could you help me how to make trigger pulse?

Thread Starter


Joined May 23, 2021
hello i'm cnu university student.

help me please

i will design analog circuit. i can't use a digital unit but i can use 555timer.
i will make water level detection circuit.
when the water arrives setting level, led will notice for user.
after 5 seconds, motor need to operate to close the window.
so i will use 555timer - monostable mode and i need to know how to make trigger pulse.

could you help me?


Joined Feb 24, 2006
Making a pulse is fairly easy and straightforward. Making one with particular characteristics is only slightly more challenging. You have not really given us much to go on. Can you show us a schematic of what you have so far and maybe enhance your description of the kind of pulse you are looking for.


Joined Feb 24, 2006
I'm not sure what you mean by a "digital unit". Can you elaborate, and explain why a 555, which contains a digital SR flip-flop does not qualify as a "digital unit"?


Joined Aug 7, 2008
I see that post was relocated, hope that you can find it. My yesterdays post did not make it- forgot to hit " Post reply" ?
IF 555, pin 2 is tied high with 1 to 5 meg. resistor and attached to a probe, a second grounded probe is in contact with water, now if water rises and makes contact with first probe - pin 2 will be pulled low triggering 555. (direct answer removed by moderator) You may want a reset at turn on.
Post a drawing for review.
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