Hi, I'm trying to build a very simple (and cost effective) circuit that when you place a cup of beer down it lights up the LED and when you take it off the LED goes off. For a Beer Pong table I've built.

I've found a few schematics online that use phototransistors but since I need 20 of these circuits its simply too expensive to buy 20 phototransistors (plus all the other stuff for those schematics).

I have stumbled across one simple circuit that uses an IR LED as a receiver with an op amp (http://www.artemlive.com/cgi-bin/news?c=v&id=758) but the website doesn't give the full schematic and the image of the breadboard is pretty confusing.

I only have a vague knowledge of op amps myself, but would I be correct in saying the circuit schematic below would work and in the probable case that I've made a glaring error what could I do to rectify it?

 

Is '" the LED " going to be under the beer container, or in a ring around the container? What containers are allowed?

 

Along the same idea, does beer reflect IR?
Does the cup reflect IR?
There is just so much information I don't have. I've rarely said this but, could you ramble on a while? Do you have ideas about flush mounting the sender and receiver? Cutting a shallow divot in the surface so the beer cups will be properly located?

ps, that battery symbol in your drawing seems wrong. Is it trying to be a ground symbol?