Sending a light beam through the liquid would be ok if the liquids weren't potentially opaque, like Bailey's Irish Cream. Also, the color of the liquid may give you problems. For instance, if you use a red LED and try to beam it through creme de menthe (which is oftentimes green) the red light could be optically filtered out.
JB
abt hyedenny's idea ==
well the idea would still work, we place the ir receiver to receive the signal from ir transmitter when the bottle is empty and to give a HIGH. Then we put the full bottle and ir is either blocked by the opaque liquid / refracted and does not reaching the receiver/ is weak because of coloration of liquid etc...in general will always be less than the signal that would be received if it is empty and a simple comparator circuit would do what we want. HOWEVER hyedenny the problem is that we would require to adjust the values everytime when we use different alcohol bottles. Because the bottles will also be colored/will have different thickness of glass etc.
Thinking about this now i think what i need to do is just place the ir transmitter and receiver at a small distance apart on a vertical bar that is originating for the bottle cap.
We set the comparator value by just find the value for air. (empty) and then put it in a liquid it will have some different value and once the bottle is empty the high could be noticed. the value of ir in air will be same for all the bottles as there is no glass /liquid/variable involved.
the only thing we would be looking for is any change at the receiving end. This just came to my mind as i was typing this post about how it is not possible.
Following up to this idea, i will go and search for ir transmitter and receiver. are they available premade and small and are they cheap ? hopefully ...will update if/when i find them.
possible concern, how big is the receiver and what about the power going into the receiver ...is/will it be safe to be having a receiver in liquid
thanx[/quote]