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Author Topic: I2C questions (which pins?)  (Read 759 times)
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Hello,

I'm trying to connect a MAX1236 via I2C to my Arduino Pro board with ATMEGA328.

What is very unclear to me is which pins are used on the Arduino board for SDA/SCL

I've tried pins 20/21 (red this somewhere) also 27/28 (which doesn't work either), connecting a scope to these lines did not show any activity.

Also, how can I override the default settings (I would like to use 27/28 as they are default for ATMEGA328)

Any help greatly appreciated !
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The correct pins are 27 / 28, these are physical pin numbers on the chip used as A4 & A5
Be sure to add 4K7 pull up resistors to each pin.

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Also, how can I override the default settings
You can't it is built into the hardware.
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Are the internal pull up resistors not being used ?
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Yes but they are too big to do the job correctly.
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Great, I'll try this tonight!
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This explains what the signals look like without the pull up resistors:-
http://www.dsscircuits.com/articles/effects-of-varying-i2c-pull-up-resistors.html

If you are having difficulty connecting to things run an I2C bus scanner, this is just one of them:-
http://omarfrancisco.com/i2c-bus-scanner/
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It works now, thanks !
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