Usage Example: Raspberry Pi RS-485 HAT Modbus Communication

Hardware Preparation

• Dual-channel RS485 Expansion Hat for Raspberry Pi (SKU:DFR0824)×1
• RS485 Laser Ranging Sensor (SKU:SEN0492)×1
• Raspberry Pi 4 Model B - 8GB (SKU:DFR0697)×1
• 5V Power Supply

Wiring Diagram

Download Routine

Run the two statements below in the Raspberry Pi terminal to download the routine to the Raspberry Pi desktop.

cd Desktop
git clone https://gitee.com/DFRobot/DFRobot_CH432T_raspberrypi

Enter the statement below in Raspberry Pi to find ch432t_demo.py and double click to open it. According to Modbus frame format, modify the program to make it suitable for the RS485 laser ranging sensor used here.

cd /home/pi/Desktop/DFRobot_CH432T_raspberrypi/examples/

Instructions for Change

1、

2、

3、

Change Program

The modified codes:

from __future__ import print_function
import sys
import os
sys.path.append(os.path.dirname(os.path.dirname(os.path.realpath(__file__))))

import time

import modbus_tk.defines as cst
from modbus_tk import modbus_rtu

from DFRobot_CH432T import *   # Import DFRobot_CH432T replace importing serial library

addr_sensor = 0x50                            
sensor_baudrate = 115200                    

PORT="CH432T_PORT_2"
ser = DFRobot_CH432T(port=PORT, baudrate=115200, bytesize=8, parity='N', stopbits=1)

def main():
  print("This is a demo of how to use a Modbus sensor.")
  print("If you want it to work, make sure you have connected your Modbus device and changed the relevant parameters in the demo to those of your device!\r\n")

  master = modbus_rtu.RtuMaster(ser)
  master.set_timeout(5.0)
  master.set_verbose(True)
  print("ser.name = ", ser.name)

  try:
    while True:
      ser.baudrate = sensor_baudrate   
      data = master.execute(addr_sensor, cst.READ_HOLDING_REGISTERS, 0x34, 1)
      distance = data[0]/10   
      print("distance = ", distance)
      time.sleep(3)

      #ser.baudrate = relay_baudrate  

  except Exception as err:
    print(str(err))


if __name__ == "__main__":
  main()

Save and exit after completing changing, and enter the command below to enter the config interface.

sudo raspi-config

Select Interface Options -> Serial Port -> SPI to enable the SPI interface

Then reboot Raspberry Pi

sudo reboot

Enter the statement below in Raspberry Pi to find ch432t_demo.py.

cd /home/pi/Desktop/DFRobot_CH432T_raspberrypi/examples/

Enter the statement below to run the program and get data.

python ch432t_demo.py

The result is as shown in the figure below:

The distance read by the RS485 laser ranging sensor can be printed out, which means the RS485 communication is successful.