ultrasound thermin without µC

Hello
It's possible to do a project like this but without µC ?
https://www.youtube.com/watch?v=_g-c0N42u-A

I Only need to generate sound (100Hz to 1000Hz) function of obstacle distance, more lower is the distance to the obstacle more higher is the frequency of sound.

Here is a synoptic schematic of circuit without µC.
The Tx sent ultrasound wave every 1 second if no echoes, but, in presence of obstacle, Rx signal are amplified, and transmitter send immediatly an other ultrasound wave.

At 300m/s (30cm/ms) the tx sent the second wave after 8ms, ( 120 X 2 / 30 =8ms), the spaker sent an audio sound at (1/8) X 1000 = 125Hz

At the lower distance (approx 15cm) this frequency is 1000Hz

what do you think about this idea, and what's the best electronic circuit to do this ?

The principle seems fine. The receiver will need to have high gain if you intend to detect obstacles at a distance > a few cm, will require filtering to discriminate against sounds other than your transmitted ultrasonic frequency, and may need AGC to handle a range of distances.