Re: I2C off board distances

From: Hans-Bernhard Broeker (broeker_at_physik.rwth-aachen.de)
Date: 09/17/04 

Date: 17 Sep 2004 13:19:15 GMT

Colin MacDougall <colin@blueyonder.co.uk> wrote:
> Has anyone any experience of running an I2C bus from
> a PCB to a remote I2C device?

No experience, but a caveat: that's not at all the kind of operation
I2C is designed for. It may work, sure, but you should be aware
you're stretching a design quite a bit beyond its intentions.
Problems are almost guaranteed.

> I am thinking of connecting a remote Dallas Semiconductor I2C
> temperature sensor IC to a micro over a length of 4 or 5 metres of
> wire.

Their "1-wire" technology might be preferrable for that usage.

> Could I run this at the typical 400 KHz clock speed with
> a decent bit of screened cable ?

Even if you could, why would you want to? I would think ambient
temperatures in a room change at speeds on the order of at most 1
degree/minute, so anything faster than one reading per second per
sensor would be complete overkill, and one reading every minute might
still be perfectly enough. You don't need anything as fast as 400 kHz
for that. 

-- 
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

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