put your finger on it

Digital Input

First and foremost, it is important to know that there are only two possible states for a digital input: either ON or OFF. A switch, such as a push button is the simplest and most common example of digital transducer.

Digital Input is information represented solely in discrete form, using two states- 0 & 1, which we can describe in a circuit as ON & OFF. One of the great advantages of digital electronics is that we can design logic circuits delivering digital logic based on the NOT, AND and OR operations.

Pull-Down or Pull-Up resistor

When a button is pushed, and the circuit is closed, an ON signal is sent to the microcontroller via the digital input pin (in general a +5V signal). In this design, the OFF signal is 0V and the ON signal is +5V. However, if the button is not pushed, then the circuit is left open, any stray voltage can affect the input pin (e.g. radio waves, statics...). To avoid this, a very effective and simple solution is to ground the pin via a resitor of around R10K. Symmetrically, if your circuit is designed so that the OFF signal is +5V and the ON signal is 0V, then you will need a pull-up resitor (approx. R10K) that connects the pin to the +5V source.