Am Sonntag, 4. März 2007 00:53 schrieb Wizard:
> >
> > If you power a lot of onewire chips (and peripheals) over a thin, long
> > cable, the GND niveau at the end of the cable may reach 0.7V due to the
> > current through it. This disturbs the onewire function for chips at the
> > end of the cable a lot.
> >
> > Kind regards
> >
> > Jan
>
> Hey i have my DS18s20's all over the house my line length is about 300
> feet in total it was difficult but i have 32 ds18s20 and 4 DS2408 all
> on the same network
> just add one step at a time.
>
The problems start whith currents >100mA and cables as thin as flat telephone
cable. And with lots of intermedient connectors. A DS2408 driving 8 20mA LEDs
is limiting cable length to ~20m when using 0.07mm² wire gauge phone cable.
This problem is arising any time you are using the GND line as power return.
If you plan to power devices over such a cable, it is wise not only to provide
a separate power wire and *one* additional GND wire, but as much GND wires as
possible.
5V or 12V over a thin cable will be subject to voltage drop, too, but there it
is not crucial, as you can apply a slighty higher voltage at the start of the
cable. That trick is not possible with elevated GND potentials.
Kind regards
Jan
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