Introduction to Digital Input

Today, we will be introduced to digital inputs and we will be working with push button switches and LEDs to create interactive programs which we will define and control ourselves. Push button switches are really simple components. When you press a button or flip a lever, they connect two contacts together so that electricity can flow through them.

The little tactile switches that are used in this lesson have four connections, which can be a little confusing.

Actually, there are only really two electrical connections. Inside the switch package, pins B and C are connected together, as are A and D.

Now let us quickly wire up our circuit. This is pretty straightforward

                                                                                                  (Source:Elegoo Starter Kit)

What we want to achieve is simple, pressing the left button will turn the LED on while pressing the right button will turn it off. Let us dive into the code, once again I won’t be sharing the code to be downloaded, you can look at the images however, understand and then proceed to write the code on your own. This greatly helps in familiarizing with the syntax of the code and writing codes.

The Arduino’s digital pins can read only two states: when there is voltage on an input pin, and when there’s not. This kind of input is normally called digital (or sometimes binary, for two-states). These states are commonly referred to as HIGH and LOW. HIGH is the same as saying “there’s voltage here!” and LOW means “there’s no voltage on this pin!”. When you turn an OUTPUT pin HIGH using a command called digitalWrite(), you’re turning it on. Measure the voltage between the pin and ground, you’ll get 5 volts. When you turn an OUTPUT pin LOW, you’re turning it off.

The Arduino’s digital pins can act as both inputs and outputs. In your code, you’ll configure them depending on what you want their function to be. When the pins are outputs, you can turn on components like LEDs. If you configure the pins as inputs, you can check if a switch is being pressed or not. Since pins 0 and 1 are used for communicating with the computer, it’s best to start with pin 2.

The explanation is thus;

The first part of the sketch defines three variables for the three pins that are to be used. The 'ledPin' is the output pin and 'buttonApin' will refer to the switch nearer the top of the breadboard and 'buttonBpin' to the other switch.

The 'setup' function defines the ledPin as being an OUTPUT as normal, but now we

have the two inputs to deal with. In this case, we use the set the pinMode to be

'INPUT_PULLUP' like this:

pinMode(buttonApin, INPUT_PULLUP);

pinMode(buttonBpin, INPUT_PULLUP);

The pin mode of INPUT_PULLUP means that the pin is to be used as an input, but that if nothing else is connected to the input, it should be 'pulled up' to HIGH. In other words, the default value for the input is HIGH, unless it is pulled LOW by the action of pressing the button.

This is why the switches are connected to GND. When a switch is pressed, it connects the input pin to GND, so that it is no longer HIGH.

Since the input is normally HIGH and only goes LOW when the button is pressed, the logic is a little upside down. We will handle this in the 'loop' function.

In the 'loop' function there are two 'if' statements. One for each button. Each does a 'digitalRead' on the appropriate input.

Remember that if the button is pressed, the corresponding input will be LOW, if button A is low, then a 'digitalWrite' on the ledPin turns it on.

Similarly, if button B is pressed, a LOW is written to the ledPin.

Now you have an idea how digital inputs work, digital inputs allows us to be interactive in our program or project by taking inputs from the user (you in this case) and then acting upon that input. Here we used a simple response such as turning on an LED but it could be more interesting such as telling a robot to pick up an item or perform another action like dancing. Ciao!