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i2c over cat5 sender/receiver/hub

Posted: Mon Jan 13, 2014 8:39 pm
by back_ache
I am about to start on my own (basic) home automation, in my case by having two runs of cat6 to each room.

One thing I thought about is putting a temperature sensor in each room running back to a central board (an electricimp in my case) I thought of doing it by simply crimping a cat5 connector to a temperature sensor, whilst I should be able to "get away" with running its i2c protocol over the cat5, its a bit of a bodge.

What would be ideal would be to have simple cheap boards that "drive" i2c across structured cabling, you could even have a "hub" at the centre so as not to have a have an i2c universe per sensor.

I thought this idea could be used to enable a number of cheap remote i/o options for those wanting centralised brains (for whatever reason)

Re: i2c over cat5 sender/receiver/hub

Posted: Mon Jan 13, 2014 11:24 pm
by angusgr
Hi back_ache,

Thanks for the suggestion! There are certainly some chips out there designed to drive i2c over longer cable runs, so we could look into incorporating some into interface boards.

For what it's worth I had a quick look to see how necessary this is. i2c is officially limited to 400pF total bus capacitance, and CAT5 is something like 50pF/meter, so it's unlikely very long cable runs will work without something in between (although they might depending on the specific driver/device combinations you choose, the data rate, and the size of pullup resistor.)