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Ultrasonic sensor

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What is ultrasonic sensor?

Ultrasonic sensor on the turtle robot
Ultrasonic sensor connection

How does ultrasonic sensor work?

ultrasonic principle

Principle of ultrasonic sensor

Read from an ultrasonic sensor

Pin mode definition

Purpose Mode Pin on board
Emit sound (Trip) Output 12
Receive sound (Echo) Input 13 
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int pinTrip = 12;
int pinEcho = 13;
void setup() {
  pinMode(pinTrip, OUTPUT);
  pinMode(pinEcho, INPUT);
}

Distance calculation

Distance of the object in front of the ultrasonic sensor can be calculated using the time between sending and receiving the signal (sound)

d

Time between sending and receiving = time to travel for \(2d\) = \(T\) µs

Formula derivation

\[\begin{aligned} \text{distance }d & = \frac{T \text{ µs}\times \text{speed of sound}}{2}\\\\ & = \frac{T \text{ µs} \times 340 \text{ m/s}}{2}\\\\ & = T \times 10^{-6} \text{ s} \times 170 \times 10^2 \text{ cm/s}\\\\ & = 170 \times 10^{-4} \times T \text{ cm}\\\\ & \approx \frac{T}{58} \text{ cm} \end{aligned}\]

Code implementation

To implement the emission and recipient of sound and calculating the distance of the object in code,

Emit (>10µs) Receive Calculate distance 
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void loop() {
  digitalWrite(pinTrip,LOW);        //(1)
  delayMicroseconds(2);
  digitalWrite(pinTrip,HIGH);
  delayMicroseconds(12);            //(2)
  digitalWrite(pinTrip,LOW);        //(3)
  distance=pulseIn(pinEcho,HIGH);
  delay(10);                        //(4)
  distance=distance/58;             //(5)
  delay(500);
}
  1. Emit sound for 12 µs (Start)
  2. Emit sound for 12 µs (End)
  3. Receive sound (Start)
  4. Receive sound (End)
  5. Calculate distance

Serial monitor to display calculated distance

We can use the serial monitor to display the calculated distance

Enable Display 
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...
void setup() {
  ...
  Serial.begin(9600);         //(1)
}
void loop() {
  ...
  distance=distance/58;
  Serial.print("distance=");  //(2)
  Serial.print(distance);
  Serial.println("cm");       //(3)
  delay(500);
}
  1. Enable serial connection at baud rate of 9600
  2. Serial.print("text") prints out the text
  3. Serial.println("text") prints out the text and end the line, further printing will start in a new line

Combining the code

int pinTrip = 12;
int pinEcho = 13;
float distance = 0; //(1)
void setup() {
  pinMode(pinTrip, OUTPUT);
  pinMode(pinEcho, INPUT);
  Serial.begin(9600);
}
void loop() {
  digitalWrite(pinTrip,LOW);
  delayMicroseconds(2);
  digitalWrite(pinTrip,HIGH);
  delayMicroseconds(12);
  digitalWrite(pinTrip,LOW);
  distance=pulseIn(pinEcho,HIGH);
  delay(10);
  distance=distance/58;
  Serial.print("distance=");
  Serial.print(distance);
  Serial.println("cm");
  delay(500);
}
  1. Take note of this line. We need to define the variable to later save our reading from the ultrasonic sensor.

Verify and upload the code to the robot

Launch serial monitor

After the code is running on the robot, launch serial monitor from the Arduino IDE

launch serial monitor

Tools > Serial Monitor

serial monitor

Serial Monitor (Baud rate 9600)