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'Detecting temperature at a point'
1995\11\27@163221 by Gerry Smith

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I'm trying to use the  PIC processors to detect temperature at a point.
Unlike area or room thermometers, I want to take the temperature a spefic
point (eg. water or body temperature).  Would anyone know of any sensors
that would be suited for this?  I have thought of themiresistors and
temperature ICs.  Are there anymore or better ones?  If not, which is better?
Thanks in advance.

1995\11\28@040950 by mike

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In message <spam_OUT9511280206.aa02498TakeThisOuTspampunt-4.mail.demon.net> .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
writes:
> I'm trying to use the  PIC processors to detect temperature at a point.
> Unlike area or room thermometers, I want to take the temperature a spefic
> point (eg. water or body temperature).  Would anyone know of any sensors
> that would be suited for this?  I have thought of themiresistors and
> temperature ICs.  Are there anymore or better ones?  If not, which is better?
> Thanks in advance.
>
Hi,

You could try the Dallas Semiconductor DS1820 - a 3 lead device
that does the temp -> digital conversion for you.

It uses just one i/o pin for communication, requires no external
components and measures temperatures in the range -55 degC to
+125 degC in 0.5 degC increments. It also has under and over
temperature alarms.

Hope this helps,

Mike Watson
--
Mayes uk

1995\11\28@084337 by Jack Coats

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----- Begin Included Message -----

From: Gerry Smith <LIUKBspamKILLspamKIRK.NORTHERNC.ON.CA>
Subject:      Detecting temperature at a point

I'm trying to use the  PIC processors to detect temperature at a point.
Unlike area or room thermometers, I want to take the temperature a spefic
point (eg. water or body temperature).  Would anyone know of any sensors
that would be suited for this?  I have thought of themiresistors and
temperature ICs.  Are there anymore or better ones?  If not, which is better?
Thanks in advance.

----- End Included Message -----

The devices you mentioned really only take temps at the point where the
sensor is, not of an area.  You might try attaching your device
directly to the object you want to monitor, and insulate from heat
coming from other directions to get better readings.

If there are more (cheap?) sensors, I am sure several of us are interested!

1995\11\28@135249 by Bill Cornutt

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----------
{Quote hidden}

The DS1620 (available from Jamco for $7.00 US) is also available
with a rhree wire communicationa line.

I have played with a cheep thermister that I hooked up to a 555
ic.  I hooked the thermister in the "charging" circuit of a 555
and put a diode in series with it so that it will have no effect
on the discharge time.  Then I used the pc to count the on time
and off time of the 555 output (in the free runing mode).  The
tempreture measument is made by taking the ratio of the "on" time
to the "off" time.  This can be used to determin very small changes
in tempreture.  Because of not being in sync with the 555 and the
various interupts on the pc, the counts do vary.  But averaging
a few of the counts will smooth out the reading (and slow the
sampling rate).

In the PIC books there is an example of using some i/o pins
to read a variable resistor (which is what a thermister is).
I do not remember how it is used exactly, but here is a susgestion.

The series circuit consists of three componets.  The thermister, a
resistor (to limit current through PIC  pins) and a capicator.
The other end of the capicator is connected to ground.  The other
end of the thermistor is connected to a pic i/o pin.  A second
PIC i/o pin is connected to the junction of the thermister/resistor.

The circuit works by charging the capacator through the thermister
and measuring the time, then discharging the capacator, and doing
it again.

The cap is discharged by tristating the i/o pin hooked to the
thermister and outputting a low (ground) on the pin hooked
to the thermister/resistor junction for a good length of time.
Then to start the reading, the junction pin is set to input
and the thermister pin is set to output a high (+5v).  Now
the cap is charging through the thermister.  A count of the time
it takes for the voltage on the junction pin to raise to the point
where it is read as a high input by the PIC.  This time is the
tempreature.

Just be sure you have the resistor in the circuit to limit any
current (assuming 5v) to a safe level for the PIC pins.

To get more fancy, could you use a ir device?  A ir transistor?
Would it go in one of the above circuits as a current device?

Or could it be hooked up to the control pin of a free running 555
to change frequency of the 555's output.  Then you could just point
the device at something and get its tempreature.

If you use some crazy scheme to measure tempreture, it may be wise
to also get a Dallas Semiconductor device that is calibrated and
use it to reference the readings of your device.  Take some salt or
cooking oul and heat it in the micro wave.  Then stick both devices
in the stuff and have the computer record the readings from each as
it cools to room tempreature,  Then put the stuff in the freezer
for a while and repeat the reacordings as it warms to room tempreature.
Then you will have a good conversion table.

Bill C.

1995\11\28@183035 by Andrew Warren
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Gerry Smith <LIUKBspamspam_OUTKIRK.NORTHERNC.ON.CA> wrote:

> I'm trying to use the  PIC processors to detect temperature at a
> point. Unlike area or room thermometers, I want to take the
> temperature a spefic point (eg. water or body temperature).  Would
> anyone know of any sensors that would be suited for this?

       It sounds as though you want to measure temperature at a distance.
       Is that true?  If so, there are plenty of manufacturers of infrared
       pyrometers that'll do exactly what you want.  I had one about 8 years
       ago that would display a person's skin temperature from across the
       room... They're real cool.

       I don't know, offhand, who makes the sensors; you may want to try
       calling Omega Engineering at 800 826-6342.  They make a whole line of
       infrared thermometers and can probably give you some information
       about the raw sensors.

       -Andy

Andrew Warren - @spam@fastfwdKILLspamspamix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geopages.com/SiliconValley/2499

1995\11\28@184303 by Ben L Wirz

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       Eltec Instrment, Inc. (1-800-874-7780) makes pyroelectric detectors
and I agree they are really cool!  I have been researching them for use
in home robotics to differeniate humans from other inanimate objects.
I've been writing a research paper for one of my classes that I will
probably put on my WEB page in a couple weeks if anyone is interested.

Ben

Ben Wirz                Check out My Home Page for Great Deals on Bulk
                       Buy Electronics (LMD 18200 H Bridge and PIC 16C84)
KILLspamblw2KILLspamspamcec.wustl.edu      http://cec.wustl.edu/~blw2/index.html

On Tue, 28 Nov 1995, Andrew Warren wrote:

{Quote hidden}

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