Goldilocks with the Adafruit PN532 NFC Shield

An advanced Arduino-compatible board with ATmega1284P and ATmega32u2 MCUs for experienced users. More RAM than a Mega, but in a convenient Uno-style form factor. [Product page]
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Joined:Thu Sep 19, 2013 9:09 am
Goldilocks with the Adafruit PN532 NFC Shield

Post by spidie » Thu Sep 19, 2013 9:15 am

Finally getting around to using my Goldilocks for something. Looks good.

One problem I am having is using it with my Adafruit PN532 NFC Shield

Just doesn't seem to want to detect the PN532. I've put it back on one of the Elevens and it's fine, so I'm assuming it's something different about Goldilocks that's causing it. All the LEDS are on correctly so power doesn't seem to be a problem - is something perhaps interfering with the I2C. The shield has I2C on analogue pins 4 & 5 with interupt on Digital 2.

Any ideas?


Joined:Fri Jul 19, 2013 6:17 am

Re: Goldilocks with the Adafruit PN532 NFC Shield

Post by feilipu » Thu Sep 19, 2013 1:54 pm


yes. Can take a wild guess.

The Goldilocks is wired out of the box for Arduino R3 compatibility. This means that the I2C bus is NOT present on the Analogue 4 and 5 pins. They are up near the AREF pin.

However, we know this is an "inconsistency", and many older (or even new) shields don't implement this layout.

To work around this please join the two solder bridges on the rear of the Goldilocks. This will bring the I2C pins back onto A4 and A5.

See also here I2C Headers

Make sure you're not using A4 and A5 at all though, or you will disturb the I2C bus. Also, if you're worried about power consumption, you can optionally turn off the analogue circuitry associated with A4 and A5.

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