Generally, when we think about digital input and voltages for a 3.3-volt device such as the Raspberry Pi, we think of connecting a pin to the ground (0 volts) to drive it low or connect it to 3.3 volts to make it high. In most applications, this is exactly what we will strive to do. However, in truth, there is more to this story because GPIO pins don't just operate at two discrete voltage levels. Instead, they work within a range of voltages that define an input pin as being high and low. This applies to the Raspberry Pi and similar computers with GPIOs, microcontrollers, ICs, and breakout boards.
Consider the following diagram, which shows a voltage continuum between 0 and 3.3 volts, as well as three highlighted areas labeled low, floating, and high:
This illustration is telling us that if we apply a voltage between 2.0 volts and 3.3 volts, then the input pin will read as a digital high. Alternatively...
