Thermistor

Using Arduino Project Guidance
#1

Hi

I am using this Thermistor:

http://datenblaetter.physicalcomputing.at/Temperatursensor.PDF

With this code:

http://www.arduino.cc/playground/ComponentLib/Thermistor2

(Simple Code).

I am quit sure that the Temperature I get is wrong.

However the Temperture changed with where I put the resistor.

So if AnalogPin0 and the 10K resistor is near to each other I get 5 Celsius/41 Fahrenheit.

If I put a little breadboard cable in between them I get 334 Fahrenheit.

Both of these values are unlikely.

I am in room with about 15-20 C

Somewhere I read that changing the resistor to a smaller resistance (from 10K to 1K).

Also stating that the temperature range I want to measure should be adapted to the resistor.

I want to measure 0-50 Celsius. And if outside -50-50 Celsius (Just to be sure)

Is that true?

Thanks for the time.

#2

The data sheet is for a range of thermistors, which one have you got ?. The resistor you use with it and the code you use will vary depending on the properties of thermistor. If it isn't absolutely correct the reading can be miles away from reality. I gave up to thermistors and went to Maxim DS1820 digital thermometers.......

#3

Cool. Thanks for that link. Does this 1 wire digital thermosensor work with arduino? Do you have a simple working code example for this sensor?

Thanks again! :)

#4

I am quit sure that the Temperature I get is wrong.

However the Temperture changed with where I put the resistor.

So if AnalogPin0 and the 10K resistor is near to each other I get 5 Celsius/41 Fahrenheit.

If I put a little breadboard cable in between them I get 334 Fahrenheit.

Both of these values are unlikely.

Need to know you've wired things up to help...

#5

Does this 1 wire digital thermosensor work with arduino? Do you have a simple working code example for this sensor?

http://www.arduino.cc/playground/Learning/OneWire

I have 5 of them on the same arduino digital pin on my monitoring system.

A bit pricier than thermistors but they are accurate and don't need graduating.

http://pluggy.is-a-geek.com/

#6

I use the Dallas chips as well.

If you are going to collect Air Pressure as well -- look at the BMP085 chip. It has temp and pressure.

#7

Attached a image of my setup.

Black goes to 5V
Blue goes to GND
Yellow to Anlog Pin 0

Dallas 1-wire seems nice, but I would like to get something going soon.

Any suggestions why my setup does not work?

temp.jpg

#8

"The data sheet is for a range of thermistors, which one have you got ?. "

Did you answer that question? Did I miss it?

Also -- I don't see your code posted here. There are two example and I have no idea if you know how to copy the code correctly. [u]Please don't waste time claiming this is an insult.[/u] I have copied code incorrectly myself.

And you said: If I put a [u]little[/u] breadboard cable in between them I get 334 Fahrenheit.

You do NOT get a temperature reading! The calculated temperature is presentation. The voltage reading is reality. The Arduino reading is an interpretation as well.

One other question. Why is the word little there? Do long cables behave differently in these circumstances? If not do not use any unnecessary words -- because we then have to determine if the words do indeed have significance. Maybe [u]your[/u] long cables have resistors in them and you expect us to know that. Again this is not a nit-picking point. If you don't believe me plow through other posts and see this point raised....

[u]You get a voltage reading -- which the Arduino presents as a number -- which you interpret using math.[/u] This is not nit-picking -- it's reality.

As someone said in another thread-- a glass of water with ice gives you 0 deg. C or 32F deg. -- then you can calibrate your readings as you see fit.

Since you did not tell us [u]exactly[/u] which thermistor I have no idea what the math should be. I know I should be able to read the color codes, but I have bins of color coded components and thank goodness I have an ohmmeter as some companies have orangey-reds they use to mark the components.

Color Coding:

Use RED to voltages and Green or Black to ground. There are some conventions. and many variations tis true....

#9

Dear Georgina

Thank u 4 ur response (short enough :-).

You are hilarious. And I dont mean that in a bad way.

Well so let me answer your question:

  1. I bought this sensor kit:

http://www.physicalcomputing.at/shop/article_A-1107500/Sensor-Kit-Basic.html?shop_param=cid%3D5%26aid%3DA-1107500%26

In there is this sensor:

http://www.physicalcomputing.at/shop/article_A-1101400/Temperatursensor.html?shop_param=cid%3D5%26aid%3DA-1101400%26back%3Dparent%26

If you click on Datenbatt (Datasheet in German) you get the pdf I posted here.
I would be happy to know myself which one is mine.

Do Thermistor have the same colorcode as regular resistors?
If so from top to bottom (gold-orange-red)

I thought the whole concept is that the resistance changes with temperature.

  1. Code: As mentioned above. Simple Code from the page I indicated. But here it is.
    I commented out Celsius to Fahrenheit:
#include <math.h>

double Thermister(int RawADC) {
 double Temp;
 Temp = log(((10240000/RawADC) - 10000));
 Temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * Temp * Temp ))* Temp );
 Temp = Temp - 273.15;            // Convert Kelvin to Celcius
// Temp = (Temp * 9.0)/ 5.0 + 32.0; // Convert Celcius to Fahrenheit
 return Temp;
}

void setup() {
 Serial.begin(9600);
}

void loop() {
 Serial.println(int(Thermister(analogRead(0))));  // display Celsius
 delay(1000);
}
  1. “Do long cables behave differently in these circumstances?”

Dont know. You tell me.

  1. “As someone said in another thread-- a glass of water with ice gives you 0 deg. C or 32F deg. – then you can calibrate your readings as you see fit.”

How does the calibration work. After I stick the sensor in a glass of icewater it gets “reset” to zero and then works.
Or is this to know what I am measuring. I am sure that my room did not have 5 degrees.

Thanks a little :slight_smile:

#10