Example code for driving the Sainsmart 16-Channel 9-36V USB Relay Module (Product 101-70-208)

sainsmart_16_relay.py

#!/usr/bin/env python3

"""
Example code for driving the Sainsmart 16-Channel 9-36V USB Relay Module (Product 101-70-208)

Documents for this module were found at:
  https://s3.amazonaws.com/s3.image.smart/download/101-70-208/101-70-208.zip
        
The protocol appears to be MODBUS ASCII: 
  https://en.wikipedia.org/wiki/Modbus#Protocol_versions

This script depends on python serial library: 
  https://pythonhosted.org/pyserial/
"""

import serial
import time

def lrc(b):
    b = bytearray.fromhex(b)
    l = 0
    for i in b:
        l = (l+i)&0xff
    
    return ((l ^ 0xff) + 1) & 0xff

def cmd(relay, command):
    on = "FE0500{:02X}{:02X}00".format(relay, command)
    packet = ":{}{:02X}\r\n".format(on, lrc(on))
    return packet.encode('ascii')

def on_cmd(relay):
    return cmd(relay, 0xFF)

def off_cmd(relay):
    return cmd(relay, 0x00)

def all_on():
    return ":FE0F0000001002FFFFE3\r\n".encode('ascii')

def all_off():
    return ":FE0F00000010020000E1\r\n".encode('ascii')

def status():
    return ":FE0100000010F1\r\n".encode('ascii')

def main():
    ser = serial.Serial('/dev/ttyUSB0', 9600, timeout=1)  # open serial port

    print("Status")
    ser.write(status())
    print(ser.readline().hex())

    print("All On")
    ser.write(all_on())
    print(ser.readline().hex())
    time.sleep(1)

    print("All Off")
    ser.write(all_off())
    print(ser.readline().hex())
    time.sleep(1)

    for i in range(16):
        print("Turning on relay {}".format(i))
        ser.write(on_cmd(i))     # write a string
        time.sleep(.25)

    for i in range(16):
        print("Turning off relay {}".format(i))
        ser.write(off_cmd(i))
        time.sleep(.25)

    ser.close()             # close port

if __name__ == "__main__":
    main()