Ultrasonic Sensor HY-SRF05, 5 Pins, 2–450 cm, 5V

The HY-SRF05 ultrasonic sensor measures the distance to an obstacle without physical contact, using an ultrasonic transmitter and receiver mounted on the same PCB. It is one of the most widely used modules for obstacle-avoiding robots, parking systems and educational distance-measuring projects, thanks to its simple wiring and its compatibility with the HC-SR04.

In this tutorial you will connect the module to an Arduino Uno in standard mode, with separate TRIG and ECHO pins, and write a simple program that reads the distance and displays it on the serial monitor.

How it works:

The module starts a measurement when it receives a HIGH pulse of at least 10 microseconds on the TRIG pin. When it receives this pulse, the HY-SRF05 automatically sends a burst of eight ultrasonic pulses at 40 kHz and waits for them to bounce off the obstacle and return to the receiver.

During this whole time, the ECHO pin stays HIGH, and the duration of the HIGH state is exactly the round-trip time of the sound wave. The code measures this duration in microseconds with the pulseIn function and calculates the distance with the formula Distance in centimeters equals duration multiplied by 0.034 and divided by two, where 0.034 is the speed of sound of about 340 m/s expressed in cm per microsecond.

You must leave at least 60 ms between two measurements, so that the echoes left over from the previous pulse are not mistaken for the next measurement.

What you need:

• 1 x Ultrasonic Sensor HY-SRF05, 5 Pins, 2–450 cm, 5V
• 1 x Placa dezvoltare Uno R3 cu Wifi ESP8266, compatibila Arduino
• 4 x 40 Fire Dupont 20cm, Tata-Mama

Wiring:

The module is powered at 5 VDC and uses 5V TTL logic levels, directly compatible with the Arduino Uno. Connect VCC to 5V and GND to the board's ground, then connect TRIG to a digital pin configured as output and ECHO to a digital pin configured as input. The OUT pin stays unconnected, so that the module works in standard mode, with separate TRIG and ECHO.

The code:

Upload the program below in the Arduino IDE, with the board set to Arduino Uno and the correct serial port selected.

// HY-SRF05 Ultrasonic Distance Sensor with Arduino Uno
// Standard mode: separate TRIG and ECHO pins, OUT pin left unconnected
const int trigPin = 9;   // TRIG pin connected to Arduino digital pin D9
const int echoPin = 10;  // ECHO pin connected to Arduino digital pin D10
void setup() {
  Serial.begin(9600);     // Start serial communication at 9600 baud
  pinMode(trigPin, OUTPUT); // TRIG pin sends the trigger pulse
  pinMode(echoPin, INPUT);  // ECHO pin reads the returning pulse
}
void loop() {
  // Make sure the trigger pin is low before starting
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  // Send a 10 microsecond HIGH pulse to start the measurement
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  // Measure how long the echo pin stays HIGH, in microseconds
  // timeout of 30000 us avoids blocking if no echo is received
  long duration = pulseIn(echoPin, HIGH, 30000);
  // Convert the duration into distance in centimeters
  // speed of sound is about 0.034 cm per microsecond
  // divide by 2 because the sound travels to the object and back
  float distance = duration * 0.034 / 2.0;
  if (duration == 0) {
    Serial.println("No echo received, check the wiring or the object distance");
  } else {
    Serial.print("Distance: ");
    Serial.print(distance);
    Serial.println(" cm");
  }
  // Wait before the next measurement, more than the 60 ms minimum
  delay(100);
}

How the code works:

At the beginning of the program, the constants trigPin and echoPin are defined, set to D9 and D10 respectively, exactly the pins used in the wiring diagram.

In the setup function, serial communication is initialized at 9600 baud with Serial.begin, and trigPin is configured as OUTPUT and echoPin as INPUT using the pinMode function.

In the loop function, the program first sets trigPin to LOW for two microseconds, then raises it to HIGH for 10 microseconds using digitalWrite and delayMicroseconds, which is exactly the trigger pulse required by the module.

The duration of the HIGH signal on echoPin is read with the pulseIn function and stored in the variable duration, after which the distance is calculated with the formula distance equals duration times 0.034 divided by two and is displayed on the serial monitor with Serial.print.

At the end of each loop, a 100 ms delay ensures an interval longer than the recommended minimum of 60 ms between two consecutive measurements.

Result:

Open the serial monitor in the Arduino IDE at 9600 baud. You should see the distance displayed in centimeters every 100 ms, with the value changing as you move an object closer to or farther from the sensor.

Distance: 23.45 cm
Distance: 23.41 cm
Distance: 22.98 cm
Distance: 45.12 cm
Distance: 44.87 cm
No echo received, check the wiring or the object distance
Distance: 102.33 cm
Distance: 101.90 cm

Common problems:

If nothing appears on the serial monitor, check that you have selected the correct COM port and the Arduino Uno board in the Arduino IDE, and that the serial monitor speed is set to 9600 baud, the same value used in Serial.begin.

If the displayed distance is always 0 or a very large number, check that echoPin is correctly configured as INPUT and that the ECHO wire is firmly connected to pin D10, with no interrupted contact.

If the values are unstable or jump suddenly between very different numbers, move away any other ultrasonic sensors pointing in the same direction and make sure the obstacle is a hard, flat surface placed perpendicular to the sensor.

If the module does not respond at all, check the power polarity. The VCC pin must be connected to 5V and not to 3.3V, otherwise the sensor will not start the measurement.

If you use a board with 3.3V logic instead of the Arduino Uno, keep in mind that the 5V ECHO signal must go through a voltage divider before reaching the board's input pin, otherwise you risk damaging the input.

Limitations and tips:

The HY-SRF05 measures reliably between 2 cm and 450 cm, with a detection angle of at most 15 degrees, which means that thin objects or objects placed to the side of the sensor axis may not be detected correctly. Soft materials, such as fabrics or sponge, absorb part of the ultrasonic wave and can reduce the maximum detection distance.

For projects with fewer free pins on the microcontroller, you can use the module's single-pin mode by connecting OUT to GND and using only the TRIG pin to send the pulse and read the echo, but the standard two-pin mode remains the safest for the first tests.

Once the setup works reliably, you can expand it with several HY-SRF05 modules pointing in different directions for a robot that avoids obstacles on multiple sides, or you can integrate it into a tank level measuring system.