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Roberto Spadim | 1 Mar 2012 02:31
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know problem with ds18b20

hi guys, i'm having a lot of problem with ds18b20 and 85 degree reads
what are every body doing when this occur?
today i read to times when this occur, and if it's 85 em both i allow 85 degree
anyone know another good solution?

--

-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial

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Eloy Paris | 1 Mar 2012 03:07

Re: know problem with ds18b20

Hi Roberto,

On 02/29/2012 08:31 PM, Roberto Spadim wrote:

> hi guys, i'm having a lot of problem with ds18b20 and 85 degree reads
> what are every body doing when this occur?
> today i read to times when this occur, and if it's 85 em both i allow 85 degree
> anyone know another good solution?

If parasitic powered make sure that Vdd is connected to ground instead 
of leaving it floating. If they are being powered then I am afraid I 
don't have a good suggestion :-(

Cheers,

Eloy Paris.-

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Roberto Spadim | 1 Mar 2012 03:12
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Re: know problem with ds18b20

yes hehe my is the second, i connect 5v, 0v and owbus
does ds18b20 have a crc or another feature that shows the reset status
or something else? i could check for example....
read 85 degree
read the crc value (or another reset value)
start of infinite loop:
   read 85 degree again
   read the crc value (or another reset value)
if crc value = reset value, loop, else good read

i don't know if exists a reset counter or something like it in
ds18b20, does anyone know?

Em 29 de fevereiro de 2012 23:07, Eloy Paris <peloy <at> chapus.net> escreveu:
> Hi Roberto,
>
>
> On 02/29/2012 08:31 PM, Roberto Spadim wrote:
>
>> hi guys, i'm having a lot of problem with ds18b20 and 85 degree reads
>> what are every body doing when this occur?
>> today i read to times when this occur, and if it's 85 em both i allow 85
>> degree
>> anyone know another good solution?
>
>
> If parasitic powered make sure that Vdd is connected to ground instead of
> leaving it floating. If they are being powered then I am afraid I don't have
> a good suggestion :-(
>
(Continue reading)

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Eric Vickery | 1 Mar 2012 03:17

Re: know problem with ds18b20

Even if they are powered you have to make sure you are waiting long enough before taking a reading 
after a temperature convert. At 12bits the DS18B20 takes as long as the DS18S20 (around 750mS).

On 2/29/2012 8:12 PM, Roberto Spadim wrote:
> yes hehe my is the second, i connect 5v, 0v and owbus
> does ds18b20 have a crc or another feature that shows the reset status
> or something else? i could check for example....
> read 85 degree
> read the crc value (or another reset value)
> start of infinite loop:
>     read 85 degree again
>     read the crc value (or another reset value)
> if crc value = reset value, loop, else good read
>
> i don't know if exists a reset counter or something like it in
> ds18b20, does anyone know?
>
>
> Em 29 de fevereiro de 2012 23:07, Eloy Paris<peloy <at> chapus.net>  escreveu:
>> Hi Roberto,
>>
>>
>> On 02/29/2012 08:31 PM, Roberto Spadim wrote:
>>
>>> hi guys, i'm having a lot of problem with ds18b20 and 85 degree reads
>>> what are every body doing when this occur?
>>> today i read to times when this occur, and if it's 85 em both i allow 85
>>> degree
>>> anyone know another good solution?
>>
(Continue reading)

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Roberto Spadim | 1 Mar 2012 03:21
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Re: know problem with ds18b20

i was reading datasheet..
http://datasheets.maxim-ic.com/en/ds/DS18B20.pdf

there's a eeprom memory portion that is copied when device startup
could we set for example 0xff at this position
and after setting , set the current value to 0x00 ?
when device is running fine value is 0x00
when device is reseted it's get 0xff
i don't know if this work since memory value is:
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0 R1 R0 1 1 1 1 1

r1,r0 = data resolution
but maybe this could work? the 1111 value could be changed?

Em 29 de fevereiro de 2012 23:12, Roberto Spadim
<roberto <at> spadim.com.br> escreveu:
> yes hehe my is the second, i connect 5v, 0v and owbus
> does ds18b20 have a crc or another feature that shows the reset status
> or something else? i could check for example....
> read 85 degree
> read the crc value (or another reset value)
> start of infinite loop:
>   read 85 degree again
>   read the crc value (or another reset value)
> if crc value = reset value, loop, else good read
>
> i don't know if exists a reset counter or something like it in
> ds18b20, does anyone know?
>
(Continue reading)

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Roberto Spadim | 1 Mar 2012 03:30
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Re: know problem with ds18b20

yes, well i think owfs is doing 1second wait time of pullup with
serial-onewire dallas converter (i don't remeber it exactly i think
it's ds2480b)

the question is... it's works but sometimes it work wrongly
i was thinking something like...

write alarm high temperature of user value to eeprom and to current memory
change eeprom to uservalue+1
when device is reseted eeprom=current memory
this time we know that device reseted and the 85 value is wrong

it's ugly but since ds18b20 don't have a user bit to save information
at eeprom... i think it's a solution (maybe not a good one) that
remove 85 degree error

Em 29 de fevereiro de 2012 23:17, Eric Vickery
<ericvic <at> hobby-boards.com> escreveu:
> Even if they are powered you have to make sure you are waiting long enough before taking a reading
> after a temperature convert. At 12bits the DS18B20 takes as long as the DS18S20 (around 750mS).
>
> On 2/29/2012 8:12 PM, Roberto Spadim wrote:
>> yes hehe my is the second, i connect 5v, 0v and owbus
>> does ds18b20 have a crc or another feature that shows the reset status
>> or something else? i could check for example....
>> read 85 degree
>> read the crc value (or another reset value)
>> start of infinite loop:
>>     read 85 degree again
>>     read the crc value (or another reset value)
(Continue reading)

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Roberto Spadim | 1 Mar 2012 03:33
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Re: know problem with ds18b20

maybe the configuration eeprom register could help...
when we read with 9 bits we could change eeprom to 10 bits, set
current to 9bits execute conversion algorithm
the eeprom configuration never could be = current conversion bit, or
we know that device was reseted and the 85 degree is wrong

there's a way to read eeprom value, and the current value? or ds18X20
don't allow this?

Em 29 de fevereiro de 2012 23:30, Roberto Spadim
<roberto <at> spadim.com.br> escreveu:
> yes, well i think owfs is doing 1second wait time of pullup with
> serial-onewire dallas converter (i don't remeber it exactly i think
> it's ds2480b)
>
> the question is... it's works but sometimes it work wrongly
> i was thinking something like...
>
> write alarm high temperature of user value to eeprom and to current memory
> change eeprom to uservalue+1
> when device is reseted eeprom=current memory
> this time we know that device reseted and the 85 value is wrong
>
> it's ugly but since ds18b20 don't have a user bit to save information
> at eeprom... i think it's a solution (maybe not a good one) that
> remove 85 degree error
>
>
> Em 29 de fevereiro de 2012 23:17, Eric Vickery
> <ericvic <at> hobby-boards.com> escreveu:
(Continue reading)

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Roberto Spadim | 1 Mar 2012 03:35
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Re: know problem with ds18b20

ds18s20 don't allow this... but ds18b20 could work :D what you think?

Em 29 de fevereiro de 2012 23:33, Roberto Spadim
<roberto <at> spadim.com.br> escreveu:
> maybe the configuration eeprom register could help...
> when we read with 9 bits we could change eeprom to 10 bits, set
> current to 9bits execute conversion algorithm
> the eeprom configuration never could be = current conversion bit, or
> we know that device was reseted and the 85 degree is wrong
>
> there's a way to read eeprom value, and the current value? or ds18X20
> don't allow this?
>
> Em 29 de fevereiro de 2012 23:30, Roberto Spadim
> <roberto <at> spadim.com.br> escreveu:
>> yes, well i think owfs is doing 1second wait time of pullup with
>> serial-onewire dallas converter (i don't remeber it exactly i think
>> it's ds2480b)
>>
>> the question is... it's works but sometimes it work wrongly
>> i was thinking something like...
>>
>> write alarm high temperature of user value to eeprom and to current memory
>> change eeprom to uservalue+1
>> when device is reseted eeprom=current memory
>> this time we know that device reseted and the 85 value is wrong
>>
>> it's ugly but since ds18b20 don't have a user bit to save information
>> at eeprom... i think it's a solution (maybe not a good one) that
>> remove 85 degree error
(Continue reading)

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Roberto Spadim | 1 Mar 2012 03:44
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Re: know problem with ds18b20

the new logic could be:

start loop:
start conversion
read scratch
if we don't have a 85degree exit loop
else, we got a 85 degree...
    read rom
    check if rom and scratch value are =, if not exit loop (we have a
real 85 degree)

     if they are "=" we have a reseted device... :(
         change current temphigh value to eprom -1 (may be we may need
to use temp low +1, if temp high = the highest value....)
         return to start

------------------------------------------------------------------------------
Virtualization & Cloud Management Using Capacity Planning
Cloud computing makes use of virtualization - but cloud computing 
also focuses on allowing computing to be delivered as a service.
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Roberto Spadim | 1 Mar 2012 04:05
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Re: know problem with ds18b20

maybe if we include a
ROM/
directory and a
SCRATCH/
directory
one with information from rom and other with informations from scratch

could help the owfs client to make a reset logic, and don't change the
owserver logic :)
this could be very very better

Em 29 de fevereiro de 2012 23:44, Roberto Spadim
<roberto <at> spadim.com.br> escreveu:
> the new logic could be:
>
> start loop:
> start conversion
> read scratch
> if we don't have a 85degree exit loop
> else, we got a 85 degree...
>    read rom
>    check if rom and scratch value are =, if not exit loop (we have a
> real 85 degree)
>
>     if they are "=" we have a reseted device... :(
>         change current temphigh value to eprom -1 (may be we may need
> to use temp low +1, if temp high = the highest value....)
>         return to start

--

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(Continue reading)

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