Ultrasonic range sensor

I bought 10 on these...
https://www.goldmine-elec-products.com/prodinfo.asp?number=G14050&variation=&aitem=2&mitem=6
Ultrasonic receiver/transducer units. I am planning on using them on a bot to make it autonomous and sense when it is too close to a wall. Do I have to use two of them, one to send the pulse and one to receive or can I send a pulse out, then start timing till it receives its own pulse?
Thanks!
~Mike

Either way will work, but using two would be a simpler design. If you use one, the receiver has to be protected against the transmitted pulse.

You would also need to buy a transducer intended to be used that way, most are matched pairs - the transmitter is series resonant, and the receiver parallel resonant - neither works well for the others job.