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Aref on Arduino Uno

LarryH

New Member
Hi, am trying to get an Aref input on a Uno. Wanted to get a lower voltage than the 1.1 internal so tried a 0.6V Precision shunt regulator, a Zetex ZXRE060.

Built a little shunt regulator circuit and the Vout is .6V but when I connect to the Aref, the voltage drops to 0. Here is the link - am using the circuit ifn figure 3 -http://www.diodes.com/datasheets/ZXRE060.pdf

There is something on the data sheet that says there is a precision internal reference that can turn off the Vout which I do not understand.

I am inputting 3.3V from the Uno. (device will accept 2-18V input)

Would changing the value of the resistor or capacitors allow the Vout to connect to the Aref without dropping to 0?

Perhaps I chose the wrong device to act as a voltage regulator?

Thoughts or suggestions?

Thanks
 
Last edited:

Mike odom

Active Member
This looks like an ok part for an ADC reference pin... will sink up to 15mA, and using a 1K source resistor yields only 2.7mA.

Are you sure it's connected correctly? Did you set the AREF pin for external? Is the FB tied directly to Vout? Is there a 1K resistor between the Vin and Vout/FB pins?

The only thing I see about it turning the output off is if the FB is lower than .6V, which it would turn the output off so that it can come up.

The way this part works is to sink current through the source resistor (fig 3, 1K tied between Vin and Vout) to drop voltage across it until the FB is at .6V. If you want a .6V regulator, you connect the Vout to the FB pin directly. If the FB voltage goes below .6V, the Vout turns off and quits sinking current so that the voltage dropped across the source resistor is less and the voltage at Vout (and FB) goes up. In the configuration of figure 3, when the Vout sinks 2.7mA, the 1k resistor will be dropping 2.7mA x 1K = 2.7V, so 3.3V - 2.7V = 0.6V.
 

ChrisP58

Well-Known Member
Make sure you have the uController configured to use the AREF pin as an analog input. Sounds like it might be configured as a digital pin outputting a zero.
 

Mike odom

Active Member
Make sure you have the uController configured to use the AREF pin as an analog input. Sounds like it might be configured as a digital pin outputting a zero.
unlike the PICs, the ATmel processors can only program the AREF as external input, AVCC, or internal reference.
The Aref pin cannot be used as a digital I/O.

AVR_AREF.JPG
 

ChrisP58

Well-Known Member
unlike the PICs, the ATmel processors can only program the AREF as external input, AVCC, or internal reference.
The Aref pin cannot be used as a digital I/O.

View attachment 69431
Sorry, I didn't know that. From my experience with PICs, that seemed to be the most likely reason why an analog voltage connected to a pin would be zero.
 

LarryH

New Member
Thanks for the responses. Mike, your description of the process put me on the right track and all is working fine. Appears the Vout was being turned off internally in the IC - put a different resistor in the circuit and voila.
It is really nice as a noob to post a question and get quick and accurate answers on this forum;)
 

Mike odom

Active Member
a tutorial on what? the AREF pin, or the whole Arduino? Best place to start is to read the data sheet/manual.
 

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