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Author Topic: I2C Wire Length  (Read 2930 times)
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Edmonton, Canada
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Hello,

I'm looking at using Arduino's to control a home-made garden watering system. Right now I'm thinking of having one main chip that takes input, handles scheduling tasks, and controls several slave units. The slave units would be spread around the yard and their sole task would be to turn water on or off at their station depending on what the master wants them to do. Each slave would be optocoupled to a powered valve and would include safety stop measures in case anything breaks down.

Anyways, my big question is how to connect the Arduino network together? Obviously, an I2C bus comes straight to mind and would be perfect, except I'm worried about the lengths of wire that would be needed. Reading the ATMega specs, I can see that there is a maximum line capacitance of 400 pF, but I have no clue what the line capacitance of copper wire is, and Google failed me completely there.

I don't care about speed.. I'm happy to go as low as possible (about 500 Hz) to make it work, as I've read that slower speeds can handle longer lines. Unfortunately I don't know much about this stuff.

Can anyone here shed some light on the subject for me please? Where I should be looking, or if anyone has done something similar, what have they done?

Thanks so much!
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Have a look at Two wire serial bus for range 20-30m?

One recommendation is to use I2C buffers

HTH
GB
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Edmonton, Canada
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Thanks! Apparently I just suck at searching.
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