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'[PICLIST] temp sensors cable length'
2001\07\12@143337 by Pedro Drummond

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Hi friends.

From personal experience, what should be the maximum distance one can read a Dallas 1620 or 1820 from ? I mean serial signals directly, without RS 232, 485, etc.


TIA,

Pedro.

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2001\07\12@145026 by Douglas Butler

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It all depends on the environment.  I have one product that sends 1200
baud TTL level serial data 400 meters.  It is through coax under
seawater so there is virtually no interference.  If I wrap the coax
around a running CRT I get all sorts of transmission errors.
What type of wire are you looking to use and where will it run?

Sherpa Doug

> {Original Message removed}

'[PICLIST] [OT] Re: temp sensors cable length'
2001\07\12@150444 by Pedro Drummond

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It will run up to my house's roof, to measure water temp on pipes that are
heated by sun panels. Maybe 15 to 20 meters total length, at the most.

I was considering twisted pair...



----- Original Message -----
From: Douglas Butler <spam_OUTdbutlerTakeThisOuTspamIMETRIX.COM>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Thursday, July 12, 2001 3:43 PM
Subject: Re: temp sensors cable length


> It all depends on the environment.  I have one product that sends 1200
> baud TTL level serial data 400 meters.  It is through coax under
> seawater so there is virtually no interference.  If I wrap the coax
> around a running CRT I get all sorts of transmission errors.
> What type of wire are you looking to use and where will it run?
>
> Sherpa Doug
>
> > {Original Message removed}

2001\07\12@231309 by Patrick J

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You might want to check out something called "SmartTemp"
It sends the temp value as a pulsetrain all you haveto do is to check the
ratio between low-high and the % is linear to the temp. They even supply
PIC asm demo.
Extremly simple principle : Just sample say 1000 samples and count all
high and all lows u get. That will give you the ratio !

The senssor itself is TO92 (very small, looks like a small transistor) and
it comes lasertrimmed to better than 0.5-1 degree celsious depending on
which casing you choose. Cable lenght can be very long.

If this seems interesting I can dig out some old ASM I did way back to
test it. And some more detailed info.

/PJ

From: "Pedro Drummond"
> It will run up to my house's roof, to measure water temp on pipes that are
> heated by sun panels. Maybe 15 to 20 meters total length, at the most.

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2001\07\13@010211 by Brent Brown

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> You might want to check out something called "SmartTemp"
> It sends the temp value as a pulsetrain all you haveto do is to check the
> ratio between low-high and the % is linear to the temp. They even supply
> PIC asm demo.
> Extremly simple principle : Just sample say 1000 samples and count all
> high and all lows u get. That will give you the ratio !
>
> The senssor itself is TO92 (very small, looks like a small transistor) and
> it comes lasertrimmed to better than 0.5-1 degree celsious depending on
> which casing you choose. Cable lenght can be very long.
>
> If this seems interesting I can dig out some old ASM I did way back to
> test it. And some more detailed info.

Yes they are very nice, I used them in a recent project. Think they
were called Smartec.

It seems strange but in my case the cable length did adversely
affect accuracy. As cable length (capacitance) increases the
waveform rounds off on the edges. This was fed straight into a PIC
input and I think the non-symetrical nature of the Vin(LOW) and
Vin(HIGH) specs messed things up as the . It was OK up to about
10m of standard 6 core flat telephone cable, after that the error was
too great.

The solution would probably be to use a schmitt trigger before the
input to the PIC, or a comparator, to give better defined threshold
points. I even thought of adding a driver to the temp sensor device
(something like a single gate inverter) to help with long cables, and
some power supply filtering might help too. Hope this gives you
some ideas on what to watch out for.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  brent.brownspamKILLspamclear.net.nz

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2001\07\13@181715 by Patrick J

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You might want to check out something called "SmartTemp" sensor by Smartec
It sends the temp value coded as a pulse-with-modulated signal. All you haveto
do is to check the ratio between low-high and the % is linear to the temp.
They even supply PIC asm demo.
Extremly simple principle : Just sample say 1000 times and count all
high and all lows u get. That will give you the ratio !

The senssor itself is TO18, TO92, TO220 or SO8L and it comes lasertrimmed.
Around 0.5-1 degree celsius depending on which casing you choose. Cable
lenght can be very long.

If this seems interesting I can dig out some old ASM I did way back to
test it. And some more detailed info.

/PJ

From: "Pedro Drummond"
> It will run up to my house's roof, to measure water temp on pipes that are
> heated by sun panels. Maybe 15 to 20 meters total length, at the most.

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