# HC-SR04 Ultrasonic Module User Guide

Last week,  we really released many user guides and video tutorials, including Bluetooth Bee, Bluetooth Modem, NFC shield/module, and we do not know whether they are beneficial for your operation or not. If you have any advice or idea for our tutorial or technical support, please feel free to contact us. This time, we launched the HC-SR04 Ultrasonic Module User Guide, and our  technician also wrote  HC-SR04 demo for the widespread DIY hobbyists to download. Take a look.

## Part 1 Ultrasonic Introduction

The human ear can hear sound frequency around 20HZ ~ 20KHZ, and ultrasonic is the sound wave beyond the human ability of 20KHZ . The principle of ultrasonic distance measurement used the already-known air spreading velocity, measuring the time from launch to reflection when it encountered obstacle, and then calculate the distance between the transmitter and the obstacle according to the time and the velocity. Thus, the principle of ultrasonic distance measurement is the same with radar. Distance Measurement formula is expressed as: L = C X T In the formula, L is the measured distance, and C is the ultrasonic spreading velocity in air, also, T represents time (T is half the time value from transmitting to receiving ).

Application:

• Ultrasonic measurement of distance, depth and thickness;
• Ultrasonic testing;
• Ultrasound imaging;
• Ultrasonic machining, such as polishing, drilling;
• Ultrasonic cleaning;
• Ultrasonic welding;

## Part  2 HC-SR04  Introduction

Module Operating Principle

Set low the Trig and Echo port when the module initializes , firstly, transmit at least 10us high level pulse to the Trig pin (module automatically sends eight 40K square wave), and then wait to capture the rising edge output by echo port, at the same time, open the timer to start timing. Next, once again capture the falling edge output by echo port, at the same time, read the time of the counter, which is the ultrasonic running time in the air. According to the formular: test distance = (high level time * ultrasonic spreading  velocity in air) / 2, you can calculate the distance to the obstacle.

Feature:

• Stable performance
• Accurate distance measurement
• High-density
• Small blind

Application Area:

• Robotics barrier
• Object distance measurement
• Level detection
• Public security
• Parking detection

## Part 3 Use Freaduino UNO to test HC-SR04

Connection Description：D2<------>Trig D3<------>Echo (The users can define the connection pin by themselves)

Note：You need to set the Freaduino UNO switch in 5V Side when use together with HC-SR04 Module.

1. HCSR04 library function description Long timing()

Function name: timing Parameters: None Return Value: the time of ultrasonic from the transmitter to the receiver

float CalcDistance(long microsec,int metric)

Function name：CalcDistance

• microsec: the time of ultrasonic from the transmitter to the receiver
• metric: Set the unit of the return value ( the value of 1 for cm, and the value of 0 for in )

Return Value: the measured distance