Parking assist system modification

Circuit diagram:

Components:
R15_____________3K3 1/4W Resistor
R16___________330K 1/4W Resistor
R17___________470K 1/4W Resistor
R18___________150K 1/4W Resistor
C6______________1µF 63V Electrolytic or Polyester Capacitor
D8,D9,D10____1N4148 75V 150mA Diode
IC4_____________555 Timer IC
BZ1___________ Piezoelectric Generator (Built-in 3KHz Oscillator)

Equipment application:

This modification was designed based on requests: some people prefer audible alarms to visual LED displays, making parking operations easier.

Circuit operation:

The original Park-aid circuitry is retained, but note that the input pins of IC2B, IC2C, and IC2D are inverted. LEDs D5, D6, and D7, as well as resistors R12, R13, and R14, are omitted. The outputs of IC2B, IC2C, and IC2D drive resistors R15, R16, and R17 via D8, D9, and D10, respectively, to alter the time constant of the low-frequency oscillator based on the 555 timer IC4.

This allows the piezoelectric generator to start beeping at a frequency of about 2 times per second when the bumper is about 20 centimeters away from the wall, then increase to about 3 times per second when the distance is about 10 centimeters, and finally further increase the beeping frequency to more than 4 times per second when the distance is about 6 centimeters or less.