Proximity Switch for LED via IR

Thread Starter


Joined Aug 21, 2012
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 ( 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?



Joined Aug 7, 2008
Is '" the LED " going to be under the beer container, or in a ring around the container? What containers are allowed?


Joined Nov 30, 2010
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?