Using the HC-SR04 Ultrasonic Distance Sensor with Arduino

📦 Buy the HC-SR04 here: HC-SR04 Ultrasonic Distance Sensor on Amazon
– https://amzn.to/3HsNIz2
📦 Buy the LCD-here: 16×2 LCD Screen on Amazon
– https://amzn.to/4fJYIVo

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1. Overview & Goals

This project shows how to interface the HC-SR04 ultrasonic sensor with an Arduino Uno to measure distances.
We will:

• Wire the HC-SR04 to the Arduino.
• Trigger the sensor to send ultrasonic pulses.
• Measure the echo pulse width.
• Convert that pulse width to a distance in centimeters.
• Display the readings on both the Serial Monitor and a 16×2 LCD.

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2. System Architecture

Block Diagram

+--------------------+         +----------------+
|   Arduino Uno      |<------->|   LCD (16x2)   |
|   (5V MCU)         |         +----------------+
|                    |
|  [Trig] ----> HC-SR04 Trigger Pin
|  [Echo] <---- HC-SR04 Echo Pin
|                    |
+--------------------+

• Arduino Uno: Controls sensor and processes data.
• HC-SR04: Sends ultrasonic burst and measures return time.
• LCD 16×2 (I²C): Displays measured distance.
• Serial Monitor: Debug and monitoring.

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3. Bill of Materials (BOM)

Item	Part Number / Description	Vendor
MCU	Arduino Uno R3	Amazon
Sensor	HC-SR04 Ultrasonic Module	Amazon
Display	16×2 LCD with I²C Backpack (PCF8574)	Amazon / AliExpress
Wires	Male-to-Female Dupont Jumper Wires	Amazon
Breadboard	Standard Solderless Breadboard	Amazon
Power	USB cable for Arduino	Included

Specs to note:

• HC-SR04 operating voltage: 5V
• Trigger input: 10 µs pulse
• Echo output: Pulse width proportional to distance

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4. Hardware Setup

Pin Connections

HC-SR04 Pin	Arduino Uno Pin
VCC	5V
GND	GND
Trig	D9
Echo	D10

LCD Pin (via I²C)	Arduino Uno Pin
VCC	5V
GND	GND
SDA	A4
SCL	A5

Notes

• Ensure echo pin does not exceed 5V (safe on Uno, but level shifting needed for 3.3V MCUs).
• Keep sensor face perpendicular to object surface for best results.
• Maximum range: ~4m.

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5. Firmware / Software Bring-Up

Toolchain

• Install Arduino IDE from arduino.cc.
• Select Arduino Uno board and correct COM port.

Libraries

Install the LiquidCrystal_I2C library via Library Manager:

Sketch → Include Library → Manage Libraries → Search "LiquidCrystal I2C" → Install

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6. Arduino Code

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

#define TRIG_PIN 9
#define ECHO_PIN 10

LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  Serial.begin(9600);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);

  lcd.init();
  lcd.backlight();

  lcd.setCursor(0,0);
  lcd.print("HC-SR04 Test");
  delay(1000);
}

void loop() {
  // Trigger the sensor
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Measure echo pulse
  long duration = pulseIn(ECHO_PIN, HIGH);

  // Convert to distance (cm)
  float distance = duration * 0.0343 / 2;

  // Print results
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("Distance:");
  lcd.setCursor(0,1);
  lcd.print(distance);
  lcd.print(" cm");

  delay(500);
}

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7. Integration & Testing

Serial Monitor

• Open Serial Monitor at 9600 baud.
• You should see distance values updating every 0.5s.

LCD

• LCD should show: Distance: XX.XX cm

Test Cases

• Place a flat object at 10 cm, 20 cm, 50 cm.
• Verify readings are within ±1 cm.

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8. Performance & Reliability Notes

• HC-SR04 accuracy: ~3 mm in ideal conditions.
• Avoid measuring soft/angled surfaces → poor reflections.
• If readings are unstable, add 10 µF capacitor across VCC & GND.
• For battery-powered setups, reduce measurement frequency to save power.

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9. Next Steps & Extensions

• Add buzzer alert when object < threshold distance.
• Log data to SD card.
• Display graph on OLED or web dashboard via ESP8266/ESP32.
• Use multiple sensors for obstacle avoidance in robots.

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