Pointy:
but the 250ms is the length of a single beep, the gap between beeps can be hours or so fast that they sound like a continuous tone, as in my sample mp3 above.As it seems the smallest individual pulse width is 250ms (note as I don't have an oscilloscope to measure so I simply recorded a beep in Audacity to measure it) then sampling at 100ms should be safe, but this could easily be shortened.
OK, if the pulse width is 250msecs then sampling at 100msecs should be fine. I had assumed the "noise" you posted was the tone, not the stream of pulses.
When I was using the ISR to count a rapid stream of beeps, it appears as one long pulse so it only registered as one count. This is why I changed to the above code.
In simple terms again, I just want to count the pulses during a set period or the time the pulse is low. So in theory 1 single 1 second pulse or 10 single pulses during the timing period would be treated the same in the above code.
Sorry, Les but I'm still not making sense of this.
I thought you are using the ISR to detect the first pulse and are them sampling to detect the next 2 pulses (making 3 in all) and then waiting some time before starting over.
It's not clear to me why the ISR (on a falling edge) woudn't detect every pulse just as easily as sampling.
I don't understand how 1 in 1 second or 10 single pulses relates to counting 3 pulses.
Perhaps if you explain why you are doing this I might understand better.
...R