DaveEvans:
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).
So do you mean that the device must be "physicaly" hacket? As i wrote i used NewPing library for inspiration.
So i use some code from boolean NewPing::ping_trigger() for "transmitter".
And receivers input set up to listenig view digitalRead() arduino nativ method.
DaveEvans:
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; ....
But i need waterproof device. On the other hand its may be good proof of concept.