Original source: https://arduinogetstarted.com/tutorials/arduino-ultrasonic-sensor
Ultrasonic sensor HC-SR04 is used to measure the distance to an object by using ultrasonic waves.
The ultrasonic sensor HC-SR04 includes four pins:
- VCC pin needs to be connected to VCC (5V)
- GND pin needs to be connected to GND (0V)
- TRIG pin this pin receives the control signal (pulse) from Arduino.
- ECHO pin this pin sends a signal (pulse) to Arduino. Arduino measures the duration of pulse to calculate distance.
This section is the in-depth knowledge. DON'T worry if you don't understand. Ignore this section if it overloads you, and come back in another day. Keep reading the next sections.
- Micro-controller: generates a 10-microsecond pulse on the TRIG pin.
- The ultrasonic sensor automatically emits the ultrasonic waves.
- The ultrasonic wave is reflected after hitting an obstacle.
- The ultrasonic sensor:
- Detects the reflected ultrasonic wave.
- Measures the travel time of the ultrasonic wave.
- Ultrasonic sensor: generates a pulse to the ECHO pin. The duration of the pulse is equal to the travel time of the ultrasonic wave.
- Micro-controller measures the pulse duration in the ECHO pin, and then calculate the distance between sensor and obstacle.
To get distance from the ultrasonic sensor, we only need to do two steps (1 and 6 on How It Works part)
- Generates a 10-microsecond pulse on TRIG pin
- Measures the pulse duration in ECHO pin, and then calculate the distance between sensor and obstacle
- The travel time of the ultrasonic wave (µs): travel_time = pulse_duration
- The speed of the ultrasonic wave: speed = SPEED_OF_SOUND = 340 m/s = 0.034 cm/µs
- The travel distance of the ultrasonic wave (cm): travel_distance = speed × travel_time = 0.034 × pulse_duration
- The distance between sensor and obstacle (cm): distance = travel_distance / 2 = 0.034 × pulse_duration / 2 = 0.017 × pulse_duration
Arduino's pins can generate a 10-microsecond pulse and measure the pulse duration. Therefore, we can get the distance from the ultrasonic sensor by using two Arduino's pins:
- One pin is connected to TRIG PIN to generate 10µs pulse to TRIG pin of the sensor
- Another pin is connected to ECHO PIN measure pulse from the sensor
Image is developed using Fritzing
- How to generate a 10-microsecond pulse in Arduino's pin, for example, pin 9:
- How to measures the pulse duration (µs) in Arduino's pin, for example, pin 8:
duration_us = pulseIn(8, HIGH);
- How to calculate distance (cm):
distance_cm = 0.017 * duration_us;
(See Code Session)
- Download or copy the above code and open with Arduino IDE
- Click Upload button on Arduino IDE to upload code to Arduino
- Open Serial Monitor
- Move your hand in front of the ultrasonic sensor
- See the distance from the sensor to your hand on Serial Monitor