I have setup a hackduino following this instructables http://m.instructables.com/id/Perfboard-Hackduino-Arduino-compatible-circuit/step6

This connects AREF to 5V directly. My understanding now is that this is wrong.

Is this a problem at all if I do not plan on reading or writing to analog pins of my Arduino?

Do I understand it correctly that the default is to connect the AREF via a 100nF capacitor to GND?

I have seen several questions regarding AREF that seem to indicate that, however most of them use analog read or write.


The AREF pin has no required connection.

If an external reference is needed, it can be connected to the AREF pin, but then care has to be taken to not connect AREF to an internal voltage source.

If an internal reference is used, the "best practice" is to externally decouple the reference by connecting a small capacitor between AREF and ground, but this is not an absolute requirement and you will usually "get away" with not connecting it.

If the ADC (analog pins) is not used, you can safely leave this pin unconnected.

  • 1
    \$\begingroup\$ A small follow-up: I have ordered some PCBs where AREF is falsely connected to 5V. Will I get away with this for my prototype as long as I never use analog read or write? \$\endgroup\$ – Felix Lamouroux Oct 14 '15 at 10:45
  • \$\begingroup\$ As long as you don't set up the ADC to use an internal reference voltage, everything will be fine. you can even read analog voltages. \$\endgroup\$ – Brog Oct 15 '15 at 7:54
  • \$\begingroup\$ Another thing: Analog write is as far as i remember handled by pulse width modulation and is as such independent from the analog reference. \$\endgroup\$ – Brog Oct 15 '15 at 7:57

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