On Wed, Oct 23, 2013 at 10:42:05AM +0800, Andrew Elwell wrote:
> Leaping in on this for ideas:
> 
> > That said, the voltage drop should be *unevenly* distributed between Vcc
> > and GND, so don't have 2 Vcc wires + 2 GND wires but rather 1 Vcc wire +
> > 3 GND wires. Voltage drop on the Vcc line isn't "seen" by the bus
> > protocol, on the GND wires it's causing problems.
> 
> In my setup I'm planning on driving 20-30 DS18B20s along a piece of
> ~20m cat5 (or higher) cable -- should I therefore use a couple of
> spare paies as extra ground connections (such as the brown / w/brown
> ones that would otherwise be unconnected?)

I would move the power to the other end of the cable if possible (you
could use a 5V wallwart at the computer end and run it through a
separate pair, with just a cap on the remote end).  Better if you can
put the wallwart at the remote end too (minimise crosstalk).

njh

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