I wonder how can I make the logic gate read 0V when it is open? For instance, the AND logic gate. If one of its input pin has 5V supply, and the other don't have, the output signal given to me is 5V. How can I make it 0V? Well, theoretically, it should be 0V, but in reality, it appears that it is 5V. Same goes with OR logic gate. If one of the inputs is 0V, and the other is not connected with any supply (not grounded - the wire is hanging), it gives an output value of 5V. We need this for our project. We have our own long equation (it involves 16 variables, ANDed to make it simplier - 8 inputs). We will be using this as a contact sensor. A insulator will be placed in between two conductors. One of the conductors will be connected with the 5V supply, and the other one will be to the logic gate input itself. If the two conductors does not make contact, the output remains high (5V).