Re: Re: 1-Wire Headache

[Jon Payne <jgpayne@xxxxxxxxxxxxxx>]

I think that's unlikely, the fact that you can read the sensor means
things are generally ok, it's just that you cannot initiate a temperature
conversion - which does generally mean it's not getting enough power: DQ
not held high long enough, or droopy.

Having said that I know nothing about the temp08, you could try adding a
stronger pullup resistor to DQ as suggest in the 1-wire trouble shooting
docs.

Cheers,
Jon

----- Original Message ----
From: Marc Fuller <groups@xxxxxxx>
To: ukha_d@xxxxxxx
Sent: Wednesday, 18 July, 2007 1:28:09 PM
Subject: Re: [ukha_d] Re: 1-Wire Headache


Hi Stuart,

The com port is not providing the power. The temp08 has a power supply
that provides the power to the bus.

I am beginning to think there may be a problem within the cable. I think
I'll replace it and see what happens.

Cheers

Marc

Stuart Poulton wrote:
>
> Hi Marc,
>
> I suspect that the problem is that the comm port can't provide the
> required current.
>
> I see that it's possible to provide the temp08 with a 12V supply via
the
> screw terminals, I'd recommend doing this. I've stayed away from
> parasitic power where ever possible with 1-wire and have found the
> results to be very promising.
>
> Cheers
>
> Stuart
>
> On Wed, 2007-07-18 at 11:27 +0000, marcrfuller wrote:
> > Hi Quinten,
> >
> > The sensors are DS18B20's
> >
> > If I understand the term parasitic power correctly then yes they
are
> > using parasitic power - e.g the power is taken from the TEMP08
via the
> > comms line.
> >
> > Cheers,
> >
> > Marc
> >
> > --- In ukha_d@xxxxxxx <mailto:ukha_d%40yahoogroups.com>,
> Quinten Uijldert <yahoogroups2@...> wrote:
> > >
> > > And another question is if you are using parasite power or
not? And
> > > what Dallas sensors they are? DS1820 or DS18S20?
> > >
> > > On 17 Jul 2007, at 19:42, Stuart Poulton wrote:
> > >
> > > > Marc,
> > > >
> > > > 85c is the reading that is returned as an error,
normally that a
> > > > conversion wasn't able to be made.
> > > >
> > > > 2 questions
> > > >
> > > > 1 - Are you making connections to all 3 legs of the
sensors ?
> > > > 2 - What sort of cabling are you using.
> > > >
> > > > I've successfully run 1-wire over 100m of cat5, using
modules that
> > > > daisy chained (modules of my own design)
> > > >
> > > > Cheers
> > > >
> > > > Stuart
> > > >
> > > > On 17 Jul 2007, at 17:49, Marc Fuller wrote:
> > > >
> > > >> Hey Guys,
> > > >>
> > > >> Just bought myself a TEMP08 to replace my Quasar
logger. It's all
> > > >> up and
> > > >> running and 3 of the sensors are working perfectly.
My problem is
> > > >> with
> > > >> the fourth.
> > > >>
> > > >> For some reason the fourth sensor that is at the
end of the bus,
> > > >> keeps
> > > >> showing a temperature of 85c, which is obviously
not correct.
> > > >> Occasionally it will show the correct temperature,
but mostly it
> > > >> shows
> > > >> 85c. I replaced the probe with a new one and am
getting the same
> > > >> thing !
> > > >>
> > > >> Now I must admit I don't totally understand 1-wire
yet.. this is my
> > > >> first proper jump into it. So it could be that I
have set up
> the bus
> > > >> incorrectly ? or what else is likely to cause this
problem ?
> > > >>
> > > >> The probes are wired in series and the farthest one
is only
> about 10
> > > >> meters away.
> > > >>
> > > >> Anyone got any ideas ? Could I just be really
unlucky and have two
> > > >> probes shorting out ?
> > > >>
> > > >> Any help appreciated
> > > >>
> > > >> Marc
> > > >>
> > > >>
> > > >>
> > > >>
> > > >>
> > > >>
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > >
> >
> >
> >
> >
> >
> >
> >
>
>






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