8 Channel RS485 MODBUS RTU relay board type R421A08

This Python project can control up to 64 individual 8 channel R421A08 relay boards from the command line and GUI. It uses a universal USB - RS485 dongle.

The following hardware is required for this project:

WARNING: DO NOT USE THIS RELAY BOARD WITH 230V AC!
The distance between relay traces on the PCB are < 2mm without holes for isolation. This is dangerous when using it with high voltages. See the picture above.

The 16 relay board version works by changing NUM_RELAYS = 16 in R421A08.py as reported by a user in issue #1 .

This project requires a RS485 - USB dongle which is widely available, for example:

getting_started.py

import time
import relay_boards
if __name__ == '__main__':
    print('Getting started R421A08 relay board\n')
    # Create MODBUS object
    _modbus = relay_modbus.Modbus(serial_port=SERIAL_PORT)
    # Open serial port
    try:
        _modbus.open()
    except relay_modbus.SerialOpenException as err:
        print(err)
        sys.exit(1)
    # Create relay board object
    board = relay_boards.R421A08(_modbus, address=1)
    print('Status all relays:')
    check(board.print_status_all())
    time.sleep(1)
    print('Turn relay 1 on')
    check(board.on(1))
    time.sleep(1)
    print('Turn relay 1 off')
    check(board.off(1))
    time.sleep(1)
    print('Toggle relay 8')
    check(board.toggle(8))
    time.sleep(1)
    print('Latch relays 6 on, all other relays off')
    check(board.latch(6))
    time.sleep(1)
    print('Turn relay 4 on for 5 seconds, all other relays off')
    check(board.delay(4, delay=5))
    time.sleep(6)
    print('Turn relays 3, 7 and 8 on')
    check(board.toggle_multi([3, 7, 8]))
    time.sleep(1)
    print('Turn all relays on')
    check(board.on_all())
    time.sleep(1)
    print('Turn all relays off')
    check(board.off_all())
    time.sleep(1)

Please refer to the Wiki page for installation and usage.

MODBUS Application Protocol Specification v1.1.b

The following Python packages are available in this project:

MODBUS is an open binary serial communication protocol, mainly used for PLCs.