Re: Re: 1-Wire Headache

[Marc Fuller <groups@xxxxxxxxxxxxxxxxxx>]

OK, this has got very weird.

So I read somewhere that the VDD should be crossed to GND. This can be
done at the sensor or at the PCB. So as a test I moved VDD to ground at
the last sensor and hey presto it started working.

To make things a bit neater I put it back to the VDD pin with the
thought of moving the VDD cable to CNG at the PCB. Once this was done,
the last sensor stopped working again (all others were still working).

Strange I thought, so I lwft VDD to GND at the pcb but almost linked VDD
to GND at the sensor.. and what do you know, all working.

It looks to me that the VDD cable may have a break in it between sensor
2 and 3.

Oh well, working now :D

Cheers

Marc

Jon Payne wrote:
>
> 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
> <mailto:groups%40serenitymeadow.com>>
> To: ukha_d@xxxxxxx <mailto:ukha_d%40yahoogroups.com>
> 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>
> <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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