Sensors - Tranducers Circuits

Reverse Parking Sensor Circuit

For novice drivers, gauging distance while parking a car can be a challenging task. To address this issue, the reverse parking sensor circuit employs three LEDs to provide distance indications. This system can be conveniently installed at the rear of the vehicle and operates on a rechargeable 12V battery. In this guide, we will demonstrate how to construct a reverse parking sensor, and this same methodology can be applied to create an IR Water Level Detector Circuit.

The group of LEDs effectively communicates the car’s proximity to an obstruction, with D5, D6, and D7 serving distinct roles. D7 illuminates when the distance between the car and the obstacle is 25cm. At a distance of 20cm, both D7 and D6 LEDs illuminate, while all LEDs (D5, D6, D7) light up when the distance narrows to 5cm. If the distance exceeds 25cm, all LEDs will switch off.


  • Reverse Parking Sensor Circuit Principle:
  • Reverse Parking Sensor Circuit Diagram:
    • Reverse Parking Sensor Circuit Design:
    • How to Operate this Reverse Parking Sensor Circuit?
    • Reverse Parking Sensor Circuit Applications:
      • Limitations of this Circuit:

Reverse Parking Sensor Circuit Principle:

The parking sensor circuit can be divided into two main segments: one for the transmitter and the other for the receiver. In the transmitter section, an NE555 timer IC operates as an astable multivibrator to drive the IR transmitter, with the transmitter frequency set at 120Hz.

When an obstacle is present, the IR pulses emitted by the IR transmitter bounce off the obstruction and are subsequently captured by the IR receiver. Subsequently, the receiving signal is amplified by U2:A.

The output voltage from the peak detector, consisting of components R4 and C4, is directly proportional to the distance separating the car’s bumper from the obstacle. This voltage output is then directed into the inputs of three comparators: U2:B, U2:C, and U2:D. These comparators, influenced by the input and reference voltages, govern the status of the LEDs by toggling them on and off.

Reverse Parking Sensor Circuit Diagram:

Reverse Parking Sensor

Circuit Components:


  • NE555 timer
  • IR transmitter
  • Electrolytic capacitor – 1uF, 16V
  • Resistors – 10k, 1k, 330 ohm


  • LM324 IC (low power quad op-amp)
  • IR receiver
  • 1n4148 diodes – 2
  • Electrolytic capacitors – 100u (2), 10u, 47p, 1u
  • LED’s – 3 (5mm)
  • 1k resistors – 7
  • 1M ohm resistors – 2
  • 4.7k , 1.5k resistors
  • 12V DC battery
  • Connecting wires

Reverse Parking Sensor Circuit Design:

In the transmitter section, a 555 timer is harnessed to produce a signal operating at a precise 120 Hz frequency. To ensure stability and prevent unintended resets, the fourth pin of the 555 timer is linked to the power supply. The third pin of the 555 timer is responsible for generating the output pulse. The specific output frequency of the 555 timer is dictated by the values of resistors R1, R2, and capacitor C1.

In parallel, operational amplifier U2:A plays a crucial role by amplifying the signals received from the IR receiver. To accurately identify the peak of the amplified signal, resistor R4 and capacitor C4 collaborate to establish a peak detector circuit.

Op – amp as Comparator:

An operational amplifier (op-amp) is equipped with a single output and two inputs: one non-inverting and the other inverting. When the voltage at the non-inverting input surpasses that at the inverting input, the operational amplifier’s output registers a high voltage level.

Conversely, when the voltage at the inverting input surpasses that at the non-inverting input, the output voltage drops to a low level.

In the described circuit, the voltages applied to the non-inverting pins of the comparators act as reference voltages, and these reference voltages are compared to the inverting input voltages of the comparators to generate the output signal.

To establish distinct reference voltages at their non-inverting pins, resistors R8 through R11 come into play.

Furthermore, resistors R12, R13, and R14 are incorporated to safeguard the LEDs from potential high voltage exposure.

How to Operate this Reverse Parking Sensor Circuit?

  1. Connect the wires as shown in the circuit diagram.
  2. When an obstruction is present, arrange the transmitter and receiver so that the IR receiver receives the IR rays.
  3. When you turn on the power and move the obstacle beyond 25cm, you’ll notice that no LEDs will light up.
  4. Reduce the obstacle distance to 25 cm, and the D7 led should now shine.
  5. Reduce the distance to less than 20 cm, and both D7 and D6 leds will light up.
  6. Even if the distance is reduced to 5 cm, all LEDs will turn on.

Reverse Parking Sensor Circuit Applications:

  • This circuit can be used in auto mobiles to park the vehicle safely.
  • We can use this circuit to measure the distance.
  • We can also use this circuit as IR Liquid Level Detector by making few modifications.

Limitations of this Circuit:

  • IR receiver may receive the normal light. As a result, parking sensor may not work properly.
  • We should arrange IR sensors accurately; otherwise they may not detect the obstacle.

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