Max 3,3V analog input

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi!

Im using a accelerometer that runs at 3,3V.
My arduino mega whants 5V to get all the benefit of 10bit analog input.

Now I get a max analog read value of 680 and I need it to be 1023.

Thanks!
/Anders

2

You can use an external reference voltage of 3.3V. This will give you the full 10 bit resolution of the ADC at 3.3V

Search the forum for analog + vref to find info on how to do it.

3

Can't you just power the accelerometer from the 3V pin on the Arduino instead of the 5V one, and use 5V elsewhere in the circuit?

4

No that wont help. If you use the built in 5V ref. voltage and apply a max of 3.3V to an analog pin you wont get the full 10 resolution frm the ADC

5

Thanks!
I connect the 3,3V power supply to the AREF pin.

And use this in my code:
analogReference(EXTERNAL);

It works like a charm!

/Anders