[SOLVED] Pulse interference

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EngineerJulian

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Hello

I have an output signal that supposed to send 12v pulses out for RPM measurement, but the signal is picking up a smaller pulse before each 12v pulse which seems to be noise coming from another source. Is there a way to filter out smaller voltages and keep the intended 12v pulses?
 

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The smaller pulses are circled. I need to keep the bigger square pulses.
 

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First of all, it’s not clear that those little glitches are even a problem. There’s no way to tell WITHOUT A SCHEMATIC or any other useful information.
 

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The 12v pulses are an output signal. The tiny pulses are coming from a another high powered electrical spark. When the high power spark is removed, the tiny pulses disappear and the output signal is read correctly. So what I am looking for is something to attach the end of the output signal that could filter out these pulses.
 

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Again, why do you think those glitches are a problem? They only go slightly positive; what is the signal driving? or, are you concerned about the negative part of the glitch damaging some downstream IC?
 

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Hi,

I guess no - even mediocre designed - circuit will have trouble with this signal.
There must be something really badly designed.
We can´t see ... because you don´t show..

I can´t see how the negative going impulse could create a problem. If needed it could be camped by a simple diode.
And the positive pulse is so tiny it should cause no trouble.

Klaus
 

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The only concern I would have with the negative pulse is that ICs can have an absolute minimum input voltage of 0.3 or so volts below ground. A silicon diode is not going to help here. Current limiting might, but we don't have enough(any) information.
 
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I absolutely agree.
One needs to read the datasheet to decide on the right protection circuit.

Often when there is a very low negative voltage specified (like -0.3V)... it is just to avoid the internal diode becomes conductive. (same for the positive side)
In this case, there is often a note that this limit may be exceeded...IF...the current is limited to a certain level.

Klaus

Btw: I did not focus on protection, as I assume the OP is more concerend about false RPM readings.
 

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