Parking assist circuit

Parking Assist Circuit

This parking assist circuit is designed to help park a car close to a garage wall while reversing. LED D7 illuminates when the bumper is approximately 20 cm from the wall; D7 and D6 illuminate at approximately 10 cm; and D7, D6, and D5 illuminate at approximately 6 cm. This provides an alert when the car gets too close to the wall. All of these distances may vary depending on the infrared emitting and receiving LEDs used, and are primarily affected by the color of the reflective surface. Black surfaces will significantly reduce the device's sensitivity. Obviously, you can use this circuit for other applications such as liquid level detection, proximity devices, etc.

Parking Assist Circuit Operation

IC1 forms an oscillator that drives the infrared LED with a 0.8 ms pulse, a 120 Hz frequency, and a peak current of approximately 300 mA. D1 and D2 are placed in a straight line, facing the car, a few centimeters apart, and fixed to a short breadboard on the wall. D2 receives the infrared beam generated by D1 and reflected by the front surface. The signal is amplified by IC2A and peak detected by D4 and C4. Diode D3, along with R5 and R6, compensates for the forward diode voltage drop of D4. A DC voltage proportional to the distance between the reflecting object and D1 and D2 is fed to the inverting inputs of three voltage comparators. These comparators switch the LED based on the voltage at their non-inverting inputs (set by the voltage divider chain R7-R10).

part:

R1_____________10K 1/4W resistor

R2, R5, R6, R9 _____ 1K 1/4W resistors

R3_____________33Ω 1/4W resistor

R4, R11__________1M 1/4W resistors

R7______________4.7K 1/4W resistor

R8______________1.5K 1/4W resistor

R10, R12-R14 _____1K 1/4W resistors

C1, C4___________1µF 63V electrolytic or polyester capacitors

C2_____________47pF 63V ceramic capacitor

C3, C5_________100µF 25V electrolytic capacitors

D1_____________Infrared LED

D2_____________Infrared photodiode (see note)

D3, D4________1N4148 75V 150mA diode

D5-7___________LED (Any color and size)

IC1_____________555 Timer Integrated Circuit

IC2___________LM324 Low-power Quad Operational Amplifier

IC3____________7812 12V 1A Positive Voltage Regulator Integrated Circuit

Circuit modification:

A circuit modification with an audible alarm instead of a visual alarm can be found here: Parking Assist Modification

Note:

The power supply must be regulated (hence IC3) to obtain an accurate reference voltage. The circuit can be powered by a commercial wall adapter with a DC output voltage in the range of 12-24V.

Current consumption: 40mA when LEDs are off; 60mA @ 12V DC power supply when all LEDs are on.

The infrared photodiode D2 should be of the type with an optical sunlight filter: these components are housed in a black plastic casing. It's somewhat similar to the TO92 transistor: in this case, note that the sensitive surface is curved, not flat.

Avoid direct sunlight or artificial light exposure to D1 and D2.

If your car has a black bumper, you can align the infrared diode with the (mostly white) license plate.

A more sensible approach would be to house all the circuitry in a small box near the infrared LEDs. The three signal LEDs can be positioned at a height away from the main box, making them easily visible to the car driver.

The optimal setup is to bring D2 close to D1 (a non-reflective object) until D5 lights up; then move it slightly until D5 is noticeably off. The ideal distance between D1 and D2 is typically in the range of 1.5-3 cm.

If you need a simpler circuit to drive LEDs or relays, please click on the infrared level detector.