You are proposing to use that distance sensor in a completely non-standard way. Good luck with that.
But i dont know if is there any synchronization during triger and echod signal .Do you know any other possibility?
i want to use this sensors for sending and receiveing some frequency signal based on FSK.
Seems like a sort of OOK might work...a. IF the device can be hacked to make a transmitter that can send the normal 8 pulses at any time (and not wait for an echo), and b. IF it can be hacked to make a receiver (by the method mentioned in the 3rd para above in post #4).
Another way to make a remote receiver would be to poll the output of one of the amplifying op amps downstream of the receiving transducer. That can be done with the HC-SR04; ....
Second sensor be some-how (for now i dont know how) in water...
But i need waterproof device.
What do you mean by "in water"? Do you mean: (1) below water, as in "underwater" or (2) in water, as "in a boat and might get splashed or occasionally wet"?
Does this sensor work (in the normal way, as a distance sensor) underwater?