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using thermistor to cause an interrupt.

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electricity86

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I would like to implement a thermistor on my PCB, So when it gets too warm, and the its resistrance decreases, then somehow it will cause an interrupt to the MCU, so i'll know about this warming.
Do you have any idea which will be low cost and very few components to design it?

Thank you.
 
There are 2 types of thermistor, NTC and PTC. The one you're saying is the NTC (negative temperature coefficient). This is normally used in temperature sensing. It decreases the resistance as the temperature rises, thus, negative. The temperature response of this device is logarithmic and that is why it is more stable in temperature sensing. On the other hand, the PTC has the reverse effect as far as temperature is concern. It increases its resistance as the temperature rises. But the temperature response has a significant difference with the NTC. The resistance only rises suddenly at the temperature threshold. Meaning, if it is rate at 85ºC, the resistance is low before 85 and increase to its max resistance as it reaches 85. The application for PTC is usually for resetable fuse.

So, it depends on your requirement. Choose which one you want and I will help in the design (of course, thru this forum. So that others can have an idea also).
 
right, you can read voltage instead of resistor in a properly set circuit. don't forget to amplify the signal before putting it into ADC, so that u will have a better resolution.
 
In this case, you may use this simulation tool from murata.

[muRata]MMCSV Download Service

Of course, we should be reading the equivalent voltage and input it to an ADC. Most microcontrollers have programmable resolution, so its up to you.

You can also use the built-in, but I would not suggest this. Much error is introduced. The error is mainly affected by the self-heating of the device.
 
You could us an external comparator to generate a signal and feed it to your uC's external interrupt pin.

But why an interupt? Use the uC's onboard ADC to read the sensor as part of the progam.


What is a uC's?
I'd rather have a circuit with low cost componetns, preferably resistors, diodes or transistors (something which is available).

And what sensor are you talking about?

p.s. i'm not writing from the account there is in where i work, so sorry for the double name.
 
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right, you can read voltage instead of resistor in a properly set circuit. don't forget to amplify the signal before putting it into ADC, so that u will have a better resolution.

Read the voltage of what?
I dont need the themistor to know if the PCB gets warmed?
 
In this case, you may use this simulation tool from murata.

[muRata]MMCSV Download Service

Of course, we should be reading the equivalent voltage and input it to an ADC. Most microcontrollers have programmable resolution, so its up to you.

You can also use the built-in, but I would not suggest this. Much error is introduced. The error is mainly affected by the self-heating of the device.

Thank you.
I just came back and i'll reveiw it when i'm organized it and will update here my comments on it (hopefully it will be usable for me :)).

About your comments, i dont understand, the ADC needs to read what voltage?
"You can also use the built-in", what built-in?
I really dont understand.
 
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To Chaerl:

"The resistance only rises suddenly at the temperature threshold. Meaning, if it is rate at 85ºC, the resistance is low before 85 and increase to its max resistance as it reaches 85ºC"


A PTC thermistor simply increase in resistance as the temperature rises.
Only special thermistors have the characteristics you mention.
 
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Ideally (maybe straight from college books), PTC should work this way. The resistance should rise as the temperature rise. But, as the manufacturers said, it's quite difficult to dope the PTC in order to have in this manner. Normally, PTC are switching type.

I have ask murata before if they have a PTC that is linear with respect to temperature. They explained to me more on the chemistry side in which I don't understand a thing. In short, it's difficult for them to produced such PTC. I don't know with other suppliers.

Some notes also from wikipedia where the writer says that most PTC's are switching.

Thermistor - Wikipedia, the free encyclopedia

They explain here more about in chemistry rather than electronics. :)
 
What is a uC's?
uC is a microcontroller
I'd rather have a circuit with low cost componetns, preferably resistors, diodes or transistors (something which is available).

The net should have several examples or reading a thermistor using an ADC (Analog to Digital Converter).
Most uCs have them built it.


And what sensor are you talking about?
the thermistor
p.s. i'm not writing from the account there is in where i work, so sorry for the double name.

See bold withing quoted text.

First you say
I would like to implement a thermistor on my PCB, So when it gets too warm, and the its resistrance decreases, then somehow it will cause an interrupt to the MCU, so i'll know about this warming.

Then you say
I dont need the thermistor to know if the PCB gets warmed?

Rather confusing :confused:, you used a few too many its.
Are you saying you want the thermistor isolated from the PCB and measuring a different temperature ? That does not change the circuit.
 
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