AVR-Chat

Also, be sure to keep your I2C pullup resistors (Rp) as low as possible,
down as far as 1K is allowed by the spec.  This will help help your
rise-time and speed with that long shield capacitance. Also it may
help your noise immunity in that boat-electrical environment.

Steve Hodge wrote:
>
> Thanks. I'm aware of ground loop issues. My boards always have jumpers to
> allow disconnecting ground lines when otherwise there would be multiple
> ground connections. Similarly for the shield, so that it can be 
> grounded at
> only one end. The application is for a boat, which at times has strong
> radio transmissions all through it. My approach is that shielding cannot
> hurt (properly implemented).
>
> Steve
>
> From: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> 
> [mailto:AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com>] 
> On Behalf
> Of David VanHorn
> Sent: Tuesday, March 31, 2009 9:46 AM
> To: AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com>
> Subject: Re: [AVR-Chat] i2c and twisted pair
>
> > I have other reasons for wanting to use Cat5: shielding, quick & easy
> > connect/disconnect, relatively cheap and easy to make up cables, and for
> my
> > situation cables that are flexible and easy to run convoluted paths is
> very
> > important. I also have other uses for the remaining conductors in "RJ45"
> > cable, so that, plus shielding, is the reason I'm not just using 
> "RJ11" or
> > "RJ12" modular cable (I've never been able to find such cable that is
> > shielded).
>
> Shielding is tricky, and may not buy you much.
> If you have more than one ground connection between the systems, then
> you risk "ground loop" noise.
> Basically, any current flowing in the grounds gets expressed as a
> voltage, which hoses up the logic thresholds.
>
> Belden has all sorts of shielded cables, solid, stranded, 2 pair, no
> problem.
>
> [Non-text portions of this message have been removed]
>
>