Now I'll show you a very easy way how to control RS232 8 relays
with the help of Raspberry PI
Needed
1 RaspberryPI
1 RS232 KMTronic 8 Relay Board
1 USB cable
1 FTDI KMTronic
1 RS232 to TTL converter with MAX232
2 DB9 RS232 Male
12-volt power
recommend install Raspbian
DB9 RS232 Male to Male
FTDI to RS232 to TTL converter with MAX232
Sets baud rate of the USB relay
stty -F /dev/ttyUSB0 9600
How to switch on or off the relays
Shell code
#!/bin/bash
# sends on signal to the USB relay
echo -e "\xFF\x01\x01" > /dev/ttyUSB0 -----> ON
echo -e "\xFF\x01\x00" > /dev/ttyUSB0 -----> OFF