Basically the arduino board when programmed will switch the digital outputs high. Which will send 5 volts through the resistor and light the led's. Which will activate the opto isolator which will connect the contacts on the remote control. which will send the comand to the remote control sockets And turn on or off the lights, heating or anything you want.
this circuit shown is for the first on and off switches. just repeat the circuit for the following channels
I programed the software so when I pressed (H) in the terminal the arduino board will send a 1 second pulse to my remote control and switch my heating on. when I press(h) the board will send a 1 second pulse my heating switches off. (S) for security on (s) for security off (G) garden lights on (g) garden lights off
and so on this can be changed to any button you want