On a sunny day (Fri, 28 Feb 2020 22:38:54 +0000 (GMT)) it happened "Dave
Liquorice"  wrote in
:

>On Fri, 28 Feb 2020 22:01:34 GMT, Alister wrote:
>
>>> Presuming common CMOS thresholds of 30 and 70%: <0.99V is LOW,
>>> 2.31V is HIGH. What the circuit does between those thresholds is
>>> indeterminate (I'd hope it holds the last valid state until the
>far
>>> threshold is crossed).
>>
>> that is exactly what does NOT happen.
>> the logic sate will flip at some in-determinant point between the two
>> thresholds.
>
>And even when it has flipped it can flip back again if the signal
>remains between the thresholds. Hence the requirement for pull
>up/down resistors.

An other effect that may happen on a slow rising (or falling) edge is
oscillations, usually a minimum rise-time is specified for analog inputs.
A thermistor would not be fast as we talk about nano seconds here.
With a large capacitor at the input like an other poster showed in his solution
chances of oscillations happening ere likely zero.

Schmitt-trigger inputs will not normally oscillate but flip state and stay
there unit
the input is a lot changed the other way,
but will be an oscillator when you add a capacitor :-)



I used a i2c ADC chip from Philips PCF8591 as 4 channel analog input
and 1 channel analog output on the parport of my old PCs in the eighties.
Probably have some old C driver code for it around somewhere.
Else these days Linux should have support for it as I see it in
 /usr/src/linux/drivers/i2c/chips/pcf8591.c

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