How to Build an ESP32 Ultrasonic Parking Sensor

Distance sensing, traffic-light LEDs, OLED readout, and beeps that speed up as you get close

ESP32 Vehicles Beginner40 minutes6 components

Updated May 27, 2026

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How to Build an ESP32 Ultrasonic Parking Sensor — For illustrative purposes only

On this page

What you'll build
Wiring diagram
Components needed
Assembly
Pin assignments
Code

What you'll build

This guide walks you through a tabletop parking sensor that measures distance with an HC-SR04P ultrasonic module, shows the live reading on a small SSD1306 OLED, and gives an obvious warning using green, yellow, and red LEDs. When an object is far away, the green LED stays on. As it moves closer, the yellow LED takes over. Inside the stop zone, the red LED lights and the buzzer beeps faster so the warning is useful without staring at the screen.

The build is deliberately bench-safe. It does not connect to a real vehicle, control brakes, or make safety decisions for you. The HC-SR04P version works at 3.3V logic, so it is a better fit for an ESP32 than the older 5V-only HC-SR04 modules. The firmware sends a short trigger pulse, measures the echo time, converts it to centimetres, smooths the reading, and updates the LEDs, display, and buzzer from the same distance thresholds.

By the end you will have a compact distance-warning box you can test with a cardboard wall, robot chassis, or desk edge. It is a good first project for learning timing, digital outputs, simple state thresholds, and sensor noise handling before moving on to a rover or any build where distance sensing affects motion.

Wiring diagram

React Flow

Components needed

Component	Type	Qty	Buy
HC-SR04P Ultrasonic Distance Sensor	sensor	1	€1.85
0.96 inch SSD1306 OLED Display	display	1	€4.30
Green LED	actuator	1	€1.60
Yellow LED	actuator	1
Red LED	actuator	1	€1.60
Passive Piezo Buzzer	actuator	1	€4.75

Prices and availability are indicative and may have been updated by the supplier. Schematik may earn a commission from purchases made through affiliate links.

Assembly

Wire the distance sensor

Connect the HC-SR04P VCC and GND to the ESP32 3V3 and GND rails, then connect TRIG to GPIO27 and ECHO to GPIO26.

Tips

Use the HC-SR04P 3.3V-compatible module, not a 5V-only HC-SR04, unless you add proper level shifting.

Warning

Do not connect a 5V echo signal directly to an ESP32 GPIO.

Add the display

Connect the SSD1306 OLED to the same 3V3 and GND rails, with SDA on GPIO21 and SCL on GPIO22.

Tips

If the OLED stays blank, check whether your module uses address 0x3C or 0x3D.

Add the warning outputs

Connect the green LED to GPIO14, yellow LED to GPIO12, red LED to GPIO13, and the passive buzzer signal pin to GPIO25. Each LED should use a current-limiting resistor.

Tips

Place the LEDs left to right as green, yellow, red so the warning pattern reads naturally.

Warning

Do not drive bare LEDs directly from GPIO without resistors.

Upload and test against a wall

Upload the sketch, aim the sensor at a flat surface, and move it from about one metre away to the stop zone. The OLED, LEDs, and buzzer should change together.

Tips

Cardboard, foam board, or a book makes a better test target than a thin chair leg.

Warning

This is a learning aid, not a safety-rated vehicle parking system.

Pin assignments

Pin	Connection	Type
3V3	hc-sr04p-ultrasonic-sensor_0 VCC	POWER
GND	hc-sr04p-ultrasonic-sensor_0 GND	GROUND
GPIO 27	hc-sr04p-ultrasonic-sensor_0 TRIG	DIGITAL
GPIO 26	hc-sr04p-ultrasonic-sensor_0 ECHO	DIGITAL
3V3	ssd1306-oled_0 VCC	POWER
GND	ssd1306-oled_0 GND	GROUND
GPIO 21	ssd1306-oled_0 SDA	I2C
GPIO 22	ssd1306-oled_0 SCL	I2C
GPIO 14	green-led_0 ANODE	DIGITAL
GND	green-led_0 CATHODE	GROUND
GPIO 12	yellow-led_0 ANODE	DIGITAL
GND	yellow-led_0 CATHODE	GROUND
GPIO 13	red-led_0 ANODE	DIGITAL
GND	red-led_0 CATHODE	GROUND
GPIO 25	passive-buzzer_0 SIG	DIGITAL
GND	passive-buzzer_0 GND	GROUND

Code

Arduino C++

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#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define TRIG_PIN 27
#define ECHO_PIN 26
#define GREEN_LED_PIN 14
#define YELLOW_LED_PIN 12
#define RED_LED_PIN 13
#define BUZZER_PIN 25
#define SDA_PIN 21
#define SCL_PIN 22
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

const int SAFE_DISTANCE_CM = 70;
const int CAUTION_DISTANCE_CM = 35;
const int STOP_DISTANCE_CM = 18;

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);
float smoothedDistance = 100;
unsigned long lastBeepMs = 0;
bool buzzerOn = false;

float readDistanceCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  unsigned long duration = pulseIn(ECHO_PIN, HIGH, 30000);
  if (duration == 0) return smoothedDistance;
  return duration / 58.0;
}

void setOutputs(float distanceCm) {
  bool safe = distanceCm > SAFE_DISTANCE_CM;
  bool caution = distanceCm <= SAFE_DISTANCE_CM && distanceCm > CAUTION_DISTANCE_CM;
  bool warning = distanceCm <= CAUTION_DISTANCE_CM;

  digitalWrite(GREEN_LED_PIN, safe ? HIGH : LOW);
  digitalWrite(YELLOW_LED_PIN, caution ? HIGH : LOW);
  digitalWrite(RED_LED_PIN, warning ? HIGH : LOW);

  if (!warning) {
    noTone(BUZZER_PIN);
    buzzerOn = false;
    return;
  }

  int interval = distanceCm <= STOP_DISTANCE_CM ? 120 : 320;
  if (millis() - lastBeepMs > interval) {
    lastBeepMs = millis();
    buzzerOn = !buzzerOn;
    if (buzzerOn) tone(BUZZER_PIN, distanceCm <= STOP_DISTANCE_CM ? 1800 : 1200);
    else noTone(BUZZER_PIN);
  }
}

void drawDisplay(float distanceCm) {
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.println("Parking sensor");
  display.setTextSize(2);
  display.setCursor(0, 18);
  display.print(distanceCm, 0);
  display.println(" cm");
  display.setTextSize(1);
  display.setCursor(0, 48);
  if (distanceCm <= STOP_DISTANCE_CM) display.println("STOP");
  else if (distanceCm <= CAUTION_DISTANCE_CM) display.println("Slow down");
  else if (distanceCm <= SAFE_DISTANCE_CM) display.println("Getting close");
  else display.println("Clear");
  display.display();
}

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(GREEN_LED_PIN, OUTPUT);
  pinMode(YELLOW_LED_PIN, OUTPUT);
  pinMode(RED_LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);

  Wire.begin(SDA_PIN, SCL_PIN);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.display();
}

void loop() {
  float reading = readDistanceCm();
  smoothedDistance = (smoothedDistance * 0.75) + (reading * 0.25);
  setOutputs(smoothedDistance);
  drawDisplay(smoothedDistance);
  delay(80);
}

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