I2C R3 shield headers

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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stryker
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Joined: Sat Jan 14, 2012 2:44 pm

I2C R3 shield headers

Post by stryker » Sat Sep 07, 2013 8:44 am

Hi

Just wanted to clarify - is this like an R3 Uno where A4/5 are electrically the same as the additional I2C headers, or are A4/5 independent of I2C on a Goldilocks and can be used concurrently with I2C for other sensors ?

Thanks
Geoff

feilipu
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Joined: Fri Jul 19, 2013 6:17 am

Re: I2C R3 shield headers

Post by feilipu » Sat Sep 07, 2013 10:04 am

Geoff,

A4 and A5 are electrically different to SDA and SCL (I2C). They are on different I/O pins. This is similar to the Arduino Leonardo, although the actual pins and ports are different.

Unlike in Arduino Leonardo, there is the option to reversibly join a solder bridge on the rear side to link the SDA and SCL pins to A4 and A5 to support older (Pre-R3) shields that expect SDA and SCL at the "normal" Pre-R3 location.

If you do this (bridging) you'll want to make sure you keep the A4 and A5 pins as inputs too, though this is the default on RESET. Also (optionally) turn off the ADC for A4 and A5 too, if you're concerned by power consumption. Having these pins swinging along with the I2C signals may cause the internal ADC sampling capacitors to charge and discharge too.

Regards, Phillip

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stryker
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Re: I2C R3 shield headers

Post by stryker » Sat Sep 07, 2013 10:25 am

Thanks Phillip. That's exactly what I needed to know.

Cheers ! Geoff

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