Counter - Start counting on external low to high transition

Hi
I am trying to use an arduino to control a generator with a mechanical governator by means of a servo.

I want to set a timer in such a way that it only starts counting after a high to low transition, given by an external synchronization device. Is there any library I could use for such purpose or is it easy enough to access one of the hardware timers?

You can access the hardware timers via the millis() and micros() functions. Starting a "counter" makes no sense, unless the "counting" happens at regular intervals, which millis() and micros() already handle.

amvcs08:
I want to set a timer in such a way that it only starts counting after a high to low transition, given by an external synchronization device. Is there any library I could use for such purpose or is it easy enough to access one of the hardware timers?

I think it would help if you describe how you think your program should work. If you already have some code please post it (using code tags, please). If not, just write a list of the steps that the program will need to take.

What is the purpose of counting? Is it to measure RPM?
What is the "external synchronization device"?

...R

Notwithstanding the previous comments on what you want to do, the trigger on low to high is what this example does. The pullDOWN resistor keeps the pin low until the switch takes it high: that's what your as-yet-anonymous device will do. You'll need to check its voltage is safe for Arduino, else have some kind of level changer like maybe a divider or an opto-isolator.