How to hook up photocoupler

[RicF]

I have a Silonex NSL-32 that I plan to use in a Tremulus Lune projet. I'm not sure how to hook the thing up. There's two long wires, and two thinner short wires, and on side has a dot. I could guess but can anyone clarify for me?

[petemoore]

An opto coupler has an LED and an LDR
 to find and establish the cathode of the diode [LED} use the DMM Diode checker [also continuity checker] you should see a number close to an LED"s foreward threshold when connecting two or the PC wires to the Diode checker...you'll have to swap the wires around, because inverting them...take an LED and see what the numbers look like on your DMM, when anode is + and Anode is -, then find similar 'numbers on your photocell, you should be able to determine which lead is - on the LED.
 The other two wires have the be the LDR, which, like a two leg resistor, has no polarity to it.