Single Element Ultrasonic transducer RX/TX switching

[carp3]

Hi,
I'm trying to use a single ultrasonic transceiver , but i have some problems with switching from RX to TX. i tried to do this with 74HC125 but i didn't get any response(echo) from transceiver . i think it's not fast enough for switching from High enabled to High impedance mode. but i don't know any other method to switch between RX and TX. my transmitter frequency is about 485khz and other parts of circuit is ok. i tested my circuit with separate transmitter/receiver and it worked. any suggestion for switching between RX and TX ?


my switch circuit:



results for separate transmitter/receiver




thanks.
(sorry for bad English )

 

[FvM]

It's not clear where you have tx and rx signal in the "separated" waveform. What's the echo TOF?

To allow understanding of possible problems of the single transducer circuit, you should show the Tx, enable and Rx waveforms. It's also not clear how your Rx amplifier manages to recover from previous Tx pulse, DC level shift during enable and how it's biased at all. Generally, single transducer operation can work, but these points have to be well considered.

A "not so good" point is the change in matching impedance from short during Tx to open during Rx. It involves a change in transducer resonance frequency. Keeping a constant transducer load impedance is probably better, although it reduces the Rx level at first sight.

 

[carp3]

i'll take some pictures from oscilloscope tomorrow. i do not disconnect/shutdown amplifier when transceiver is in TX mode. should i ?
i'll put my amplifier schematic too( tomorrow )