Thank you for clarifying Paul. Collisions checked only with a simple CRC
seemed a bit unreliable to me. As you explained it, it is a much more
robust than I thought.
On Wed, Apr 10, 2013 at 12:25 PM, Paul Alfille <paul.alfi...@gmail.com>wrote:
> 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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