how to know about the led stop blinking

[Ben]

"

--- I'm going insane, aren't I??    ---

"

... and I am in lock-step with you on the way.

Ben

[harjeemann]

dear all

i am using a square wave with a duty cycle of 50 % may be this helps u to explain problem

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[Ben]

I think our discusion of Nyquist indicates that using a camera with a 30 Hz refresh rate, the best you can do reliably is about 3 Hz flash of the LED.

You may be able to push it as far as 15 Hz but above that rate, all bets are off.

Ben

[Britoa]

I agree with everyone above, you should just use a timestamp, it is simpler. To use the LED, you will want to use NI Vision (if you already didn't know that) because you will need to have a region of interest where the LED is and then from there you can determine if it is on or off (I have never used vision, so I don't know how difficult that may be)

If you do use the LED, you will want to start blinking it at a low frequency, and slowly ramp up the speed it blinks until it stops changing between frames. at that point, you have gotten to exactly half the framerate. If the speed it blinks speeds up again as you increase after it slows down, you went too far (it will reach a similar no-change point at fLED = fcamera*n/2). I suggest you take a look at some information on sampling theory, as that's what
this is all about.

[harjeemann]

i am able to solve the problem, thank to all of you

i dont use led this time and use the property of my frame grabber

i am using matrix vision grabber so i am usingthe get object and object get frame functions of that

cheers