GPIO Inputs - Button LED Control

In the GPIO LED Control section, we looked at how to crate an output pin on the GPIO and turn it on (3.3v) and of (0v).
In this section we will look at how to create an input pin, that is a GPIO pin that looks for an input (which will be a voltage). When we talk about voltages, the Raspberry Pi only sees a voltage in terms of an on (3.3v) or off (0v). However, other voltages will fall in to either the on or off state, and roughly speaking, these are:

Off = 0v - 1.2v
On = 1.3v - 3.3v

Remember, the GPIO pins are 3.3v as they are logic devices, attach more than 3.3v and you might have to buy a new Raspberry Pi!