCC there is a resistance of 8 Ohm. Will investigate the PCB.

Any ideas ?

Thanks Ciao Pietro

The LM35 needs 4V ?
So everthing below that is invalid ?
Please check the datasheet. I think I remember trying to use the LM35 for a battery operated device, but I had to buy another sensor.

Hello Caltoa, I went through this limitation but I found that if operated to a normal ambient temperature this is not an issue. On my board it perfectly works at 2.8v supply voltage. The problem is in the board itself where there's a different behaviur depending on the VCC pin I use to supply voltage.

Ciao Pietro