Lesson 5 · Build And Program A Button Circuit

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Suggested Time: 60-75 minutes

Lesson Plan

What You’ll Need

Before we get started, let’s make sure that we have all the parts.

• 1 x Arduino Uno Compatible Board
• 1 x 10 kOhm Resistor
• 1 x 470 Ohm Resistor
• 1 x 4-pin Button
• 1 x USB Cable
• 1 x Computer

Getting To Know Your Robot’s Brain

Just like the human brain, your robot’s brain has hundreds of wire pathways that are connected together to help your robot store information and make decisions. Each of these wire pathways in your robot is a circuit. As we learned in the previous lesson, a circuit is just another way of describing a pathway for electricity to flow. Your robot’s brain is called the Arduino Uno. In this lesson, you’ll not only be connecting your LED and button to your brain, but you’ll be learning how to control the LED through code!

Connecting Your Brain To Your Computer

Plug your Arduino Uno into your computer using the USB cable. The red light on your Uno

Connecting Your LED And Button To Your Brain

Next, we need to connect the LED and button to the Arduino Uno. Previously, the LED would turn on and off without any code. This time we want to connect it in a way so that the button sends a signal to the Arduino Uno, and then the Arduino Uno processes code to turn the LED on or off. In order to do this we need to connect the LED and button to a special place, called a pin.

A pin on the Arduino Uno is a power source that can be turned off and on depending on its computer code.

Build The Button Circuit

Study the circuit below. Notice that the button is connected to pin 2 and the LED is connected to pin 7.

Go ahead and remove everything from your breadboard and wire the circuit based on the diagram below. A few things to note:

• Use a red wire for the 5V connection
• Use a black wire for the GND connection
• A second black wire connected two rows together, causing both rows to become connected to GND.
• A 470 Ohm resistor (yellow, purple, brown, gold) is connected to the LED
• A 10 kOhm resistor (brown, black, orange, gold) is connected to the button
• Use yellow wires for the pin connections

Introduction To Coding

It’s now time to start coding. To do this, we first need to create instructions to send to your robot’s brain to tell it to turn the LED on. The process of creating instructions for your robot is called computer programming or software engineering. The actual set of instructions that we create is called computer code.

What is Computer Code?

Let’s go back to our human brain analogy. A human brain without any information stored in it wouldn’t be able to accomplish any of the functions that we do every day (e.g. walking, running and talking). Likewise, a computer needs to have information in it to make a robot function. As humans, we learn instructions so that we can accomplish tasks like washing our hands or making a sandwich. We learn these tasks by reading, listening or observation. Computers learn by receiving computer code, written by humans.

How Computer Code Works

These instructions will be followed by the computer in the order that they are written. When the computer gets to the end of the list of instructions, it goes back to the beginning of the list of instructions and starts over.

Sending Computer Code to the Uno

After you’ve created your computer code, you’ll need to send the code to the Uno

Open Your IDE

It’s time to start coding! Go ahead and open your IDE

If you need a refresher on the IDE, go to: Setting Up Your Computer.

void setup() {
    //- the code in here runs one time upon power up
}

void loop() {
    //- after the setup code runs once, the code in here runs forever in a loop
}

Programming the Button

Conditional Logic

In programming, conditional logic is used to decide a course of action depending on a condition. Conditional logic is something we use in our everyday life without even recognizing it. Examples are:

• If I’m hungry, I eat. Else, I don’t eat.
• If I’m cold, I wear a jacket. Else, I don’t wear a jacket.

You likely make hundreds of conditional logic decisions a day. Your robot can be programmed to make decision in this same fashion. The condition that we will program in the lesson is:

• If the button is pressed, then turn the LED on, Else, turn the LED off

See below for what if/else code looks like:

if ( ) {
    //- do something
}
else {
    //- do something else
}

Practice

Now that we know the basics of conditional logic, let’s write a program that turns ON the light if we press the button and turns OFF the light if we let go of the button. A few notes:

void setup()
{
  pinMode( 2 , INPUT);
  pinMode( 7 , OUTPUT);

}

void loop()
{
  if (digitalRead(2) == HIGH) {
    digitalWrite(7,LOW);
  }
  else {
    digitalWrite(7,HIGH);
  }
}

Our First Upload

We are now ready to upload our code to our robot. Before doing so, let’s check a few things.

• Confirm power. Make sure that the USB cable is connecting your Uno to your computer. A red light on your Uno should be on.
• Set your Board and Port.
• Click upload.

If you need detailed instruction on how to upload, revisit: Setting Up Your Computer.

After you successfully upload, try out your code to see if it works!

Challenges

Now that you know how to program a button, try the following challenges:

1. Modify your program so that it turns OFF when you press the button and ON when you let go.

2. Modify your program so that it blinks when you press the button and just stays OFF when you let go.

Additional Resources