Logic input using pull up resistor

In digital electronics, we often use input/output in term of logic 1 or logic 0. What is it in real world? in brief, logic 1 can simply means 5V and logic 0 means 0V. Thus, if we need to apply logic 1 to a system, it means we need to supply 5V to that particular system. This can be done by using pull up resistor as shown below:

  

So what value resistor should you choose?

The short and easy answer is that you may use a resistor value on the order of 10kOhm for the pull-up.

The value of the pull-up resistor needs to be chosen to satisfy two conditions:

1. When the button is pressed, the input pin is pulled low. The value of the resistor controls how much current you want to flow from VCC through the resistor R1, through the button, and then to ground.
2. When the button is not pressed, the input pin is pulled high. The value of the pull-up resistor controls the voltage on the input pin.

reference : http://www.sparkfun.com/