DIY Ultrasound Distance Meter with Arduino

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Introduction

In this recipe, I'll take you through the step-by-step process of building and programming your own ultrasound distance meter. We'll cover the basics of how the technology works, how to connect the components, and how to write the code to bring it all together. By the end of this recipe, you'll have a fully functional distance meter that you can use in your own projects, and a deeper understanding of the possibilities of ultrasound technology.



4-Digit 7 Segment LED display


A typical 4-digit 7-segment LED display consists of 12 pins, which can be divided into two main categories:

  • Segment Pins: 8 pins are dedicated to controlling the individual LEDs that make up each 7-segment display. These pins are labeled A-G and DP (decimal point), and are responsible for illuminating the corresponding segments of each digit.
  • Digit Pins: The remaining 4 pins represent each of the 4 digits (D1-D4) in the display module. These pins are used to control the common cathode connection point for each digit, allowing each digit to be turned on or off independently.


Multiplexing Technique

The display module uses a multiplexing technique, where each segment shares the same anode connection points. This means that each digit has its own common cathode connection point, which enables independent control over each digit. This technique significantly reduces the number of microcontroller pins required to control the display, from 32 to just 11 or 12.


Common Anode or Common Cathode Configuration

The display module can be configured as either common anode or common cathode. In a common anode configuration, the anode connection points are shared among the segments, while in a common cathode configuration, the cathode connection points are shared among the digits. This configuration allows for efficient control of the display using a minimal number of microcontroller pins.


Ultrasound Meter

The HC-SR04 is an ultrasonic distance sensor that works by emitting high-frequency sound waves and measuring the time it takes for them to bounce back from an object. It consists of a transmitter and receiver. The transmitter sends out a 40 kHz ultrasonic wave, which hits an object and bounces back to the receiver. The sensor then calculates the distance based on the time difference between sending and receiving the wave, using the speed of sound.


Ingredients:


  • 1 x Arduino Board (e.g. Arduino Uno or Arduino Nano)
  • 1 x Ultrasound Sensor HC-SR04
  • 1 x Breadboard
  • 1 x USB Cable (for connecting Arduino to computer)
  • 1 x Power Source (e.g. USB power or battery pack)
  • 1 x 4 digit 7 segment display for displaying distance readings
  • Jumper Wires (male-to-male and male-to-female)
  • 8 x 220 ohm resistors.


Preparation:


Sketch





Code

#include <TimerOne.h>

#define echoPin 0 // attach pin D2 Arduino to pin Echo of HC-SR04
#define trigPin 1 // attach pin D3 Arduino to pin Trig of HC-SR04

long duration; // Variable to store time taken to the pulse to reach receiver
int distance; // Variable to store distance calculated using formula

// 7-segment display pins
int a = 2;
int b = 3;
int c = 4;
int d = 5;
int e = 6;
int f = 7;
int g = 8;
int p = 9;
int d4 = 10;
int d3 = 11;
int d2 = 12;
int d1 = 13;

long n = 0; // n represents the value displayed on the LED display (e.g., 0000)
int del = 2; // Set delay to control display flicker
unsigned long previousMillis = 0; // Store last update time for display
const long interval = 5; // Interval to update the display (in ms)

volatile long newDistance = 0; // This will hold the latest measured distance
volatile bool distanceUpdated = false; // Flag to indicate that distance is updated

void setup()
{
pinMode(trigPin, OUTPUT); // Sets the trigPin as an OUTPUT
pinMode(echoPin, INPUT); // Sets the echoPin as an INPUT

// Set all the pins of the LED display as output
pinMode(d1, OUTPUT);
pinMode(d2, OUTPUT);
pinMode(d3, OUTPUT);
pinMode(d4, OUTPUT);
pinMode(a, OUTPUT);
pinMode(b, OUTPUT);
pinMode(c, OUTPUT);
pinMode(d, OUTPUT);
pinMode(e, OUTPUT);
pinMode(f, OUTPUT);
pinMode(g, OUTPUT);
pinMode(p, OUTPUT);

Timer1.initialize(100000); // Set a timer of length 100000 microseconds (0.1 sec)
Timer1.attachInterrupt(add); // Attach the interrupt service routine
}

void loop()
{
unsigned long currentMillis = millis();

// Update display at a non-blocking interval
if (currentMillis - previousMillis >= interval) {
previousMillis = currentMillis;

clearLEDs(); // Clear the display
pickDigit(0); // Light up 7-segment display d1
pickNumber((n / 1000)); // Get the value of thousand
delay(del); // Small delay to avoid flicker

clearLEDs(); // Clear the display
pickDigit(1); // Light up 7-segment display d2
pickNumber((n % 1000) / 100); // Get the value of hundred
delay(del); // Small delay

clearLEDs(); // Clear the display
pickDigit(2); // Light up 7-segment display d3
pickNumber(n % 100 / 10); // Get the value of ten
delay(del); // Small delay

clearLEDs(); // Clear the display
pickDigit(3); // Light up 7-segment display d4
pickNumber(n % 10); // Get the value of single digit
delay(del); // Small delay
}

// Only update 'n' with the latest distance if it was updated in the interrupt
if (distanceUpdated) {
n = newDistance;
distanceUpdated = false; // Reset the flag
}
}

// Light up a specific 7-segment display digit
void pickDigit(int x)
{
digitalWrite(d1, LOW);
digitalWrite(d2, LOW);
digitalWrite(d3, LOW);
digitalWrite(d4, LOW);

switch (x)
{
case 0: digitalWrite(d1, HIGH); break;
case 1: digitalWrite(d2, HIGH); break;
case 2: digitalWrite(d3, HIGH); break;
case 3: digitalWrite(d4, HIGH); break;
}
}

// Display numbers 0-9 on the 7-segment display
void pickNumber(int x)
{
switch (x)
{
case 0: zero(); break;
case 1: one(); break;
case 2: two(); break;
case 3: three(); break;
case 4: four(); break;
case 5: five(); break;
case 6: six(); break;
case 7: seven(); break;
case 8: eight(); break;
case 9: nine(); break;
}
}

// Clear the 7-segment display
void clearLEDs()
{
digitalWrite(a, LOW);
digitalWrite(b, LOW);
digitalWrite(c, LOW);
digitalWrite(d, LOW);
digitalWrite(e, LOW);
digitalWrite(f, LOW);
digitalWrite(g, LOW);
digitalWrite(p, HIGH);
}

// Define each number from 0 to 9 for 7-segment display
void zero() { digitalWrite(a, LOW); digitalWrite(b, LOW); 
digitalWrite(c, LOW); digitalWrite(d, LOW); digitalWrite(e, LOW); 
digitalWrite(f, LOW); digitalWrite(g, HIGH); }
void one() { digitalWrite(a, HIGH); digitalWrite(b, LOW); 
digitalWrite(c, LOW); digitalWrite(d, HIGH); digitalWrite(e, HIGH); 
digitalWrite(f, HIGH); digitalWrite(g, HIGH); }
void two() { digitalWrite(a, LOW); digitalWrite(b, LOW); 
digitalWrite(c, HIGH); digitalWrite(d, LOW); digitalWrite(e, LOW); 
digitalWrite(f, HIGH); digitalWrite(g, LOW); }
void three() { digitalWrite(a, LOW); digitalWrite(b, LOW); 
digitalWrite(c, LOW); digitalWrite(d, LOW); digitalWrite(e, HIGH); 
digitalWrite(f, HIGH); digitalWrite(g, LOW); }
void four() { digitalWrite(a, HIGH); digitalWrite(b, LOW); 
digitalWrite(c, LOW); digitalWrite(d, HIGH); digitalWrite(e, HIGH); 
digitalWrite(f, LOW); digitalWrite(g, LOW); }
void five() { digitalWrite(a, LOW); digitalWrite(b, HIGH); 
digitalWrite(c, LOW); digitalWrite(d, LOW); digitalWrite(e, HIGH); 
digitalWrite(f, LOW); digitalWrite(g, LOW); }
void six() { digitalWrite(a, LOW); digitalWrite(b, HIGH); 
digitalWrite(c, LOW); digitalWrite(d, LOW); digitalWrite(e, LOW); 
digitalWrite(f, LOW); digitalWrite(g, LOW); }
void seven() { digitalWrite(a, LOW); digitalWrite(b, LOW); 
digitalWrite(c, LOW); digitalWrite(d, HIGH); digitalWrite(e, HIGH); 
digitalWrite(f, HIGH); digitalWrite(g, HIGH); }
void eight() { digitalWrite(a, LOW); digitalWrite(b, LOW); 
digitalWrite(c, LOW); digitalWrite(d, LOW); digitalWrite(e, LOW); 
digitalWrite(f, LOW); digitalWrite(g, LOW); }
void nine() { digitalWrite(a, LOW); digitalWrite(b, LOW); 
digitalWrite(c, LOW); digitalWrite(d, LOW); digitalWrite(e, HIGH); 
digitalWrite(f, LOW); digitalWrite(g, LOW); }

// Interrupt function to read the distance
void add()
{
digitalWrite(trigPin, LOW);
delayMicroseconds(2); // Ensure the trigPin has been low for at least 2 µs
digitalWrite(trigPin, HIGH);
delayMicroseconds(10); // Trigger pulse width of 10 µs
digitalWrite(trigPin, LOW);

// Measure the duration of the pulse received
duration = pulseIn(echoPin, HIGH);
newDistance = duration * 0.0344 / 2; // Calculate the distance in cm

distanceUpdated = true; // Set the flag to indicate that new data is available
}

Serving:

The 4 digit display will show the distance in cm, but you can also use a LCD display for this purpose. There are endless possibilities.  On this example, the circuit has been transformed into a fixed board to have my own portable distance meter.




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