Body temaprature measurment!

UroBoros · Feb 15, 2005

ds18s20 incubator

Hai
I want to do a clinical thermometer using microcontrollers.
Which is the best temprature sensor for my purpose?
thanks
picstudent

IanP · Feb 15, 2005

One of the best temperature sensors is PT100 platinium resitor.
It will give you graet linearity and the resistance-temperature relationship is +0.385Ω/1°C.
http://www.lanzo.se/applications/pt100.html
You can build bridge amplifier or precision current source and 12-16bit ADC..

Also here some hints on how to measure temperature:
http://www.capgo.com/Resources/Temperature/TempHome/TempMeasurement.html

TinkerDJ · Feb 15, 2005

Here's a schematic and hex code for a pic temp sensor. I'm building a pic temp display circuit but mine needs to read a thermocouple and be able to get upto 1000C.

**broken link removed**

Hope it helps. Oh and you can get the maxim chips as samples.

masoudk_81 · Feb 15, 2005

Hi

you can use SMT160 for microcontrollers that have or have not
A/D converter, and LM35 for the microcntrollers witch have A/D
converter or by means of external A/D. they are both calibrated. SMT160
uses dutyCycle for showing temprature and LM35 uses voltage change.
i have attached an application note for dutycycle measurement here.

catalogs are appended.

masoud

please do not upload files that are available on the net, post a link instead

attachment lm35dz.pdf removed
**broken link removed**

appsmt01.pdf removed
http://www.smartec.nl/pdf/appsmt01.pdf

dssmt16030.pdf removed
**broken link removed**

C-Man

UroBoros · Feb 15, 2005

Hai
I have done a prototype using LM35. But I am not getting good resolution. I have used the built in ADC of PIC16F877 in 10bit mode.I have used a VRef of 3volts .But the value seems to be not stable. Is it possible to derive 0.2C resolution using LM35. datasheet says 10mV/C.Is the change of that 10mV within 1degreeC is lenier?
Thanks for all the links and info.
thanks again
Picstudent

IanP · Feb 15, 2005

Unfortunatelly no.
With 35 temperature sensor you will be somewhere around 1° if lucky.
That was the reason I suggested the PT100 .. reapitibility, stability, ++more ..

gidimiz · Feb 15, 2005

Hi,

With the LM35 you are not getting a stable response because your Vout from it is not stable.
You will have to use a resistor and Cap and a scopt to make a stable reading.
In the datasheet you have few ciruits that show you what is the best way for you to connect it to the ADC.
I am using it with an MCU and it works fine.

Good luck.

Fragrance · Feb 15, 2005

Picstudent said:
Hai
I have done a prototype using LM35. But I am not getting good resolution. I have used the built in ADC of PIC16F877 in 10bit mode.I have used a VRef of 3volts .But the value seems to be not stable. Is it possible to derive 0.2C resolution using LM35. datasheet says 10mV/C.Is the change of that 10mV within 1degreeC is lenier?
Thanks for all the links and info.
thanks again
Picstudent

if you just want to measure body temprature like as in baby incubator the best solution with 0.01 degree accuracy used IN4148 diode as sensor i have posted a classic signal conditioner circuit for this in hobby section. i have built this for using with water bath for medical purpose

jojokatada · Feb 16, 2005

did anyone try using maxim DS18S20 digital thermometer sensor?

glenjoy · Feb 16, 2005

I haven't yet tried the DS18S20 but I am planning to do a board for it.

TinkerDJ · Feb 16, 2005

For those that haven't gone through maxim's appnotes. Very nice selection of temp and other appnotes for alot of there chips.

**broken link removed**

One of the designs is down to 0.1°C. The code they have with this one is for 8051 though.

Nick C. · Feb 16, 2005

I don't think that the LM3x or DS1820 are going to give
you the accuracy you need (very small range of normal
body temperature). Maybe look into thermocouples and
chips such as AD595 and MAX6674. Another quick and
dirty option is to hack a cheap digital thermometer.

Nick

UroBoros · Feb 16, 2005

Nick C. said:
Another quick and
dirty option is to h@ck a cheap digital thermometer.

Nick

Hai
I am impressed by that idea .Will look into that.
but without details how can we locate the point from which we can tap the data?
Thanks to all

Picstudent

glenjoy · Feb 16, 2005

Digital thermometer always has a sensor in it for getting the temperature, the importance of the sensor on a commercial digital thermometer is maybe its accuracy and resolution if you will try to hack an expensive one.

I guess the cheap types uses only thermistor.

I'll go with either DS1631 or DS1620.

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