parking aid senses distance to rear of v

Three LEDs signal bumper-barrier distance

Infra-red operation, indoor use

Circuit diagram:

Parking aid senses distance to rear of v


R1_____________10K 1/4W Resistor

R2,R5,R6,R9_____1K 1/4W Resistors

R3_____________33R 1/4W Resistor

R4,R11__________1M 1/4W Resistors

R7______________4K7 1/4W Resistor

R8______________1K5 1/4W Resistor

R10,R12-R14_____1K 1/4W Resistors

C1,C4___________1΅F 63V Electrolytic or Polyester Capacitors

C2_____________47pF 63V Ceramic Capacitor

C3,C5_________100΅F 25V Electrolytic Capacitors

D1_____________Infra-red LED

D2_____________Infra-red Photo Diode (see Notes)

D3,D4________1N4148 75V 150mA Diodes

D5-7___________LEDs (Any color and size)

IC1_____________555 Timer IC

IC2___________LM324 Low Power Quad Op-amp

IC3____________7812 12V 1A Positive voltage regulator IC

Device purpose:

This circuit was designed as an aid in parking the car near
the garage wall when backing up. LED D7 illuminates when
bumper-wall distance is about 20 cm., D7+D6 illuminate at about
10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted
when approaching too close to the wall.

All distances mentioned before can vary, depending on
infra-red transmitting and receiving LEDs used and are mostly
affected by the color of the reflecting surface. Black surfaces
lower greatly the device`s sensitivity.

Obviously, you can use this circuit in other applications like liquids level detection, proximity devices etc.

Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of
0.8mSec. pulses at 120Hz frequency and about 300mA peak current.
D1 & D2 are placed facing the car on the same line, a couple
of centimeters apart, on a short breadboard strip fastened
to the wall. D2 picks-up the infra-red beam generated by D1 and
reflected by the surface placed in front of it. The signal is
amplified by IC2A and peak detected by D4 & C4. Diode D3,
with R5 & R6, compensate for the forward diode drop of D4. A
DC voltage proportional to the distance of the reflecting object
and D1 & D2 feeds the inverting inputs of three voltage
comparators. These comparators switch on and off the LEDs,
referring to voltages at their non-inverting inputs set by the
voltage divider resistor chain R7-R10.


Power supply must be regulated (hence the use of IC3) for
precise reference voltages. The circuit can be fed by a
commercial wall plug-in power supply, having a DC output voltage
in the range 12-24V.

Current drawing: LEDs off 40mA; all LEDs on 60mA @ 12V DC supply.

The infra-red Photo Diode D2, should be of the type
incorporating an optical sunlight filter: these components appear
in black plastic cases. Some of them resemble TO92 transistors:
in this case, please note that the sensitive surface is the
curved, not the flat one.

Avoid sun or artificial light hitting directly D1 & D2.

If your car has black bumpers, you can line-up the infra-red
diodes with the (mostly white) license or number plate.

It`s wiser to place all the circuitry near the infra-red LEDs
in a small box. The 3 signaling LEDs can be placed far from the
main box at an height making them well visible by the car driver.

The best setup is obtained bringing D2 nearer to D1 (without a
reflecting object) until D5 illuminates; then moving it a bit
until D5 is clearly off. Usually D1-D2 optimum distance lies in
the range 1.5-3 cm.

If you are needing a simpler circuit of this kind driving a LED or a relay, click Infra-red Level Detector

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