Arduio with light sensor

Hello,

I'm looking to make something that will detect if a cup is placed on a surface and if it is, it will make a ring of lights around the cup (for a beer poing table) and it would be able to keep track of the amount of cups on the table and what not...is this possible?

Take a look at rfid.

No that would take lots of RFID readers.

How about a small magnet on the underside of the cup and hall effect sensors or reed switches in the table.

Well... THAT was "entertaining"... I just spent 20 minutes looking in vain on the web for a decent description, or even photo, of something that I KNOW exists!

So instead, I'll just "paint" it in words...

Once upon an time!!! you could buy a simple little device. You can still make your own, if you don't track a supplier down. (Don't be fooled into buying anything more complicated than what you need)

It had an LED and a photosensor embedded in a small block of plastic. They both pointed the same way. When something was in front of one of these reflective opto sensors, the light from the LED bounced off the thing in front of it, back into the photosensor.

As they say at "CompareTheMeerkat.com"... Simples!

=== Regarding your countertop... if there were specific places to put glasses to get lit up rings of LEDs, cool. I would compare this to a stove top, where the "rings" are in fixed positions.

For a whole new level of cool, how about a matrix of sensors... one every 5mm, say (expensive, but what the heck)... and a matrix of LEDs. The LEDs lit up for a given ring would now not always be the same.... move the glass 5mm, and the ring moves 5mm. A given LED might be at the top of a ring one day, or the side of one another day.

Oh dear... that has set me thinging FURTHER....

For a counter-top, you can assume some convenient opportunities. It isn't going to move. It will be under a ceiling. So embed upward looking photo sensors in the countertop, and put some good lights on the ceiling over it.

OR.... a webcam on the ceiling, looking down on the counter. As your hand moves to pick up a glass, the hand's shadow would be lit up by the LEDs under it.....

I'd better stop.

Angled half-silvered mirror and camera with wide-angle lens, and a low-res capture device, like...an Arduino?

I just spent 20 minutes looking in vain on the web for a decent description, or even photo, of something that I KNOW exists!

Do you mean this:-

Or even this:-

what about a force sensitive resistor? you could know if the cup is full or empty :)

yeah these all seem like awesome ideas- I completely forgot about the photoresistor...I could def. do that, but like said before, they would have to be static rings for each cup...

Would it have to be only a certain amount I could do or could I make 20 rings that would communicate with the arduino? or each othe-r example the arduino knows how many cups are left...etc