Ultrasonic Sensor (HC-SR04)

The HC-SR04 is a widely used ultrasonic distance sensor that provides non-contact measurement from 2cm to 400cm with high accuracy and stable readings. It is highly popular in robotics and DIY electronics for obstacle avoidance and proximity sensing.

Description & Working Principle

The sensor operates on the principle of SONAR (Sound Navigation and Ranging), similar to how bats and dolphins navigate. It consists of two ultrasonic transducers: one acting as a transmitter (TX) and the other as a receiver (RX).

1. Triggering: The microcontroller sends a 10µs HIGH pulse to the Trigger (Trig) pin.

2. Emission: Upon receiving this trigger, the sensor automatically emits an 8-cycle burst of ultrasonic sound at 40 kHz.

3. Reception: These sound waves travel through the air, hit an object, and bounce back to the sensor.

4. Echo Output: The Echo pin goes HIGH immediately after the 8-cycle burst is sent and stays HIGH until the reflected sound is received. The duration of this HIGH pulse is directly proportional to the distance of the object.

Characteristics

• Non-Contact Measurement: Measures distance without physical contact with the object.

• Measuring Angle: The sensor has a detection cone of approximately 15 to 30 degrees.

• Stability: Its operation is not significantly affected by sunlight or the color of the target, unlike some infrared sensors.

• Material Sensitivity: Hard surfaces reflect sound waves best; soft materials like cloth or wool can absorb sound, leading to inaccurate readings.

Operating Parameters

Calculation Formula:

To calculate the distance in centimeters, you can use the travel time (duration) of the echo pulse:

Or simplified for Arduino code (time in microseconds):