I have a problem i use a ultrsonic sensor, and when i send a pulse out of 4V then a couple of ms i have a pulse back on the input, how can i exactly know how much time there is between the 2 ^pulse??
Use the output pulse to trigger a counter in period measuring mode and stop the counter on the return signal (if the input return signal is large enough to reliably trigger a logic circuit). If the signal is not large enough to trigger the counter directly, an external comparator can be used to generate the stop signal.
Another approach is to use two channels of analog input. Feed the output signal to one of them and the return signal to the other channel. The time between outgoing and return pulses can be determined from the sampling rate. If precise timing is required and your AI board does not have simultaneous sampling, you have to account for the inter-channel time as well.
