Here is the final assembled Remote flash trigger using opto-isolator , please be warned the final packaging is hardly the epitome of finesse.
View of the internals
close-up of the circuit (notice it just 2 resistors, 1 transistor and one IC on the board + a 02 connectors. Rest of the stuff in inside the Red cover on top
The final product, very simple and very basic, but it gets the job done.