📡 What is the HC-SR04?

The HC-SR04 is an ultrasonic distance sensor that measures the distance to objects using high-frequency sound waves (ultrasound). Think of it as a bat-like echo radar! 🦇

🧠 How It Works

1. The TRIG pin sends a short pulse (10 microseconds).
2. The module emits an ultrasonic burst at 40 kHz.
3. If the sound wave hits an object, it reflects back.
4. The ECHO pin goes HIGH for the duration it took the wave to bounce back.
5. Arduino measures that time and calculates the distance.

📐 Distance Formula

distance_cm = (duration * 0.0343) / 2;

• Speed of sound: ~343 m/s = 0.0343 cm/µs
• Divide by 2 because the sound travels to the object and back

🔌 Pinout

⚙️ Arduino Code Example

const int trigPin = 9;
const int echoPin = 10;

void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  // Clear the trigger
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Send a 10 µs pulse
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the echo time
  long duration = pulseIn(echoPin, HIGH);

  // Calculate the distance
  float distance = duration * 0.0343 / 2;

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

  delay(500);
}

✅ Pros

• Super cheap 💰
• Easy to use
• Accurate enough for most robotics
• Works on 5V — no logic level conversion needed

⚠️ Limitations

• Doesn’t work well with soft or absorbent surfaces (like cloth)
• Can’t detect transparent objects (like glass)
• Has a minimum range of ~2 cm
• Noisy environments can cause false readings

🤖 Use Cases

• Obstacle-avoiding robots 🚗📡
• Auto water level sensors
• DIY radar systems
• Motion detection

Wanna go further? I can show you:

• A real robot project using HC-SR04
• 3D-printed mount for it
• Comparison vs VL53L0X laser sensor
  Just say the word! 🚀📏