Ultrasonic Range Sensor

Introduction

SRF04 ultrasonic distance sensor provides non-contact distance sensing function in the range of 3cm ~ 400cm with accuracy up to 0.3mm. This module has a stable performance, high distance measurement accuracy, and compact-size, and it’s simple and easy to use.

Specfication

Product Model	SRF-04
Operational Voltage	DC 5V
Static Current	2mA
Working Frequency	40Hz
Distance Measurement Range	3cm – 400cm
Measurement Angle	15°
Measurement Accuracy	0.3mm
Output Voltage	H – 5V L – 0V

Interface Definitions

PIN	Function
1 VCC	Power Source
2 ECHO	Signal Output
3 TRIG	Trigger Signal Input
4 NC	No Connection
5 GND	Ground

Dimensions

Notes

(1) This module should not be connected with power on, and if it’s necessary to do this, the module GND pin should be connected to ground first. Otherwise the module may not be able to work properly.

(2) When measuring distance, the area of the object should not be less than 0.5 square meters, and its surface need to be smooth enough. Otherwise it will affect the measurement results.

Application

Operational Principle of Module

• (1) Use the IO (TRIG) to trigger the distance measurement, and the trigger need provide at least 10us of high level signal.
• (2) The module automatically sends eight 40kHz square waves, and automatically detects whether a signal is returned.
• (3) If a signal is returned, a high level signal will be output through the IO (ECHO) pin, and the high level time is equal to the interval between emitting ultrasonic wave and receiving the returned signal. The distance calculation formula is as below. (The suggested measurement cycle is greater than 60ms, in order to avoid the transmission signal's impact on the returned signal.)

Distance (unit: m) = high-level voltage time (unit: s) * speed of sound (340 m/s) / 2

or

Distance (unit: mm) = high-level voltage time (unit: us) / 58

or

Distance (unit: inch) = high-level voltage time (unit: us) / 148

Ultra Sonic Timing Diagram

Arduino Duemilanove Example Codes

<syntaxhighlight lang="c"> const int pingPin = 7; const int start_signal = 8; void setup() {

 Serial.begin(9600);

} void loop() {

 long duration, inches, cm;
 pinMode(pingPin, OUTPUT);
 pinMode(start_signal, OUTPUT);
 digitalWrite(start_signal, HIGH);
 delayMicroseconds(20);
 digitalWrite(start_signal, LOW);
 digitalWrite(pingPin, LOW);
 delayMicroseconds(2);
 digitalWrite(pingPin, HIGH);
 delayMicroseconds(5);
 digitalWrite(pingPin, LOW);
 pinMode(pingPin, INPUT);
 duration = pulseIn(pingPin, HIGH);
 inches = microsecondsToInches(duration);
 cm = microsecondsToCentimeters(duration);  
 Serial.print(inches);
 Serial.print("in, ");
 Serial.print(cm);
 Serial.print("cm");
 Serial.println(); 
 delay(80);

} long microsecondsToInches(long microseconds) {

 return microseconds / 74 / 2;

} long microsecondsToCentimeters(long microseconds) {

 return microseconds / 29 / 2;

} </syntaxhighlight>