Ultrasonik sensör

[Audioguru]

Your link from Taiwan does not work (404 error) says it is not secure and is in the Chinese language.

Your receiver circuit uses a low frequency passive rectifier diode instead of a much more sensitive and faster active rectifier/peak detector circuit.

 

[FvM]

There was a problem with the link placement in the post, now fixed.

But I'm undecided on how to convert the frequency of my receiver sensor to voltage. I'm having trouble setting up the circuit on the receiver part.

Actually you are measuring sensor signal magnitude, not frequency. The detector filter time constant must be adapted to the intended response time. The circuit in post #3 has several 100 ms time constant, but you are asking for low ms response time.