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AREF again!

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#1 Philip



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Posted 25 January 2013 - 04:59 PM

Hi All,


I have looked but been unable to clarify the situation regarding AREF on the new Netduino 2.  Can someone help?


For the original Netduino we had REVA without AREF connected and REVB with it connected (I think).


I have just bought some Netduino 2s, and the board (REV.A) labels the 'digital pin 15' (after 12, 13 and then GND) with a blank.  The web page labels the GND + blank as POWER.  The new Netduino 2 schematic diagram at:

labels it as AREF, but then shows that it is unconnected (so it isn't AREF).




Further to this, if AREF is connected to an internal reference, then presumably we must not connect it to anywhere else (like a 1V reference) for obvious reasons.  If the AREF pin is connected to the ARM (VDDA ?), then without a connection there is no reference for the AD converter (and therefore we must always provide one).


Now, I also notice an IOREF pin has sprung up beside /RESET. What is the purpose of this (and might I need to connect it to AREF)? 


Thanks all - still a great product!



#2 Mario Vernari

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Posted 25 January 2013 - 05:07 PM

Phil, looks like the "old" ARef is now unconnected: simply the ADC rely its reference on the +3.3V rail.

Also, the IOREF is something unknown to me too, as usefulness.


Biggest fault of Netduino? It runs by electricity.

#3 Chris Walker

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Posted 25 January 2013 - 05:17 PM

Hi Phil, With Netduino 2 and Netduino Plus 2, AREF is now always 3.3V. If you pull your analog sensor's power from the 3V3 header, you should be good to go. There are quite a few reasons why we eliminated the external AREF from the gen2 boards. There is a large variation in allowed voltages on Arduino-style boards, and we found almost all users exclusive used the internal AREF on the gen1 boards. So to simplify things a bit we moved AREF to always-internal and traded the cost of the seldom-used external AREF circuitry for more horsepower and other extra features instead. The IOREF pin is simply wired to the 3V3 header. This lets shields know what voltage digital signals use, and enables compatibility with all the new Arduino "R3" shields. Chris P.S. For any users who really need an external AREF, Netduino 1 and Netduino Plus 1 boards are still available at a discounted price. Lots of commercial customers use Netduino Plus 1 in their projects, so we're continuing to manufacture those on an ongoing basis.

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