Overview of Ultrasonic Sensor
The Ultrasonic Module HC-SR04 operates on the principle of SONAR and RADAR, making it useful for measuring the distance of an object within the range of 2 cm to 400 cm. The module consists of four pins:
- VCC
- GND
- Trig
- Echo
When a pulse of 10 µs or more is applied to the Trig pin, the module generates 8 pulses at 40 kHz. After the pulse, the Echo pin is set high by the module’s control circuit. The Echo pin stays high until the transmitted pulses are reflected back to the module.
The duration for which the Echo pin remains high corresponds to the time it takes for the ultrasonic sound to travel to the object and return. Using this time and the speed of sound in air, we can calculate the distance to the object using the simple formula:
Distance = (Speed of Sound × Time) / 2
For further details on using the Ultrasonic Module HC-SR04, refer to the “Ultrasonic Module HC-SR04” section in the Sensors and Modules.
Application
Let’s design an application to measure the distance to an object by interfacing the Ultrasonic Module HC-SR04 with an Arduino and displaying the distance on the Serial Monitor.
In this application, we will use the Ping example that comes with the Arduino IDE in the Sensors library.
You can find this example in:
File -> Examples -> Sensors -> Ping.
Connection Diagram of Ultrasonic Sensor HC-SR04 with Arduino
Ultrasonic Sensor HC-SR04 interfaced with Arduino
Distance Measurement Code using Ultrasonic Sensor HC-SR04 and Arduino Uno
/*
Ping))) Sensor
This sketch reads a PING))) ultrasonic rangefinder and returns the distance
to the closest object in range. To do this, it sends a pulse to the sensor to
initiate a reading, then listens for a pulse to return. The length of the
returning pulse is proportional to the distance of the object from the sensor.
The circuit:
- +V connection of the PING))) attached to +5V
- GND connection of the PING))) attached to ground
- SIG connection of the PING))) attached to digital pin 7
created 3 Nov 2008
by David A. Mellis
modified 30 Aug 2011
by Tom Igoe
This example code is in the public domain.
http://www.arduino.cc/en/Tutorial/Ping
*/
// this constant won't change. It's the pin number of the sensor's output:
const int pingPin = 7;
void setup() {
// initialize serial communication:
Serial.begin(9600);
}
void loop() {
// establish variables for duration of the ping, and the distance result
// in inches and centimeters:
long duration, inches, cm;
// The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
pinMode(pingPin, OUTPUT);
digitalWrite(pingPin, LOW);
delayMicroseconds(2);
digitalWrite(pingPin, HIGH);
delayMicroseconds(5);
digitalWrite(pingPin, LOW);
// The same pin is used to read the signal from the PING))): a HIGH pulse
// whose duration is the time (in microseconds) from the sending of the ping
// to the reception of its echo off of an object.
pinMode(pingPin, INPUT);
duration = pulseIn(pingPin, HIGH);
// convert the time into a distance
inches = microsecondsToInches(duration);
cm = microsecondsToCentimeters(duration);
Serial.print(inches);
Serial.print("in, ");
Serial.print(cm);
Serial.print("cm");
Serial.println();
delay(100);
}
long microsecondsToInches(long microseconds) {
// According to Parallax's datasheet for the PING))), there are 73.746
// microseconds per inch (i.e. sound travels at 1130 feet per second).
// This gives the distance travelled by the ping, outbound and return,
// so we divide by 2 to get the distance of the obstacle.
// See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
return microseconds / 74 / 2;
}
long microsecondsToCentimeters(long microseconds) {
// The speed of sound is 340 m/s or 29 microseconds per centimeter.
// The ping travels out and back, so to find the distance of the object we
// take half of the distance travelled.
return microseconds / 29 / 2;
}Function Used
pulseIn()The pulseIn() function reads the duration of a pulse (either HIGH or LOW) on a pin.
For example, if the value is HIGH, pulseIn() waits for the pin to transition from LOW to HIGH, starts timing, then waits for the pin to go LOW again and stops timing. It returns the length of the pulse in microseconds, or 0 if no complete pulse is received within the specified timeout.
For example:
pulseIn(7, HIGH);