What are these pads on Arduino Duemilanove for?

Here is a photo of my Aruino Duemilanove clone, what are these pads (they exist on original board too):

Thanks in advance!

Did you try checking for connections between them and other pads on the board with a multimeter? I've thought about doing that, but never got around to it.

Haven't checked yet, but I checked Eagle board file -- it seems they are not connected anywhere.

They might be fiducial marks used to help the pick & place machine find it's way around.

Normally there would be three of them though I think.


That's because board is double sided?

I can't find the third (can't look into Eagle board layout right now):

They are indeed fiducials:

You only need 2 of them. Only 1 provides a known reference point (an “origin” so to speak). Two of them provides both reference points and information on whether the board has any rotation.

Sometimes more are used when there are super-fine-pitch parts that need extra care in placement, and then a “local fiducial” will be placed close to the part(s) so that there is even more accuracy in setting the reference point when placing that part.

The Aussie Shield: breakout all 28 pins to quick-connect terminals

Thanks for the detailed response!

I read about these a while back, very neat!

There's a third partially hidden by the DC input.