This is a series of switches that I made to detect and count drops of liquid as they fill some vessel, in this case a shot glass, and to detect and signal that the vessel is full. Two wires, one connected to ground and another connected to 5 volts of power, were positioned over the opening of the glass about a millimeter apart. When water (with some salt in it) dripped from an inverted container above the glass, the drop of water closed the circuit between the two wires for a brief period of time which, had all gone according to plan, my arduino would have counted. Two more wires, also connected to ground and a separate 5 volt power supply, were positioned just below the inner rim of the shot glass. When the glass was filled, this circuit was closed, and a red LED blinked rapidly to signal that this was the case. Some programming kept me from counting the drops correctly, so I just made it blink every time a drop fell into the glass.