RS485 UV Sensor for Arduino- DFRobot

Introduction

The UV sensor uses a photoelectric detector to receive UV light wave electrical signals, and can measure the UV intensity and index values in the wavelength range of 290-390nm. The internal circuit uses imported industrial-grade microprocessor chips and high-precision UV sensors to ensure the excellent reliability and stability of the product.

The UV sensor uses the standard Modbus-RTU 485 communication protocol and DC5-30V wide voltage power supply. It can be used with the TTL to RS485 expansion board (DFR0259) or Gravity: Active Isolated RS485 to UART Signal Adapter Module (DFR0845) to read the UV intensity and index values on the Arduino UNO R3, quickly build a test environment, and the wiring method is simple and easy to use. The UV sensor has an IP67 protection level and is made of metal aluminum shell. It is widely used in environmental monitoring, health protection monitoring, crop growth monitoring, photovoltaic systems, laboratory research and other fields.

What is UV?

Ultraviolet (UV) is an invisible electromagnetic wave with a shorter wavelength than visible light but longer than X-rays. The wavelength of UV light usually ranges from 10 nanometers (nm) to 400 nanometers. UV light can be divided into three main types according to its wavelength: UVA, UVB and UVC.

Biological effects:

Role in nature:

Hazards of UV rays:

UV Index range and health recommendations

1. 0-2: Low risk

2. 3-5: Moderate risk

####3. 6-7: High Risk

####4. 8-10: Very High Risk

####5. 11+: Very High Risk

Features

Applications

Specifications:

Board Overview

Num Label Description
Brown line VCC Power input positive pole, DC5-30V power supply
Black line GND Power ground wire
Yellow line 485-A RS485 data line A
Blue line 485-B RS485 data line B

Dimensional Drawing

Dimensional Drawing

Communication Protocol

1. Basic communication parameters

Interface Encoding Data bits Parity bits Stop bits Error checking Baud rate
RS485 8-bit binary 8 None 1 CRC 2400bit/s, 4800bit/s, 9600 bit/s configurable, default 4800bit/s

2. Data frame format definition

Using Modbus-RTU communication protocol, the format is as follows:

Initial structure ≥4 bytes of time

Address code = 1 byte

Function code = 1 byte

Data area = N bytes

Error check = 16-bit CRC code

End structure ≥4 bytes of time

Address code: The address of the sensor, which is unique in the communication network (factory default 0x01).

Function code: The function indication of the command sent by the host. This sensor reads the register function code 0x03 and writes the register function code 0x06

Data area: The data area is the specific communication data. Note that the high byte of 16-bit data is in front!

CRC code: A two-byte check code.

Host inquiry frame structure:

Address code Function code Register start address Register length Check code low bit Check code high bit
1byte 1byte 2byte 2byte 1byte 1byte

Slave response frame structure:

Address code Function code Number of valid bytes Data area 1 Data area 2 Nth data area Check code
1byte 1byte 1byte 2byte 2byte 2byte 2byte

Register address

Register address Content Operation Range and definition
0000H UV intensity Read only 100 times the actual value
0001H UV index Read only Actual value
0052H UV intensity deviation Read and write 100 times the actual value
07D0H Device address Read and write 1~254 (factory default 1)
07D1H Device baud rate Read and write 0 represents 2400, 1 represents 4800, 2 represents 9600

3. Communication protocol example and explanation

3.1. Read the current UV intensity value

Inquiry frame:

Address code Function code Register start address Register length Check code low bit Check code high bit
0x01 0x03 0x00 0x00 0x00 0x01 0x84 0x0A

Response frame:

Address code Function code Return valid bytes UV intensity value Check code low bit Check code high bit
0x01 0x03 0x02 0x01 0x43 0xF8 0x25

Ultraviolet intensity value:

0143 (hexadecimal) = 323=> Ultraviolet intensity = 3.23mW/cm2

3.2, read the current UV index value

Inquiry frame:

Address code Function code Register address UV index value Check code low Check code high
0x01 0x03 0x00 0x01 0x00 0x01 0xD5 0xCA

Response frame:

Address code Function code Return valid bytes UV index value Check code low Check code high
0x01 0x03 0x02 0x00 0x03 0xF8 0x45

UV index:

0003 (hexadecimal) = 3 => UV index = 3

3.3 modify the current address

Inquiry frame: (modify the current address to 0x02)

Address code Function code Register address Modify value Check code low position Check code high position
0x01 0x06 0x07 0xD0 0x00 0x02 0x08 0x86

Response frame:

Address code Function code Register address Modify value Check code low position Check code high position
0x01 0x06 0x07 0xD0 0x00 0x02 0x08 0x86

3.4 Modify the current baud rate

Inquiry frame: (Modify the current baud rate to 9600)

Address code Function code Register address Modify value Check code low bit Check code high bit
0x01 0x06 0x07 0xD1 0x00 0x02 0x59 0x46

Response frame:

Address code Function code Register address Modify value Check code low bit Check code high
0x01 0x06 0x07 0xD1 0x00 0x02 0x59 0x46

3.5 Query current address and baud rate

Inquiry frame:

Address code Function code Register address Data length Check code low Check code high
0xFF 0x03 0x07 0xD0 0x00 0x02 0xD1 0x58

Response frame:

Address code Function code Return valid bytes Address Baud rate Checksum low bit Checksum high bit
0x01 0x03 0x04 0x00 0x01 0x00 0x01 0x6A 0x33

The real address of the device read is 01, and the baud rate is 0x01, that is, 4800.

Tutorial

Requirements

Connection Diagram

If the power of the RS485 device is small and the required current is less than 12V-160mA, the RS485 to UART signal conversion module does not require a 12V external power supply, making wiring more convenient.

Sample Code

#include <SoftwareSerial.h>
SoftwareSerial mySerial(2,3);
uint8_t Com[8] = { 0x01, 0x03, 0x00, 0x00, 0x00, 0x01, 0x84, 0x0A };
uint8_t Com1[8] = { 0x01, 0x03, 0x00, 0x01, 0x00, 0x01, 0xD5, 0xCA };
void setup() {
  Serial.begin(9600);
  mySerial.begin(4800);
}
void loop() {
  float UV = readUV();
  Serial.print("UV = ");
  Serial.print(UV);
  Serial.print(" mW/cm² ");
  uint16_t UVI = readUVI();
  Serial.print("UVI = ");
  Serial.println(UVI);
  delay(1000);
}

float readUV(void) {
  uint8_t Data[10] = { 0 };
  uint8_t ch = 0;
  float data;
  bool flag = 1;
  while (flag) {
    delay(100);
    mySerial.write(Com, 8);
    delay(10);
    if (readN(&ch, 1) == 1) {
      if (ch == 0x01) {
        Data[0] = ch;
        if (readN(&ch, 1) == 1) {
          if (ch == 0x03) {
            Data[1] = ch;
            if (readN(&ch, 1) == 1) {
              if (ch == 0x02) {
                Data[2] = ch;
                if (readN(&Data[3], 4) == 4) {
                  if (CRC16_2(Data, 5) == (Data[5] * 256 + Data[6])) {
                    data= (Data[3] * 256 + Data[4]) / 100.00;
                    flag = 0;
                  }
                }
              }
            }
          }
        }
      }
    }
    mySerial.flush();
  }
  return data;
}

int readUVI(void) {
  uint8_t Data1[10] = { 0 };
  int16_t data1;
  uint8_t ch1 = 0;
  bool flag1 = 1;
  while (flag1) {
    delay(100);
    mySerial.write(Com1, 8);
    delay(10);
    if (readN(&ch1, 1) == 1) {
      if (ch1 == 0x01) {
        Data1[0] = ch1;
        if (readN(&ch1, 1) == 1) {
          if (ch1 == 0x03) {
            Data1[1] = ch1;
            if (readN(&ch1, 1) == 1) {
              if (ch1 == 0x02) {
                Data1[2] = ch1;
                if (readN(&Data1[3], 4) == 4) {
                  if (CRC16_2(Data1, 5) == (Data1[5] * 256 + Data1[6])) {
                    data1 = Data1[3] * 256 + Data1[4];
                    flag1 = 0;
                  }
                }
              }
            }
          }
        }
      }
    }
    mySerial.flush();
  }
  return data1;
}

uint8_t readN(uint8_t *buf, size_t len) {
  size_t offset = 0, left = len;
  int16_t Tineout = 500;
  uint8_t *buffer = buf;
  long curr = millis();
  while (left) {
    if (mySerial.available()) {
      buffer[offset] = mySerial.read();
      offset++;
      left--;
    }
    if (millis() - curr > Tineout) {
      break;
    }
  }
  return offset;
}

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;
}

Expected Results

Print the collected UV intensity and index values, which cannot be collected by ordinary indoor light sources.

FAQ

Possible reasons for no output or output errors:

  1. The sensor is a precision device. Please do not disassemble it by yourself when using it to avoid damage to the product.
  2. If the reading value is 0, check whether there is a light source and whether the product protective cover is removed.
  3. The 485 bus is disconnected, or the A and B lines are connected in reverse.
  4. Check whether the power supply meets the marking.

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