The 85C readings are temperature measurement errors from the chip, probably
due to marginal power. Temperature "conversions" take a fair amount of
power.
OWFS automatically retries 85C 3 times. The prior suggestions of ensuring a
better voltage supply, or just ignoring the bad readings, are probably the
best option.
As a matter of accuracy, the collisions are true for ethernet (at least
prior to switches everywhere) but not 1-wire. The collision protocol for
1-wire is a very clever scheme (since each slave can only change a 1 to a 0
on the line) of enumerating the chip addresses by looking for "and" and
"or" logical responses in the address query, then addressing the specific
chip for further communication.
Paul Alfille
On Wed, Apr 10, 2013 at 1:06 PM, Rob Kapteyn <robkapt...@gmail.com> wrote:
> I do almost the same thing with a Raspberry Pi and I get the same errors
> with the same frequency. I'm new to OWFS, but I'm fairly sure that those
> are just normal 1-wire "collisions". When the master requests data from
> the bus, each sensor waits a random period of time and then sends its
> ID+data. Occasionally, two sensors just happen to send at the same time.
> My python script just tries again when there is a CRC error.
>
> BTW, I don't use a DS2482 master. I just drive the data bus from GPIO
> pin4.
> OWFS is built into Raspbian and already configured for pin 4.
> Just load three modules to enable it:
> sudo modprobe wire
> sudo modprobe w1_gpio
> sudo modprobe w1_therm
>
>
>
> On Mon, Apr 8, 2013 at 3:49 PM, <s...@gmx-topmail.de> wrote:
>
>>
>> Hi,
>> I use owfs on a raspberry pi with ds2482 and ten ds18s20 on about 10 m
>> cable.
>> i read the temperatures from the mounted file system with a python script
>> every minute.
>> so about 60x60x10 measurement values a day. From time to time I get read
>> errors on the sensors .
>> they give a temperature of 85 deg. This happens about 10 to 15 times a
>> day. So not often, and normally the bus works great. But how can I fix
>> this? What's the problem? Conversion time?
>> thanks for any help
>>
>>
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