[SOLVED] Pulse interference

[EngineerJulian]

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?

 

[KlausST]

hi,

please provide a sketch.

Klaus

 

[EngineerJulian]

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

 

[barry]

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.

 

[EngineerJulian]

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.

 

[FvM]

A comparator with 6V threshold? Possibly combined with a low pass in front?

 

[barry]

The 12v pulses are an output signal. The tiny pulses are coming from an 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.

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?

 

[KlausST]

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

 

[barry]

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

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.

 

[KlausST]

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.