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Park-Aid Modification

Three-step beeps signal bumper-barrier distance
Infra-red operation, indoor use

Circuit diagram:

Park-Aid Modification



3K3 1/4W Resistor


330K   1/4W Resistor


470K   1/4W Resistor


150K   1/4W Resistor



1µF 63V Electrolytic or Polyester Capacitor



1N4148 75V 150mA Diodes



555 Timer IC



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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