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How can I count the number of middle pulses from the given signal

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tranvannhancu:
Hi all,

I have the following signal where I need to design a circuit to count the number of pulses.

The pulse is at the middle. There are valleys before and after each pulse.
The amplitude of pulses are also different.

Could anyone guide me on what kind of circuit I can use to do this?
Thanks!

moffy:
Use a small micro for logic and say a comparator with a threshold of 300mv and some hysteresis or just feed the signal into the ADC of a small micro and do all the filtering, detection and counting in code.

2N3055:

--- Quote from: tranvannhancu on July 05, 2024, 10:11:54 am ---Hi all,

I have the following signal where I need to design a circuit to count the number of pulses.

The pulse is at the middle. There are valleys before and after each pulse.
The amplitude of pulses are also different.

Could anyone guide me on what kind of circuit I can use to do this?
Thanks!

--- End quote ---

On that image, number of positive pulses in the middle of that negative pulse is same as all those groups...
That whole valley before, pulse in the middle and valley behind repeats as a group.

I would detect first negative going edge, ignore everything for a time length of a group, and then be ready to detect another one..
Either AC couple the signal and use negative going zero pass detector, or if DC levels are stable a comparator (with some hysteresis) to detect edge. And then you can use microcontroler to read state, ignore changes for the short period, and count the groups..

PCB.Wiz:

--- Quote from: tranvannhancu on July 05, 2024, 10:11:54 am ---The pulse is at the middle. There are valleys before and after each pulse.
The amplitude of pulses are also different.

--- End quote ---
You have not said how that varies (aside from the middle peak) and if you need to reject any pulses.

A simple scheme would be a comparator that slices on ~50% of the negative swings, feeding a counter, and you divide by 2 / shift right 1 bit, as you increment by 2 every pulse.

Modern Rail-Rail comparators with push pull outputs, often have inbuilt hysteresis.
Your signal looks quite slow, so you could add more noise filtering by adding a RC filter between the Comp output and a counter with a schmitt trigger clock.

CaptDon:
Trigger a one shot from the negative going leading edge (probably through a comparator) and set the one shot so it can't retrigger until after the duration of your total pulse width plus about 10%. The negative side of your pulses look uniform and of the same width within a few percent. What will be your time base? You say you want to count the number of pulses?? Total number? How many occur in a second, a minute, a year? You could build a reliable circuit with a comparator with adjustable threshold and a one shot 74LS121 with variable 'non-retrigger' timeout. 74LS123 won't be suitable because it is retriggerable during the current pulse. A 555 may work as I think they have to time out before being retriggerable. In any event I could do it with two very simple readily available I.C.'s and just a very few resistors and a couple of capacitors.

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