Ultrasonic Distance Sensor

1 Principle
2 Connections
3 Code
4 Simulation

Principle

Ultrasonic sensors use the same principle bats (flying mammals) use to detect obstacles – by sending ultrasonic signals and analysing the reflection / echo
The time between sending a signal (a trigger pulse of width 10us) and receiving an echo is used to calculate the distance from an object
HC-SR04 needs +5V DC, works for obstacles at an angle <15°, for distances between 2cm – 400 cm
Practically, 3-300 cm is fairly accurate (up to 0.3cm). If it is too close or too far, no meaningful echo will be received, and the reading might show a high / inaccurate distance
Distance = (time taken from trigger to echo/2) x speed of sound
Speed of sound is about 345 m/s at 23^oC

Connections

Assuming digital pin 9 is the triggerPin and digital pin 8 is the echoPin.

Code

C++	Blocks

C++

Blocks

long readUltrasonicDistance(int triggerPin, int echoPin)
{
  pinMode(triggerPin, OUTPUT);  // Clear the trigger
  digitalWrite(triggerPin, LOW);
  delayMicroseconds(2);
 // Sets the trigger pin to HIGH state for 10 microseconds
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);
  pinMode(echoPin, INPUT);
 // Reads the echo pin, and returns the
 // sound wave travel time in microseconds
  return pulseIn(echoPin, HIGH);
}
  
void setup()
{
  Serial.begin(9600);
}
  
void loop()
{
  distanceCm = 0.01723 * readUltrasonicDistance(9, 8);
  // try to make sense of the above formula!
  Serial.println(distanceCm);
  delay(10);
}

Ultrasonic Distance Sensor

Principle

Connections

Code

Simulation