1. Ultrasonic Distance Sensor

2. How it Works
The sensor emits short bursts of sound, and listens for the echo off nearby objects
By measuring the time of flight, distance can be computed

3. When it doesn’t work
When waves are not reflected back towards the sensor

4. Specifications
An ultrasonic sensor comes with a chart indicating how far and wide its waves will travel
They are not laser beams, and objects not directly in front can still reflect waves back
For this sensor the waves travel ±20°
And up to 7.5 feet

5. Wiring
An ultrasonic sensor contains 2 sensors, a speaker and a microphone
The speaker is an OUTPUT
The microphone is an INPUT
There are also connections for 5v and GND

6. Distance = Speed x Time Example Miles = MPH x Hours Computing Distance
The sensor will give us the time for the round trip
Multiplying the time by the speed of sound, and divide by 2 to calculate for one way
The speed of sound is 761 MPH, or 1/74 inches per microsecond

7. Code
void setup() {
Serial.begin(9600);
pinMode(12, OUTPUT);
pinMode(11, INPUT); }
void loop() { long duration, inches; digitalWrite(12, LOW); delayMicroseconds(2); digitalWrite(12, HIGH); delayMicroseconds(5); digitalWrite(12, LOW);
duration = pulseIn(11, HIGH);
inches = duration / 74 / 2;
Serial.print(inches);
Serial.println("in "); }
By setting pin 12 to HIGH, the speaker sends a 40kHz (ultrasonic) burst of sound out its “speaker”
The sound burst reflects off something and returns to the microphone; the microphone then sets INPUT pin 11 to HIGH.
The pulseIn command measures the time of flight (the time it took the wave to travel back to the microphone and turn pin 11 HIGH).
Multiplying TIME x SPEED (1/74) and dividing by 2 gives us the distance traveled

8. Complete the Ultrasonic Distance Sensor
LAB
Complete the Ultrasonic Distance Sensor
Lab in Unit 11