Reads a pulse (either
LOW) on a pin. For example, if
pulseIn() waits for the pin to go from
HIGH, starts timing, then waits for the pin to go
LOW and stops timing. Returns the length of the pulse in microseconds or gives up and returns 0 if no complete pulse was received within the timeout.
The timing of this function has been determined empirically and will probably show errors in longer pulses. Works on pulses from 10 microseconds to 3 minutes in length.
pulseIn(pin, value, timeout)
pin: the number of the pin on which you want to read the pulse. (int)
timeout (optional): the number of microseconds to wait for the pulse to start; default is one second (unsigned long)
the length of the pulse (in microseconds) or 0 if no pulse started before the timeout (unsigned long)