cant design a thermistor as an interrupt source

rainman1

New Member
I need a design a circuit that includes NTC as an interrupt source for MCU.
When it gets warm, the MCU pin needs to receive 3.3V.
I have to power sources for the circuit, and can use one of them - 3.3v and 5v.
the MCU pin can only sink up to 4mA.

Any ideas?

Thanks!

More:
I havent picked a right NTC yet, i'd like it to be around 10Kohm, but its not a must.
 
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I though of something like that:


Where R1 is the NTC.

Edit:
What is your opnion?

To Blue.
I'd like to use resistors only, i needed to mention it in topic.
 

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Yes - what's "warm"? What's the NTC curve look like? Without a comparator you are goofing around with poorly defined trip points over what may be a uselessly small range for that digital input port.
 
Blue.
Why is it a trouble for the MCU to receive analog input within its range limit?

duffy.
The NTC is NCP15XH103F03RC, its B is little above 3000. R0 is 10Kohm
 
Current's not the problem, it's the undefined trip point voltage between Vhi and Vlow.
 
Never heard of that one. Can you point to a link, or tell me how to find it? There's 57,600 results for "analog" on the site, none of the combinations I tried showed me the link.

I've used analog signals on digital pins many times for the quick and dirty A/D trick where you time an RC circuit. Never heard of an issue with the current.
 
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In the undined region an input transistor acts analog which draws too much current. At least that is what I recall.

Could you please explain what you said?
I didnt quite understand it.
What transistor are you talking about?

*PLUS:
Why does it sink too much current over its limit?
I'm defining the input pin of MCU as tristate, so whats the problem?
(and even if i defined it as pull-up/down, still why would it draw more current?)
 
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