i have posted a nice demo of an opto-coupler with a video and circuit diagrams. have a look at them on www.hardikpandya.com.
I wonder what I can learn from the video?
Also could you explain a little bit more: What kind of LED is is inside an optocoupler? Is it IR? How to connect it to the Arduinio for output? HOw to connect the transistor side to the Arduino (for input)?
What do you do with the B-connector?
What types are chaepest? Do they have drawbacks?
you can not learn. you can see the operation of an opto-coupler. its not a tutorial. maybe you did not notice it in the title. Its a demo. 
So you posted it for our amusement?
@rc: perhaps you find this place as your own little wonderland. if you dont find it worth looking, you should better look at your own blog with some "useful" information.
@the person with amusement comment: with all due respect, that was only to show the operation, not for amusement. Electronics is amusement only when you don't know the knowhow.
I can't believe I just spent 30 seconds watching a video of a blinking LED.
Just out of interest, what is the current through the visible LED?
Mr AWOL, the current through the output side of MCT2E is 50mA through the LED. Glad you asked.