Use Arduino 3V3 for external AREF

Forum 2005-2010 (read only) Hardware Interfacing
1

I have yet another AREF question:

I'm interfacing an MMA7260Q accelerometer which uses 3.3V power and has an analog interface. I'm powering it straight from the Duemilanove's 3V3 supply. Is there any reason I can't also connect the Arduino 3V3 line to AREF, so I can get the full 10bit resolution of the ADC?

Also, after reading the discussion on http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1236499795 I take it that I shouldn't put a resistor between them, and that all I need to do is call analogReference(EXTERNAL) before I call analogRead(). Right?

2

You can use the 3V3 supply for the accelerometer (assuming it doesn't need more power than the FTDI chip [which supplies the 3V3] can put out), but I'd suggest an inductor (or ferrite bead) between the supply and the Aref pin, as well as a filter cap on the Aref side of the inductor. That's to keep as much noise out of the Aref pin as you can.

Using the values for the inductor and cap on the Arduino schematic would be fine for your inductor and cap.