Getting Started with Seeed Studio XIAO-RS485-Expansion-Board

Hardware Overview

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Seeed Studio XIAO RS485-Expansion-Board	Seeed Studio XIAO ESP32-C3
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Pinout Diagram

XIAO RS485 Expansion indication diagram

• 5V OUT/IN SWITCH : One is the input and output of the 5V port, when the slave set the IN file, as the input, when the host set the OUT file, this port is discharged externally, can be connected to the sensor to the sensor power supply.

• 120R SWITCH : The 120R switch is used to determine whether the 120 ohm resistor is accessible or not. 485 needs to add a 120 ohm resistor at the beginning and end of long wiring environments to do the matching and ensure communication.

• INT : Reserved interrupt port.

tip

When it is used as an input mode, you need to turn the switch to IN, and if it is used as an output mode, you need to turn the switch to OUT to prevent burning out.

Connection Schematic

Two RS485 expansion board connections

Software Overview

Sender Code

#include <HardwareSerial.h>

HardwareSerial mySerial(1); 


#define enable_pin D2 // Define the enable pin as D2

void setup() {
  Serial.begin(115200); // Initialize the hardware serial with a baud rate of 115200
  mySerial.begin(115200, SERIAL_8N1, 7, 6); // RX=D4(GPIO4), TX=D5(GPIO5)

  
  // Wait for the hardware serial to be ready
  while(!mySerial);
  // Wait for the hardware serial to be ready
  while(!Serial);

  pinMode(enable_pin, OUTPUT); // Set the enable pin as an output
  digitalWrite(enable_pin, HIGH); // Set the enable pin to high
}

void loop() {
if (Serial.available()) {
    String receivedData = Serial.readStringUntil('\n'); // Read the data from the hardware serial until a newline character

    // If the received data is not empty
    if (receivedData.length() > 0) {
        Serial.println("Send successfully"); // Print a success message
        mySerial.print("Master send information is: "); // Send a prompt message to the hardware serial
        mySerial.println(receivedData); // Send the received data to the hardware serial
    }
  }
}

• HardwareSerial Library: Allows the creation of additional serial ports on ESP32, typically used for communication with devices (such as sensors or modules).

• HardwareSerial mySerial(1); : Defines a HardwareSerial object named mySerial, using D5 and D4 as the receive and transmit pins.

• #define enable_pin D2: Defines an enable pin used to control the sending and receiving state of the RS485 module.

• setup():

  • Serial.begin(115200: Initializes the hardware serial port with a baud rate of 115200.
  • mySerial.begin(115200, SERIAL_8N1, 7, 6);: RX=D4(GPIO4), TX=D5(GPIO5).
  • while(!mySerial): Waits until the hardware serial is ready for communication.
  • while(!Serial): Waits until the hardware serial is ready for communication.
  • pinMode(enable_pin, OUTPUT): Configures the enable_pin as an output pin to control the RS485 module.
  • digitalWrite(enable_pin, HIGH): Sets the enable_pin to HIGH, configuring the RS485 module for sending mode.

• loop():

  • if (receivedData.length() > 0): Checks if there is any data available to read from the hadware serial port.
  • String receivedData = Serial.readStringUntil('\n'); : Read the data from the hardware serial until a newline character
  • Serial.println("Send successfully"): Print a success message.
  • mySerial.print("Master send information is: "): Send a prompt message to the hardware serial.
  • mySerial.println(receivedData) :Send the data you need to an RS485 expansion board.

Receiver Code

#include <HardwareSerial.h>

HardwareSerial mySerial(1); // Use UART2
#define enable_pin D2 // Define the enable pin as D2

void setup() {
  Serial.begin(115200); // Initialize the hardware serial with a baud rate of 115200
  mySerial.begin(115200, SERIAL_8N1, 7, 6); // RX=D4(GPIO4), TX=D5(GPIO5)
  
  // Wait for the hardware serial to be ready
  while(!Serial);
  // Wait for the hardware serial to be ready
  while(!mySerial);
  
  pinMode(enable_pin, OUTPUT); // Set the enable pin as an output
  digitalWrite(enable_pin, LOW); // Set the enable pin to low
}

void loop() {
  // Check if there is data available from the hardware serial
  if (mySerial.available()) {
      String receivedData = mySerial.readStringUntil('\n'); // Read strings based on newlines
      Serial.print("Received data: ");
      Serial.println(receivedData); // Direct printing of received data
  }
}

• HardwareSerial Library: Allows the creation of additional serial ports on ESP32, typically used for communication with devices (such as sensors or modules).

• HardwareSerial mySerial(1);: Defines a HardwareSerial object named mySerial, using D5 as RX and D4 as TX.

• define enable_pin D2: Defines an enable pin used to control the sending and receiving state of the RS485 module.

• setup():

  • Serial.begin(115200: Initializes the hardware serial port with a baud rate of 115200.
  • mySerial.begin(115200, SERIAL_8N1, 7, 6);RX=D4(GPIO4), TX=D5(GPIO5).
  • while(!Serial): Waits until the hardware serial port is ready for communication.
  • while(!mySerial): Waits until the hardware serial port is ready for communication.
  • pinMode(enable_pin, OUTPUT): Configures the enable_pin as an output pin to control the RS485 module.
  • digitalWrite(enable_pin, LOW): Sets the enable_pin to low, configuring the RS485 module for receiving mode.

• loop():

  • if (mySerial.available()): Checks if there is any data available to read from the hadwareware serial port.
  • String receivedData = mySerial.readStringUntil('\n');: Read strings based on newlines
  • Serial.print("Received data: ");: Prints a message to the hardware serial indicating that data has been received.
  • Serial.println(receivedData);: Print the data sent to the receiver RS485.

RS485 Transmission Result

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