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'[PIC]: DS18S20'
2002\04\08@195842 by Tony Nixon

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Hi all,

I've been putting together a small data logger application that uses 4
of the DS18S20 1 wire temp sensors, a Honeywell humidity sensor and two
electronic scales that I talk to with bit banged RS232 code. I then
relay the results to the PC via the UART, or just store to local I2C
memory for portabillity.

The data sheet says 750mS to get each temp conversion and some people
here want to use the logger with more temp sensors. The trouble is the
acquisition time goes up substantially and you can't really say that the
temps were all logged at exactly X time.

Is there any way around this that anyone knows of.

Assuming someone knows the DS18S20, I was wondering if you could use a
bypass ROM command and start the conversions all together, and then read
individually after just a single 750mS conversion???

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2002\04\08@200434 by Mark Samuels

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I did one application with 4 DS18S20's, and since the temperature change
wasn't all that dynamic, I set up a 1 second interrupt, where I would cycle
through the 4 sensors.  I basically built in a "lag", where at each 1
second interrupt, I'd start a conversion on one sensor, then read the
previous sensor which had gotten it's start conversion command on the
previous 1 second interrupt.
Worked pretty well for me, but like I said, it was a slow enough system
that reading each sensor once every 4 seconds was still ok.

-Mark


At 09:56 AM 4/9/02 +1000, you wrote:
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2002\04\08@203227 by Nick Veys

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Page 9 of the datasheet, Skip Rom command can be followed by Convert T
to perform simulataneous conversions of all devices on the bus.

.....nickKILLspamspam.....veys.com | http://www.veys.com/nick

> {Original Message removed}

2002\04\08@204844 by Donovan Parks

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Hello Tony,

> Assuming someone knows the DS18S20, I was wondering if you could use a
> bypass ROM command and start the conversions all together, and then read
> individually after just a single 750mS conversion???

I have just finished writting some code for the DS18B20.  Basically the same
as the DS18S20, but can give 12-bit of resolution.  As per your question,
take a look at the Skip ROM command on page 9 of the datasheet.  It states
that you can issue a Skip ROM followed by a Convert T command to get all
temp. sensor to simultaneously start temperature conversions.  Of cource,
you then have to read the scratchpad one at a time.  I haven't tried this,
but remembered reading it in the datasheet.  Hope this helps.

Regards,
Donovan Parks

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2002\04\08@205923 by Tony Nixon

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Nick Veys wrote:
>
> Page 9 of the datasheet, Skip Rom command can be followed by Convert T
> to perform simulataneous conversions of all devices on the bus.

Dead right.

I missed that info in my haste to get this thing going.

Many thanks :-)


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2002\04\08@212932 by Tony Nixon

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Nick Veys wrote:
>
> Page 9 of the datasheet, Skip Rom command can be followed by Convert T
> to perform simulataneous conversions of all devices on the bus.

Excellent.

The logger now logs down to 1 second intervals and still should be able
to accommodate more than 4 sensors.


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2002\04\08@213357 by Tony Nixon

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Donovan Parks wrote:

> I have just finished writting some code for the DS18B20.  Basically the same
> as the DS18S20, but can give 12-bit of resolution.  As per your question,
> take a look at the Skip ROM command on page 9 of the datasheet.  It states
> that you can issue a Skip ROM followed by a Convert T command to get all
> temp. sensor to simultaneously start temperature conversions.  Of cource,
> you then have to read the scratchpad one at a time.  I haven't tried this,
> but remembered reading it in the datasheet.  Hope this helps.

Hi Donovan,

I just modified the code and this method works great.

Thanks all for the help.

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2002\04\08@224330 by Nick Veys

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Excellent, glad to see it worked out...

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'[PIC]: DS18S20'
2002\07\15@233152 by Tony Nixon
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Hi all,

Awhile ago I hooked a PIC up to some DS18S20 1 wire temp sensors to
measure air and fluid temps.

The fluid temps work well obviously due to good heat transfer in fluids.

The air temps don't seem to work well at all - ambient air being a bad
heat conductor I suppose.

Does anyone know of any tricks to make these measure air temp.

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2002\07\16@004508 by Kevin Olalde

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> The air temps don't seem to work well at all - ambient air being a bad
> heat conductor I suppose.


Not sure what you mean here, they worked fine for me, though I've never used
them for measuring fluid temps so I can't compare.  I powered the device
directly, instead of using parasitic power, and used routines based on these
found at Peter Anderson's site:

http://www.phanderson.com/PIC/16C84/ds1820/1820_1.html

I found there to be a degree (or two) of inconsistency between the devices, but
they individually gave consistent and accurate results.  What sort problems are
you having?

Kevin

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2002\07\16@005751 by Tony Nixon

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Kevin Olalde wrote:
>
> > The air temps don't seem to work well at all - ambient air being a bad
> > heat conductor I suppose.
>
> Not sure what you mean here, they worked fine for me, though I've never used
> them for measuring fluid temps so I can't compare.  I powered the device
> directly, instead of using parasitic power, and used routines based on these
> found at Peter Anderson's site:
>
> http://www.phanderson.com/PIC/16C84/ds1820/1820_1.html
>
> I found there to be a degree (or two) of inconsistency between the devices, but
> they individually gave consistent and accurate results.  What sort problems are
> you having?
>
> Kevin

I have 4 of the devices connected and working happily with a PIC.

A student is using the devices to measure temperature of moist soil
samples and the ambient air temperature just above the samples.

For calibration, the air temp sensors were placed in an oven at 50C but
only measured 30C, the sensors in fluid at 50C measured very close to
50C.

I have them encased in a small tube of aluminuim with heat sink compound
making sure the sensor is in thermal contact with the casing. I had to
do this to insulate them against moisture.

I will get some more sensors and try using them "naked" in the air to
see if that makes a difference.

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Tony

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2002\07\16@083407 by Eoin Ross

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It does sound like you are not allowing enough time for the sensor's temp to ramp to the
ambient temp
Attaching heat sinks or more material will add to the mass that has to absorb/radiate
heat, therefore making the problem worse.

>>> RemoveMETony.NixonEraseMEspamEraseMEENG.MONASH.EDU.AU 07/16/02 12:55AM >>>
Kevin Olalde wrote:
>
> > The air temps don't seem to work well at all - ambient air being a bad
> > heat conductor I suppose.

I have 4 of the devices connected and working happily with a PIC.

A student is using the devices to measure temperature of moist soil
samples and the ambient air temperature just above the samples.

For calibration, the air temp sensors were placed in an oven at 50C but
only measured 30C, the sensors in fluid at 50C measured very close to
50C.

I have them encased in a small tube of aluminuim with heat sink compound
making sure the sensor is in thermal contact with the casing. I had to
do this to insulate them against moisture.

Tony

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2002\07\16@092921 by Roman Black

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Tony Nixon wrote:
>
> Hi all,
>
> Awhile ago I hooked a PIC up to some DS18S20 1 wire temp sensors to
> measure air and fluid temps.
>
> The fluid temps work well obviously due to good heat transfer in fluids.
>
> The air temps don't seem to work well at all - ambient air being a bad
> heat conductor I suppose.
>
> Does anyone know of any tricks to make these measure air temp.


Have you tried a heatsink?? Those little "flag"
style sinks for TO-92 will probably do the trick. :o)
-Roman

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2002\07\16@094636 by Roman Black

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Eoin Ross wrote:
>
> It does sound like you are not allowing enough time for the sensor's temp to ramp to the
> ambient temp
> Attaching heat sinks or more material will add to the mass that has to absorb/radiate
> heat, therefore making the problem worse.


Now i've recently been demoted to <freshman physics,
but surely a heatsink provides greater thermal coupling
between the air and the device??
-Roman

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2002\07\16@095843 by Eoin Ross

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It does ... but here is an example of what I am getting at.

You have a lump of 25mm steel plate 25mm square
Also you have a 1 mm steel sheet 25 mm square
One side of each sheet is exposed to a temp change.

Which sheet will have the "unexposed" side track the temperature change the closest?
It should be the thinner sheet as there is less mass the energy has to travel through.


>>> RemoveMEfastvidspam_OUTspamKILLspamEZY.NET.AU 07/16/02 09:43AM >>>
Eoin Ross wrote:
>
> It does sound like you are not allowing enough time for the sensor's temp to ramp to the
> ambient temp
> Attaching heat sinks or more material will add to the mass that has to absorb/radiate
> heat, therefore making the problem worse.


Now i've recently been demoted to <freshman physics,
but surely a heatsink provides greater thermal coupling
between the air and the device??
-Roman

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2002\07\16@100845 by john

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as mick jagger sang...... paint it black ;)

On Tuesday 16 July 2002 03:58 pm, you wrote:
{Quote hidden}

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Thank-you for your time.

John Ward

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2002\07\16@103434 by Roman Black

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Eoin Ross wrote:
>
> It does ... but here is an example of what I am getting at.
>
> You have a lump of 25mm steel plate 25mm square
> Also you have a 1 mm steel sheet 25 mm square
> One side of each sheet is exposed to a temp change.
>
> Which sheet will have the "unexposed" side track the temperature change the closest?
> It should be the thinner sheet as there is less mass the energy has to travel through.


Yes but a sensor on a heatsink is in contact with
MORE total air, and the air temp will have a greater
effect on device temp. The device will always stabilise
at air temp (assume zero self heating) but with the
heatsink it will be *faster* affected by air temp, and
will follow the air temp with less time lag. Besides,
i'm cheating, i've repaired commercial devices that
had heatsink like things on the thermal sensors. :o)
-Roman

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2002\07\16@115050 by Steven Allard

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Glasshouse thermostats use fan's to blow air across the sensor to improve response times.

Roman Black wrote:

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2002\07\18@053324 by Vasile Surducan

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> > Now i've recently been demoted to <freshman physics,
> > but surely a heatsink provides greater thermal coupling
> > between the air and the device??
> > -Roman


   Absolutely, is the reversed effect of cooling the power transistors
with a large surface heatsink.
And will be better if the air is saturated with 30%HCl + 30%HN03 + 30%
H2SO4  :-) The DS will screeeeam nice.

Vasile

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2002\07\18@090547 by Bob Ammerman

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I would expect the ideal situation for quick response would be a
very-low-mass, very-large-surface-area heatsink.

Bob Ammerman
RAm Systems

{Original Message removed}

2002\07\18@145839 by Peter L. Peres

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On Thu, 18 Jul 2002, Bob Ammerman wrote:

>I would expect the ideal situation for quick response would be a
>very-low-mass, very-large-surface-area heatsink.

Very low *thermal* mass ? I do not know which material has this, but I
suspect Aluminium comes close. Copper does not (high thermal mass). There
could be something better.

Peter

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2002\07\19@030818 by Vasile Surducan

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On Thu, 18 Jul 2002, Peter L. Peres wrote:

> On Thu, 18 Jul 2002, Bob Ammerman wrote:
>
> >I would expect the ideal situation for quick response would be a
> >very-low-mass, very-large-surface-area heatsink.
>
> Very low *thermal* mass ? I do not know which material has this, but I
> suspect Aluminium comes close. Copper does not (high thermal mass). There
> could be something better.


 aluminium sponge maybe ? I have somewhere a sample on my desk...

Vasile

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2002\07\19@040402 by dr. Imre Bartfai

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+-----------------------------------------------------------------------+
Hi,

I think it is very simple to create similar circumstances: take a Venus
trip!

Imre

On Thu, 18 Jul 2002, Vasile Surducan wrote:

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2002\07\19@041120 by Vasile Surducan

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Too expensive Imre,
Take the train to Kolosvari and I can simulate this atmosfere for you !
;-))

regards,
Vasile
http://www.geocities.com/vsurducan


On Fri, 19 Jul 2002, dr. Imre Bartfai wrote:

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