The DFRobot_RS485 Expansion HAT is a hardware add-on designed for Raspberry Pi, enabling RS485 communication. RS485 is a robust communication standard widely used in industrial environments for long-distance and noise-resistant data transmission. This HAT simplifies the integration of RS485 communication into Raspberry Pi projects, making it ideal for applications such as industrial automation, sensor networks, and building management systems.

• Industrial automation and control systems
• Long-distance sensor data acquisition
• Building management systems (e.g., HVAC, lighting control)
• Communication with RS485-compatible devices like PLCs, motor controllers, and sensors
• Modbus RTU communication for industrial protocols

The DFRobot_RS485 Expansion HAT is designed to provide reliable and efficient RS485 communication. Below are its key technical details:

• Manufacturer: DFRobot
• Part ID: RS485 module
• Communication Protocol: RS485
• Input Voltage: 3.3V or 5V (via Raspberry Pi GPIO)
• Baud Rate: Up to 115200 bps
• Operating Temperature: -40°C to 85°C
• Dimensions: 65mm x 56mm
• Connector Type: Terminal block for RS485 wiring
• Compatibility: Raspberry Pi 4B/3B+/3B/2B/Zero/Zero W

The RS485 Expansion HAT connects to the Raspberry Pi via the GPIO header. Below is the pin configuration:

The DFRobot_RS485 Expansion HAT is easy to set up and use with a Raspberry Pi. Follow the steps below to integrate it into your project:

1. Attach the HAT: Align the RS485 Expansion HAT with the Raspberry Pi GPIO header and press it down gently to ensure a secure connection.
2. Connect RS485 Wires: Use the terminal block on the HAT to connect the RS485 A(+) and B(-) lines to your RS485 network.
3. Power the Raspberry Pi: Ensure the Raspberry Pi is powered via its standard power supply.

1. Enable UART:
   • Open the Raspberry Pi configuration tool:

     sudo raspi-config
     

   • Navigate to Interfacing Options > Serial Port.
   • Disable the login shell over serial and enable the serial port hardware.
2. Install Required Libraries: Install Python libraries for serial communication:

   sudo apt update
   sudo apt install python3-serial
   

Below is an example Python script to send and receive data over RS485 using the HAT:

import serial
import time

ser = serial.Serial( port='/dev/ttyS0', # UART port baudrate=9600, # Baud rate parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS, timeout=1 # Timeout in seconds )

try: while True: # Send data over RS485 ser.write(b'Hello RS485!\n') # Send a message print("Message sent: Hello RS485!")

    # Wait for a response
    time.sleep(1)
    if ser.in_waiting > 0:  # Check if data is available
        response = ser.read(ser.in_waiting).decode('utf-8')
        print(f"Received: {response}")

except KeyboardInterrupt: print("Exiting program...") finally: ser.close() # Close the serial port

• Termination Resistor: If the RS485 network is long or has multiple devices, ensure proper termination resistors are used to prevent signal reflections.
• Baud Rate Matching: Ensure all devices on the RS485 network use the same baud rate.
• Grounding: Connect the GND of the RS485 HAT to the GND of the RS485 network for proper signal reference.
• Driver Enable Pin: The DE/RE pin is controlled automatically by the HAT, but ensure GPIO17 is not used for other purposes in your project.

1. No Data Transmission or Reception:

   • Verify the RS485 A(+) and B(-) lines are correctly connected.
   • Check the UART port configuration and ensure the correct port is used in the code.
   • Ensure the baud rate and other serial settings match across all devices.

2. Data Corruption:

   • Check for proper termination resistors at both ends of the RS485 network.
   • Ensure the cable length and quality are suitable for RS485 communication.

3. HAT Not Detected:

   • Ensure the HAT is securely connected to the Raspberry Pi GPIO header.
   • Verify that UART is enabled in the Raspberry Pi configuration.

Q: Can I use this HAT with other single-board computers?
A: The HAT is designed for Raspberry Pi GPIO headers. However, it may work with other boards that have compatible UART pins, but additional wiring and configuration may be required.

Q: What is the maximum communication distance for RS485?
A: RS485 supports communication distances of up to 1200 meters, depending on the cable quality and baud rate.

Q: Can I use this HAT for Modbus RTU communication?
A: Yes, the HAT supports Modbus RTU communication. You can use Python libraries like pymodbus to implement Modbus protocols.

Q: How do I identify the UART port on my Raspberry Pi?
A: On most Raspberry Pi models, the UART port is /dev/ttyS0 or /dev/serial0. Use the command ls /dev/serial* to list available serial ports.

By following this documentation, you can effectively integrate the DFRobot_RS485 Expansion HAT into your Raspberry Pi projects for reliable RS485 communication.