How do pop dispensers always know when the cup is full?

Question

Pop dispensers always know when to stop pouring out pop into a cup no matter what size it is. It is not programmed to cup sizes, and it isn't a special button. You just put any cup there, and when it's full the pop stops. How does the machine do that?

Answer 1

It has a sensor!!!! or some of them are programed to fill that amount.

Answer 2

The machine looks for the hight of the cup by photo electric cells

Infra red light is send out and reflects on the cup, or not, and so measuring the high of the cup and how much to dispense. And if no cup no spilling.

Frank  

Answer 3

Actually, those dispensers are physic. They are from other little planets that come to our world to mess with us.

But I think the real answer is sensors. But how do they make them?

Answer 4

the machines usually dispense a certain amount, or i have seen ones that the weight of the cup triggers it to dispense a certain amount

Answer 5

They have sensors in them.