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 23oC
Connections
Assuming digital pin 9 is the triggerPin and digital pin 8 is the echoPin.
Code
| C++ | Blocks |
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| Code Block |
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| language | cpp |
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| theme | Confluence |
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| linenumbers | true |
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| 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);
}]] ></ac:plain-text-body></ac:structured-macro></div></td><td><div class="content-wrapper"><p><ac:image ac:width="700"><ri:attachment ri:filename="image2020-1-20_14-54-15.png" /></ac:image></p></div></td></tr></tbody></table><p><br /></p><h3>Simulation</h3><p><ac:image ac:width="850"><ri:attachment ri:filename="image2020-1-20_14-51-24.png" /></ac:image></p><h3>Screencast</h3><p><ac:structured-macro ac:name="widget" ac:schema-version="1" ac:macro-id="d71c5279-42ca-41f6-87e4-e5aa3be42cde"><ac:parameter ac:name="url"><ri:url ri:value="http://youtube.com/watch?v=l3WxIxFNTt8" /></ac:parameter></ac:structured-macro></p> |
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