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Temperature sensor with cool thermistor Answered

Hi, I am trying to make a temperature sensor using a thermistor. I've made a basic circuit using an Arduino and some tutorials from this site and couple others, which works well but the thermistor heats up way too much - perhaps to about 50 or 60 degrees - but it needs to stay around room temperature for my application. I'm using a 5V output from an Arduino through a 15Ohm thermistor - am I doing something wrong?
Many thanks for the help!

The one I've made is almost identical to the one in this tutorial: http://www.circuitbasics.com/arduino-thermistor-temperature-sensor-tutorial/ except a different thermistor

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Downunder35m

1 year ago

Sorry but I can't follow...
You say you use a thermistor to measure temp but state your thermistor is heating.
Either you are doing something wrong or I missed the point here.

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Mickey_blu_eyesDownunder35m

Reply 1 year ago

Yea, I have the thermistor and the resistor of same resistance connected in series to the 5v output of the Arduino. By determining the changing resistance of the thermistor and relating this to its temperature, it gives a readout of the temperature of the thermistor. But putting the 5V through the thermistor already causes it to heat up significantly - apparently you can correct for this, but I can't have the thermistor that hot for what I need it for. As you've probably guessed I'm not very good at electronics - I'm asking how to keep the same setup, but minimise the self-heating of the thermistor. It's only 15Ohm - would making it a higher resistance make it heat up more or less? I assume more. What about making it bigger or smaller for example? Would putting a lower voltage or lower current through it make it heat less and then if so how would you implement that with the setup I have already? Thanks for your help downunder

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caitlinsdadMickey_blu_eyes

Reply 1 year ago

So....

Are you sure you are using a thermistor component? Is it wired the same way as the tutorial you link to? 3 wires for the setup and arduino analog pin connected to where the thermistor and resistor join?

I don't think thermistors self-heat but should be acclimating itself to the external air around it or the object that you glue it on/make contact with. It should just be a temperature probe. Is there a datasheet to tell exactly what resistor you should pair it up with? Maybe post the code you are using or describe better what application you are trying to use a thermistor for. And 50 or 60 degrees F or C? 15 Ohm or 150 Ohm resistor?

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Mickey_blu_eyescaitlinsdad

Reply 1 year ago

Yes its a thermistor and whole thing exactly same (wiring, connections and code) as tutorial in link (except using 15 Ohm thermistor and resistor, rather than 15k Ohm as in tutorial). 50 or 60 degrees Celsius as well. I will try a higher resistor and see if that helps cheers

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Downunder35mMickey_blu_eyes

Reply 1 year ago

There is your problem...
15 Ohm is far too low for anything good with Arduino and no wonder it all heats up.
You are pulling close to 170mA, which is too much for the Arduino anyway.
And set up like this you will never get any temperature readings, just a tiny heater that actually should not even get warm....

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Downunder35mMickey_blu_eyes

Reply 1 year ago

1. I would use a much higher resistor instead of the one you currently use - the change for the thermistor relates to temp, having too much current going through is what causes the heatup.
In an ideal case the current going through the thermistor is not really worth to mention and won't cause any problems.

2. If you are after temp readings this way IMHO it would be easier to "borrow" some code from the Marlin 3d printer software.
Here all temps are controlled by PID control and rely on very accurate and fast temp readings.
This is done through tables for the most common types of thermistors.
By utilising this code and the tables for your type of thermistor you will get very accurate readings without and overheating problems of the thermistor itself.
All thr ground work you still need to do to get more or less accurate readings was already done for you ;)

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Mickey_blu_eyesDownunder35m

Reply 1 year ago

Hi Downunder, thanks for the advice. I will try a higher resistor and see if that helps. How do I get the Marlin code btw?