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PICList Thread
'Help on temperature sensor'
1999\10\06@121144 by Octavio Nogueira

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I'm developing a temperature controller with two sensors,
I'm using a 16F877 and I'm almost finished, the only problem
is the temperature sensor.
- I though of using thermostat, but I will have to calibrate
each unit.
- I though of using Dallas DS1820 but they are expensive
- I though of using Dallas DS1822, the price is ok the not
the availability.
Any other though?
The range is from 50F to 150F and need to be cheap.

Friendly Regards

Octavio Nogueira
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1999\10\06@124314 by Robert A. LaBudde

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At 02:00 PM 10/6/99 -0300, Octavio wrote:
>I'm developing a temperature controller with two sensors,
>I'm using a 16F877 and I'm almost finished, the only problem
>is the temperature sensor.
>- I though of using thermostat, but I will have to calibrate
>each unit.
>- I though of using Dallas DS1820 but they are expensive
>- I though of using Dallas DS1822, the price is ok the not
>the availability.
>Any other though?
>The range is from 50F to 150F and need to be cheap.

1. The LM34 (F) or LM35 (C) is very nice (10 mV per F or C). Cost about $1.

2. You could use a thermistor in a voltage divider circuit. Cost about $.50
for the thermistor. You'd have to calibrate it and program a linearization
routine.

3. You could construct a LM34/35 sensor out of a transistor wired as a
diode. You'd have to calibrate it (~ 1 mV per C?). Cost $.06.

4. You can use a piece of thermocouple wire (type T is easiest). You'd have
to have an amplifier with a gain ~ 200. Cost of the wire $.01 for a 1 cm piece.

5. You can twist a copper and iron or other metal wire together to make a
thermocouple. You'd have to calibrate it.

Personally, I think the LM34/35 is the best solution to this kind of
problem, so long as you have an ADC channel available. It's cheap,
accurate, small and calibrated. The second best solution would be to make a
transistor sensor and calibrate it. It you have to do it with a digital
pin, thermistors are easier.


================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: .....ralKILLspamspam@spam@lcfltd.com
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1999\10\06@125057 by Marcelo Yamamoto

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D uma olhada no AN512 da Microchip.


Marcelo Y.
m_yamamotospamKILLspamuol.com.br



{Quote hidden}

1999\10\06@125100 by Marcelo Yamamoto

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Otavio wrote:

>I'm developing a temperature controller with two sensors,
>I'm using a 16F877 and I'm almost finished, the only problem
>is the temperature sensor.
>- I though of using thermostat, but I will have to calibrate
>each unit.

Take a look at AN512 at Microchip.

>- I though of using Dallas DS1820 but they are expensive
>- I though of using Dallas DS1822, the price is ok the not
>the availability.

I use a termistor supplied by US Sensor. 10k curve J, $0.10 US each.
Take a look. http://www.ussensor.com
and I read it as a cap charge time.

Marcelo Y.
EraseMEm_yamamotospam_OUTspamTakeThisOuTuol.com.br

1999\10\06@155032 by Harold M Hallikainen

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On Wed, 6 Oct 1999 09:24:31 -0700 Dave Johnson <djohnsonspamspam_OUTSIRIUS.COM>
writes:
>Octavio Nogueira wrote:
>
>>Any other though?
>>The range is from 50F to 150F and need to be cheap.
>It appears you want direct-to-digital sensors, right? That really
>limits
>the choices.
>
>If an analopg output is suitable, you might look at the Analog Devices
>TMP36, range is -40 to +125 deg C, and they're under a dollar in
>quantity.
>
>Dave Johnson


       Also, if analog is ok, see National LM35DZ and similar chips.

Harold


Harold Hallikainen
@spam@haroldKILLspamspamhallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

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1999\10\06@194405 by Richard Prosser

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National Semis produce a range of sensors of which the LM335 is an example
(to give you a starting point).

It depends on your accuracy requirement whether or not you need to calibrate
them

The LM335 produces 10mV per degree K but other versions will produce degrees
Rankine or F I think.

Calibration is a single pot so isn't too hard if you've got a known, stable
temperature.

I think their cheapest sensor (LM85 ?? - calibrated in degrees C) is about
$NZ0.85


Richard P

> {Original Message removed}

1999\10\07@165509 by Stefan Wojtowycz

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Have you thought of a LM335Z. This ranges from 0 to 100 C. It has an output
of 10 mV per degree Kelvin. Units cost approx.#1.00 sterling.
 Stefan.
{Original Message removed}

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