What is the best way to design a transmitter and receiver circuit for an ultrasonic sensor ? I have previously designed the TX using MAX232 so that I can give a 20V p-p input to the ultrasonic speaker. For the RX circuit I used a simple amplifier(3 stages) to receive the signal. The issue is the circuit is very unstable and it is not giving consistent outputs, and the sensed distance is very small.
1.What improvements can I make to increase the sensed distance ?
2. How to stabilise the output for repeatability ?

 

Welcome to AAC!
We need more details to provide meaningful help. Do you have a link to the ultrasonic transducer's specification? Can you post a schematic of your Tx and Rx circuits, with component identifiers and component value?

 

The sensors and transmitters - if cheap end, the ZP-3 capsule from russia made beepers produced at Ukraine (about 1 W max)- exists a two feet and three feet versions. If more powerful, piezo emitters from Aliexpress (over even the kW). Cheap but powerful also are piezo cigarett lighter rods.
The boost of sensitivity: apply the synchrone detection aka PLL. One brilliant PLL tablet is 568 IC, produced for TV IR switching. The best expected result is 70-140 dB of increase. Only the drawback is need for phase clocking - somehow must transmitt the clk signal otherhow effect is diminished down to region of 60-80 dB. Other likely not so modern method is russian 140YD13 (PLL with 0.5 microvolt opamp) with good opamp afterwards, giving the sensitivity at least into microvolt scale. Sorry the any nowadays popular self-nullifying microvolt opamps are undisputable too slow. However, taking in account the "microphone" here is MOhm scale unit, You need a femtoampere scale rather not a microvolt scale, and then the keywords may stand LMP7721 (very caprice), MCP6271, MCP601, MAX44242, LMC6482-6484, ADA4530, LMC6041 and several more. Yet I dont give any coin if brute force amplification without PLL will be ineffective. PLL synchro signal may transmit, for example, by radio, or provide by digged in earth the cable.

 

The best way to design a transmitter and receiver circuit for an ultrasonic sensor is to understand both the application and the characteristics of the particular devices,both impedance and voltages. Knowing the required transmitter power, and the frequency, are needed to design the transmitter circuit. For the receiver circuit, knowing the amplitude of the anticipated signal, and the frequency, as well as the required amplitude of the receiver output signal are needed. Without that information, one random guess is as good as any other guess.