This power failure mode is similar to the battery-powered devices such as the
ds1923 and is noted in the datasheet. Devices self- report but data is
nonsensical.
Colin
> On Nov 18, 2013, at 23:16, Jan Chrillesen <[email protected]> wrote:
>
> Hi Mick,
>
> Thanks for the reply. I think I have the the source of the issue - it seems
> to be related to the quality of the power to the 1-wire bus. Last night I
> tried different things - soldering everything together, instead of using a
> breadboard and connecting to a known-good bus with 10 devices. The result was
> still the same - all devices were recognized by owfs, but the temperature was
> 127 degrees on all 10 DS18B20's.
> Then I changed the power supply to my Beaglebone from being powered over USB
> from my Mac, to a standalone 5V DC/2A power supply, and the problem went away
>
> The DS2483 is powered from the 3.3V and 5V VDD, from the Beaglone Black -
> this means that the 1-wire bus is also powered from the same 5V source as the
> Beagleboard
>
> I didn't put a scope on the 5V supply, so I don't know if the level was too
> low, or there's some noise on the 5V supply.
>
> However, it seems it's possible to power the 1-wire bus in such a way, that
> the devices responds correctly to queries from the bus master, but fails to
> convert the measured temperature
>
> - JAN
> Tændt 8. nov. 2013 at 17.38.56, Mick Sulley ([email protected]) Skrev:
>
>> Apologies for not replying before, just noticed the post again.
>>
>> The problem just went away, so I have no idea what caused or cured it.
>> Sorry I can't be more help
>>
>> Mick
>>
>>
>> On 22/10/13 07:47, Jan Chrillesen wrote:
>> > On Thu, 25 Apr 2013, Mick Sulley <[email protected]> wrote:
>> >
>> >> No I have never changed it, just leave it as Centigrade. The strange
>> >> thing is that most of the readings are OK, around 19, 20 or so, but then
>> >> these odd ones at 127
>> >>
>> >> I will continue to monitor!
>> > (Replying to an old posting)
>> >
>> > Did you ever find a solution for this?
>> >
>> > I have just set up a Beaglebone Black with DS2483 and a single DS18B20,
>> > using owfs 2.9.1, and see the same behaviour (temperature always
>> > 127.938). I haven't yet tried to add more sensors
>> >
>> > - Jan
>>
>>
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> Jan Chrillesen
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