Arduino Uno AREF pin normally high 5v. Normal?

Development Boards Arduino
1

Hi friends.

I power up the UNO, and check AREF for voltage and find 5V. Is that normal, I need to input a reference voltage less than 5V and wonder why this is happening? Is there a jumper I need to set up or is this normal?

Thanks again.

2

Normal, but not good. From the datasheet: “The internal voltage reference options may not be used if an external reference voltage is being applied to the AREF pin.” IIRC, setting up the A-D to use Vcc as a reference actually causes the Aref pin to be connected to the Vcc.

I’m not sure what that means in the case of Arduino, where the core will turn on the A-D with Vref=Vcc. I suppose that if you change it back “real soon” in setup(), and your reference is current-limited and prepared to handle a bit of a glitch, things should be OK; you’d only be talking about a couple of microseconds worth of glitch…

3

You need to change the Aref from default to external.

http://arduino.cc/en/Reference/AnalogRe … rence.AREF