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Topic: HC-SR501 pir detector pot failure (Read 57 times) previous topic - next topic

guy_c

Mar 11, 2019, 12:53 pm Last Edit: Mar 11, 2019, 07:53 pm by guy_c
Hello everybody,

I am noticing on few of these modules that after few years age the pulse width adjustment potentiometer has one of it's pin disconnected from the inner resistive track, in the last case, it was the pin which connects to 3 of the biss0001.

How do I realize that? this pulse width pot is set to 0 giving~2.5". As part of the debouncing procedure my code checks that the pulse is not tooLongHi, in my case 5", because this could indicate that there is an open, e.g due to snatched cable/sensor etc. Since the sensor connects to an INPUT_PULLUP, this result in input being high longer than the set pulse width.

I believe that the sensitivity pot -which I usually set to mid range ~ .5 Mohm- is not better and so the fix I adopted is to short the pulse width pot and replace the sensitivity one by a resistor.

atached pics




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