Lesson 1: Measure Distance with Sound

Wire the ultrasonic sensor, then read the distance to a book on your computer screen and check it against a ruler.

One of 9 projects in the Arduino Ultrasonic Distance & Parking Learning Kit — the parts below are from that kit.

Before you start

What you build and learn

• How the HC-SR04 measures distance with sound
• Wiring a module by its labels: VCC, TRIG, ECHO, GND
• Reading numbers in the Serial Monitor
• Why you average several readings instead of trusting one

New words

Ultrasound

Sound too high for people to hear. The HC-SR04 uses 40 kHz.

Echo

Sound that bounces back off an object.

Breadboard

A board with hidden metal strips. Parts in the same short row of holes are connected.

Rail

The long lines of holes along the edge of the breadboard: red line (+) for 5V, blue line (−) for GND.

Serial Monitor

A window in the Arduino IDE (Tools → Serial Monitor) that shows the text the UNO sends.

What this project uses

Every item is in the kit — nothing extra to buy.

UNO R3 UNO R3 Development Board ATmega328P Microcontroller with USB Cable, 5V Logic, 14 Digital I/O, 6 Analog Inputs… UNOR3

In the kit

HC-SR04 HC-SR04 Ultrasonic Distance Sensor Module for Arduino, Raspberry Pi & DIY Robotics Projects, 5V Trigger/Echo… DIY-00043

In the kit

400 tie-point breadboard 400 Tie Point Solderless Breadboard - Half Size Prototyping Circuit Board with Power Rails, for Arduino & Ele… DIY-238

In the kit

jumper wires Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212

In the kit

◇

a ruler and a flat card or book (yours)

In the kit

Build this with

Arduino Ultrasonic Distance & Parking Learning Kit

All 9 parts in one box, with this project and 8 more to build from them.

AED 85.00 See the kit Add kit to cart

Need only these parts? Order them loose · from AED 78.30 ▾

Used in this project tick what you still need

UNO R3 UNO R3 Development Board ATmega328P Microcontroller with USB Cable, 5V Logic, 14 Digital I/O, 6 Analog Inputs… UNOR3 · ×1

AED 26.39

In stock

HC-SR04 HC-SR04 Ultrasonic Distance Sensor Module for Arduino, Raspberry Pi & DIY Robotics Projects, 5V Trigger/Echo… DIY-00043 · ×1

AED 15.31

In stock

400 tie-point breadboard 400 Tie Point Solderless Breadboard - Half Size Prototyping Circuit Board with Power Rails, for Arduino & Ele… DIY-238 · ×1

AED 11.58

In stock

jumper wires Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212 · ×1

AED 25.02

In stock

Selected parts AED 78.30

Add 4 parts to cart

One of each part. Packs (resistor assortment, jumper wires) already hold more than a single build needs. a ruler and a flat card or book (yours): included in the kit, ask us for it loose. Delivery is AED 20, free on orders AED 100+.

Connections

Unplug USB before you change any wire. Pin names are the labels printed on the board.

Step by step

One thing at a time. Tick nothing off until it matches the diagram.

1. Unplug the USB cable from the computer.Watch out: Always unplug the USB cable before you add, move or remove a wire.
2. Put the breadboard next to the UNO. Find the red (+) and blue (−) lines along its edge: those are the rails.
3. Connect a jumper wire from the UNO 5V pin to the + rail, and one from a UNO GND pin to the − rail.Watch out: Never join the + rail straight to the − rail.
4. Push the HC-SR04 into the breadboard near one end, with its two round "eyes" facing out over the edge and each of its 4 pins in its own row.Watch out: Read the labels printed by the pins: VCC, Trig, Echo, Gnd. Some sensors print them in a different order.
5. Wire VCC to the + rail, GND to the − rail, TRIG to UNO pin 9 and ECHO to UNO pin 10.
6. Check every wire against the diagram and the table, then plug the USB cable back in.Watch out: If anything gets hot or smells, unplug straight away.
7. Copy the Lesson 1 code below into the Arduino IDE and click Upload (→).
8. Open Tools → Serial Monitor and set the speed to 9600 baud.
9. Lay a ruler on the table from the front of the sensor. Hold a book upright at 10, 20, 30 and 50 cm and write down the number shown each time.

Sketch for this project

Written for the board in the kit. Copy it into the Arduino IDE; change the pin numbers if you wire it differently.

/*
  DIY KIT - Arduino Ultrasonic Distance & Parking Learning Kit
  Lesson 1 of 9: Measure Distance with Sound

  WIRING (unplug the USB cable before you wire)
    HC-SR04 VCC  -> 5V   (+ rail)
    HC-SR04 TRIG -> UNO pin 9
    HC-SR04 ECHO -> UNO pin 10
    HC-SR04 GND  -> GND  (- rail)

  WHAT SHOULD HAPPEN
    Open Tools > Serial Monitor and set it to 9600 baud. Twice a second a
    new line shows the distance to whatever is in front of the sensor, and
    how many of the 5 pings came back. Hold a book in front of the sensor
    and compare the number with a ruler.
*/

const int TRIG_PIN = 9;    // we send the "click" from here
const int ECHO_PIN = 10;   // the sensor answers on this pin

const int SAMPLES = 5;                         // pings per line - try 1 and see the numbers jump
const unsigned long ECHO_TIMEOUT_US = 30000;   // give up after 30 ms (about 5 m there and back)
const int MIN_CM = 2;                          // closer than this the sensor cannot measure
const int MAX_CM = 400;                        // further than this is out of range

int lineNumber = 0;

// One measurement in centimetres, or 0 if no echo came back.
long readOnceCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);   // a 10-microsecond pulse starts one measurement
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // pulseIn() times how long ECHO stays HIGH: the sound's trip there and back.
  unsigned long us = pulseIn(ECHO_PIN, HIGH, ECHO_TIMEOUT_US);
  if (us == 0) return 0;          // no echo

  long cm = us / 58;              // sound needs about 58 microseconds per cm, there and back
  if (cm < MIN_CM || cm > MAX_CM) return 0;
  return cm;
}

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.begin(9600);
  Serial.println("Lesson 1: Measure Distance with Sound");
  Serial.println("line, distance_cm, echoes (out of 5)");
}

void loop() {
  long total = 0;
  int echoes = 0;

  for (int i = 0; i < SAMPLES; i++) {
    long cm = readOnceCm();
    if (cm > 0) {             // only count pings that came back
      total = total + cm;
      echoes = echoes + 1;
    }
    delay(60);                // let the last echo die away before the next ping
  }

  lineNumber = lineNumber + 1;
  Serial.print(lineNumber);
  Serial.print(", ");
  if (echoes > 0) {
    long average = total / echoes;  // the average of the pings that came back (whole cm)
    Serial.print(average);
  } else {
    Serial.print("no echo");
  }
  Serial.print(", ");
  Serial.println(echoes);

  delay(200);
}

Upload it

1. Click Copy (or Download .ino and open the file).
2. In the Arduino IDE choose File → New Sketch, select everything in it and paste.
3. Check the bottom of the window says Arduino Uno and your port (Start here, step 5).
4. Click Upload (the → arrow) and wait for Done uploading.

How the code works

Change it and see

What you should see or hear

• A title line, then a new line about twice a second, like 7, 30, 5: line number, distance in cm, echoes out of 5.
• With a book 10-50 cm away, the distance is usually within a few cm of the ruler.
• Point it at the ceiling or an open space and you may see "no echo, 0".

If it doesn't work

Small experiment

Measure the same book at 30 cm five times, moving it away and back each time. How far apart are your five numbers?

Check what you learned

Next

• Lesson 2 adds three LEDs that show how close the book is. Leave the sensor where it is.

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