AREF pin connected to +5V on Olimexino-328

Started by mcmusic, June 09, 2013, 05:05:35 PM

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Hi there,
I own an  Olimexino-328 board since a while and was quite happy with it.

However, today I tried to use the command analogReference(INTERNAL) for reading in low voltages with good resolution - see .

It does not seem to work - analogReads should be made to the 1.1 Volt internal reference after that. But it reads with 5.0 Volt reference as with analogReference(DEFAULT);

I have spotted int the Olimexino schematic R6 (NA) with zero Ohms, connecting AVCC and AREF.

Why on earth is that?????  Is this one of the claimed features "We made our design noise immune"?

According to the schematic, as R9 R10 R11 R14 and SR1 (provisions for precise Aref source, which is a good idea) are not on the board, I thought NA means "not added" or "not assembled on the board". However R6 seems to be not a part but a copper connection on the printed board. If this is true, the Olimex-328 is NOT COMPATIBLE with a standard Arduino board, because all analogReference commands can not work, which should not be.

Questions to whoever can answer them:

1) Is R6 implemented with zero Ohms in the actual board? According to my measurements this is so.
2) Did I ruin the internal 1.1 Volt reference with programming analogReference(INTERNAL)? This sort of shortens the 1.1V source to +5V AVCC via the R6, which should not be there.
3) If I want to use the ARef pin for better resolution, can I cut the R6 copper trace on the board? Anything else what I should / could do?
4) Which disadvantages will I have after doing step 3) ?
5) If there are no disadvantages, why did Olimex implement R6 at all, denying the use of the standard Aref pin altogether?

Thanks for your answers,


Hey mcmusic,

Please cut the wire between the pads of R6. Instead of connected the pads of R6 should be disconnected by default. This will be fixed in the next revision of OLIMEXINO-328.

Best regards,
Technical support and documentation manager at Olimex



can someone guide me to R6 position? I have a Rev.C board and would like to apply the fix.

Olimexino328 section is totally empty on the Wiki, so I don't know where to find the schematics and I can't spot R6 on the board.




Nevermind, found it myself (it is more or less at the center of the board, near the text "FTDI BASIC").