Park-Aid Modification


Three-step beeps signal bumper-barrier distance

Circuit diagram:

GIF

Parts:

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 Diodes

IC4_____________555  Timer IC

BZ1___________Piezo sounder (incorporating 3KHz oscillator)

Device purpose:

This modification was designed on request: some people prefer an audible alert instead of looking at the LED display, making easier the parking operation.

Circuit operation:

The original Park-aid circuit was retained, but please note that the input pins of IC2B, IC2C and IC2D are reversed. LEDs D5, D6 and D7, as also resistors R12, R13 and R14 are omitted. IC2B, IC2C and IC2D outputs drive resistors R15, R16 and R17 through D8, D9 and D10 respectively, in order to change the time constant of a low frequency oscillator based on the 555 timer IC4.
This allows the Piezo sounder to start beeping at about 2 times per second when bumper-wall distance is about 20 cm., then to increase the beeps to about 3 per second when bumper-wall distance is about 10 cm. and finally to increase further the beeps frequency to more than 4 beeps per second when the distance is about 6 cm. or less.

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