Laser Ranging Distance Sensor RS485 4cm-4m Wiki - DFRobot

Introduction

This laser range sensor can be used to detect objects in 4~400cm with ±2cm accuracy. With 3 measurement modes supported, it is well applicable to various detection scenarios like security gate detection, access control systems, security alarm devices, smart trash cans, smart cars or robots for obstacle avoidance.
The sensor metal black shell adopts a threaded barrel design and its probe comes with an optical cover. The integrated design makes the product able to effectively filter optical interference, waterproof and shockproof. The sensor uses invisible laser and there is a voltage regulator circuit inside the module. It operates at 5V-36V and employs industrial 485 chip, which supports Modbus-RTU protocol and works well with industrial 485 devices. The sensor has an alarm output line that will be triggered to output Low steadily when the measurement distance is smaller than the user-set threshold.

Note: The data will be unstable when measuring black objects.

Specification

• Power Supply Voltage: 5-36 V
• Measuring Distance: 4-400 cm
• Measurement Accuracy: ±2 cm
• Launch Angle: 39.6°
• Receiving Angle: 36.5°
• Working Current: <38mA
• Communication Interface: RS485
• Communication Protocol: Modbus-RTU
• Waterproof Rating: IP67
• Baud Rate: 2400-921600 optional 115200 (default)
• Frequency: 20Hz (default)
• Working Temperature: -20~70°C
• Size: 21.5x21x8 mm / 0.85×0.83×0.31 inch

Dimension Figure

Board Overview

Communication protocol

The sensor adopts the industry standard Modbus protocol, the specific read and write format is as follows: Modbus communication, the command number is divided into two types, read command and write command, 0x03 (read command) reads the corresponding register data, 0x06 (write command) write data to the corresponding register.

Host sending frame (HEX)

The module address is 0x50 (default), the read command is 0x03, the register 0x34 (measurement distance), and the length is one bit. Command: 50 03 00 34 00 01 C8 45 Slave response frame (HEX)

The module address is 0x50, the read command is 0x03, and the length is 2 bits. Example: Read the measured distance Send command: 50 03 00 34 00 01 c8 45 Receive data: 50 03 02 07 0B 06 7F

Data analysis: 0x50 is Modbus address, 0x03 read command, 0x02 data length, 0x07 0x0B measurement data corresponding to 0x070B is decimal 1803, measurement distance is 1803mm, 0x06 0x7F is CRC check bit.

Register table

Tutorial for Raspberry Pi

Requirements

• Hardware
  • Raspberry Pi x 1
  • 6-in-1 multi-function to serial port module or USB to RS485 module x1
  • Laser ranging sensor RS485 (4m) x1

1. Connection Diagram

2. Check usb device

Type in the terminal

sudo ls -l /dev

Find the USB device that has just been connected to the Raspberry Pi (every time the USB device is connected to the Raspberry Pi, the device port will change, so you need to check the actual port each time when you connect to the Raspberry Pi)

3. Install the wiringpi library

cd /tmp

wget https://project-downloads.drogon.net/wiringpi-latest.deb //Download wiringpi library

sudo dpkg -i wiringpi-latest.deb //Install wiringpi library

4. Compile and run the sample code

Create a new folder on the desktop, create a new LaserRanging.c file in the folder, copy the code in and save it, then use the terminal to open the folder where the program is located, compile and run

gcc -Wall -lwiringPi -o LaserRanging LaserRanging.c

Then you can see the accurate measured distance value

Sample Code

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#include <wiringPi.h>

#include <wiringSerial.h>

int recData(unsigned char* buf);
unsigned int CRC16_2(unsigned char *buf, int len);

int fd;

unsigned char Data[8] = {0};

int main()
{
    if ((fd = serialOpen("/dev/ttyUSB0", 115200)) < 0) {     //You can change usb device port in line with the actual conditions here.
        fprintf(stderr, "Unable to open serial device: %s\n", strerror(errno));
        return 0;
    }
    while(1){
        delay(100);
        printf("%d mm\n",recData(Data));
    }
    return 1;

}

int recData(unsigned char* buf)
{
    char ret = 0;
    int jl=0;
    long curr = millis();
    char ch = 0;
    unsigned char COM[8]={0x50, 0x03, 0x00, 0x34, 0x00, 0x01, 0xC8, 0x45};
    write(fd, COM, 8);
    while(!ret){
        if (millis() - curr > 1000){
            //write(fd, COM, 8);
            curr = millis();
            printf("OK\n");
        }

        if(serialDataAvail(fd) > 0){
            delay(10);
            if (read(fd, &ch, 1) == 1){
                if(ch == 0x50){
                    buf[0] = ch;
                    if (read(fd, &ch, 1) == 1){
                        if(ch == 0x03){
                            buf[1] = ch;
                            if (read(fd, &ch, 1) == 1){
                                if(ch == 0x02){
                                    buf[2] = ch;
                                    if (read(fd, &buf[3], 4) == 4){
                                        // for(int i=0; i<7; i++){
                                        //     if(buf[i] < 0x10){
                                        //         printf("0");
                                        //     }
                                        //     printf("%x ", buf[i]);
                                        // }
                                        // printf("\n");
                                        // printf("%x\n", CRC16_2(buf, 5));
                                        // printf("%x\n", buf[5]*256+buf[6]); //Used to view the raw data of the distance measured by the sensor.
                                        if(CRC16_2(buf, 5) == (buf[5] * 256 + buf[6])){
                                            jl = buf[3]*256+buf[4];
                                            ret = 1;
                                        }

                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    return jl;
}

unsigned int CRC16_2(unsigned char *buf, int len)
{
  unsigned int crc = 0xFFFF;
  for (int pos = 0; pos < len; pos++)
  {
    crc ^= (unsigned int)buf[pos];
    for (int i = 8; i != 0; i--)
    {
      if ((crc & 0x0001) != 0)
      {
        crc >>= 1;
        crc ^= 0xA001;
      }
      else 
      {
        crc >>= 1; 
      }
    }
  }

  crc = ((crc & 0x00ff) << 8) | ((crc & 0xff00) >> 8);
  return crc;
}

FAQ

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