Arduino Hardware

An Arduino board is made up of a number of components, including a microcontroller, digital and analog pins, power pins, resistors, a diode, a capacitor, and an LED. Figure 1-1 shows an Arduino Uno .

A Microcontroller has a central processing unit (CPU); it stores the uploaded sketch and processes and directs the commands.

The digital and analog pins are used for sending and receiving digital and analog data.

The Arduino also has a serial interface that allows the Arduino to send data to a computer via the serial port; this is the way we will be sending data to and from a computer in this book.

Ohms Law

The physicist and mathematician Georg Simon Ohm discovered a relationship between voltage, current, and resistance; this relationship is called Ohms law. Ohms law says that voltage is equal to amps multiplied by resistance, and it is written as V = I * R where V is volts, I is current, and R is resistance. With this formula you can also find resistance R = V / I and to find current I = V / R, these can be seen in Figure 1-3.

The components on a circuit use part of the energy in the circuit and turn it into another form of energy such as light or sound. All the energy on a circuit needs to be used by the circuit. If all the energy isn’t used up it needs to go somewhere, or this can cause it to overheat or catch fire. For example, if there is an LED on circuit and it receives too much energy, the light will be very bright and it can blow out. With Ohms law you can calculate the resistance, instead of V = I * R you can find resistance using R = V / I, resistance equals voltage divided by current.

Resistors

Resistors are a crucial component for circuits as they limit the amount of current on the circuit. A resistor has a certain amount of resistance to the current flow. Every component has a maximum amount of current, measured in amps that it can safely use. For example, if a component can take a maximum of 0.023 amps, which is 23 milliamps, and your circuit is receiving 5V (volts), then a 220-ohm resistor will need to be added to the circuit to use the LED safely. The electrical components will use some of the power from the circuit; this is called a voltage drop so this can be taken into account when working out resistance. Figure 1-4 shows an example of how this is worked out with Ohms law, with different voltages and current.

When you get a component, it should also have a data sheet, which may be online. This will give you information about the voltage drop and the maximum amps. This will allow you to work out what resistor you need for your circuit.

Resistors have a value measured in ohms; they have a color code to show that value. The value of the resistor tells you what amount of current it will dissipate.

Electronic Circuit Diagrams

Circuit diagrams visually describe a circuit. There are sets of icons that are used for showing components on electronic circuits. In this book I won’t be using electronic circuit diagrams to show the circuits used in the projects but will use images of the Arduino and the components. Figure 1-5 gives you an idea of what a circuit diagram looks like. It is the circuit diagram for an LED.

Figure 1-6 shows some of the icons that can be used in a circuit diagram.

Downloading and Setting Up the Arduino IDE

When you open the IDE a new sketch should open. Figure 1-7 is an example of an edit window.

The sketch will contain two functions, setup and loop. There is a tick icon at the top of the page. This is pressed to verify that your code is written correctly. If there are any problems you will get a message in the console in red. The arrow icon is clicked when you want to upload the sketch to your Arduino. The console will show you messages connected to your sketch. It will show you any errors in your code and information when the sketch is verified and uploaded.

Connecting an Arduino to a Computer

You will need a USB 2.0 type B cable to connect an Arduino Uno to your computer. The USB will be used to send data to and from the Arduino as well as powering it. Different types of Arduinos will use different types of cable.

Once you’ve opened the IDE by double-clicking on the icon and connected the Arduino to your computer with the USB, you need to check the tools menu to see that the Arduino Uno is listed as the board and which port it is attached to. In the menu go to Tools/Board, and check that the board says “Arduino/Genuino Uno”; if it doesn’t, pick the Uno from the drop-down menu.

The Breadboard

The breadboard is used in electronics for prototyping; it is a way to attach components to an Arduino without soldering. It is made of plastic and has a series of holes in it for the pins of the components and for wires. They commonly have two strips of holes down either side for power and ground. Inside the breadboard are strips of metal that are conductive. The wires and pins connect with these strips of metal to make a circuit. They can come in different sizes. Figure 1-8 shows a breadboard.

Cables

The Arduino starter kit comes with a number of cables you can use in most of the projects to make a circuit between the Arduino and components using a breadboard. There are some components that have pins that are hard to fit into a breadboard. In Chapter 10 when you make a game controller, you may need to use cables with a different head. There three types of cables: male to male, female to male, and female to female. They are shown in Figure 1-9.

Analog Output

Analog output and input produce a range of numbers that go up and down in sequence. On an Arduino some of the digital pins have a “~” symbol next to them. These pins are used for analog output and use PWM (pulse width modulation).

Pulse Width Modulation

PWM is used to simulate an analog output with digital pins. A digital signal can be on or off, and it sends a pulse for on. PWM simulates an analog system using the digital signal by changing the length of the pulse; it’s “on” time to simulate pulses between 5V and 0V. Figure 1-12 shows the pulse width to simulate different voltages.

Analog Output

As the analog signal can produce a range of numbers, you can do things gradually. In this exercise an LED will fade up slowly before turning off then fading up again. The components for this exercise are the same as Figure 1-10. Make sure the Arduino is unplugged, and then set up the components as shown in Figure 1-13. The LED is connected to digital pin 9, which has a ~ next to it.

Create a new ino sketch, I called mine chapter_01_1.ino, and copy the code from Listing 1-2 into it.

int analogOutPin = 9;

int outputValue = 0;

void setup() {

  pinMode(analogOutPin, OUTPUT);

}

void loop() {

  if (outputValue >= 40){

     outputValue = 0;

  } else {

     outputValue = outputValue + 1;

  }

  analogWrite(analogOutPin, outputValue);

  delay(200);

}

Listing 1-2

chapter_01_1.ino

The Code Explained

To get the LED to fade up, you need to give it a value that increases in each loop. There are a number of new programming concepts in this code. Don’t worry too much if you don’t understand them all yet, as the next few chapters go into programming in more detail. Table 1-2 explains the code in chapter_01_1.ino in more detail.

Table 1-2

chapter_01_1.ino explained

int analogOutPin = 9;	Pin 9 will be used for the LED; it is common practice to store this number in a variable that is used throughout the program. This makes it easier to see what the number represents throughout the program and also allows you to change the pin number once in the code if you decide to use a different pin number.
int outputValue = 0;	A variable holds the value for the LED.
if (outputValue >= 40){        outputValue = 0; } else {        outputValue = outputValue + 1; }	An if else statement checks if something is true; if it is it does one thing and if not it does another. In this case it checks if the value of the variable outPutValue is greater or equal to 40; if it is it makes the variable contain the value 0, which turns the LED off, and if not it increases it by 1, turning the brightness on the LED up.
analogWrite(analogOutPin, outputValue );	The analogWrite function has two arguments: the pin number and a value, and in this case the value in outputValue is sent to the component attached to pin 9. In this case it is an LED, and this will change the brightness of the LED.

Upload the sketch to the Arduino; you should see the LED increase in brightness then go off.

Digital Input

A good circuit to show a digital input is a switch button. The switch button is either up or down, and it is in one of two states, pressed or not pressed. It brings in another concept called Input Pullup.

There is a problem for an Arduino with a switch. When a switch is open, it does not complete a circuit, and there is no voltage so the Arduino doesn’t know what the input is; it could be 0 or it could be 1. As it doesn’t know you can get strange results, it creates noise as the input value is unknown and it tries to put something in. This problem is solved with pullup resistors; it sets a voltage when the switch is open.

Pullup resistors are built into the Arduino and can be accessed when using the pinMode() function by setting it to INPUT_PULLUP instead of just INPUT. The pin will read HIGH when the switch is open and LOW when it is pressed.

Digital Input

For this exercise, you will use a button to switch on and off the LED on the Arduino. For it you will need:

• 1 x Arduino Uno

• 1 x switch button

Remember to disconnect the Arduino from your computer when you are changing components. The switch is attached to the breadboard. One pin is attached to ground the other to digital pin 2. Figure 1-14 shows the components needed and Figure 1-15 shows the setup of the Arduino.

Create a new sketch in the Arduino IDE, I called mine chapter_01_2, and copy in the code from Listing 1-3. Verify and upload the code to the Arduino. When you press the button the LED on the Arduino should light.

int buttonInput = 2;

int LEDOutput = 13;

void setup() {

pinMode(buttonInput, INPUT_PULLUP);

  pinMode(LEDOutput, OUTPUT);

}

void loop() {

  int sensorVal = digitalRead(buttonInput);

  if (sensorVal == HIGH) {

     digitalWrite(13, LOW);

  } else {

     digitalWrite(13, HIGH);

  }

}

Listing 1-3

chapter_01_2.ino

The Code ExplainedTable 1-3 explains the code for chapter_01_2.ino in more detail.

Table 1-3

chapter_01_2.ino explained

pinMode(buttonInput, INPUT_PULLUP);	You need to use INPUT_PULLUP as the second argument in the pinMode() function for the button switch.
int sensorVal = digitalRead(buttonInput);	The value of the switch is read into a variable on each loop.
if (sensorVal == HIGH) {       digitalWrite(LEDOutput, LOW); } else {       digitalWrite(LEDOutput, HIGH); }	An if/else statement checks if the switch is HIGH or LOW. Using the pullup means that the button’s logic is reversed. If it’s HIGH it means it’s up and so the LED is off. When it is LOW it is being pressed, which switched the LED on.

Analog Input

Analog input is used with components such as photoresitors and potentiometers, components that give varying values. An Arduino Uno can register values between 0 and 5 volts; with this you can get an analog input value between 0 and 1023. An analog input sends a signal voltage. When the signal voltage is received it is checked against an internal reference. An example is illustrated in Figure 1-16.

When a signal voltage is received it is tested against the internal reference at multiple points on the line. For example, it checks if the input is greater than 0; if not, it checks if it’s greater than the next number on the reference and keeps checking until it is. That point becomes the input number.

Analog Input

This exercise uses a potentiometer as an analog input. The potentiometer turns LED on the Arduino on and off when it is turned about halfway.

The components needed for this exercise are the following:

• 1 x Arduino Uno

• 1 x potentiometer

Figure 1-17 shows the components and Figure 1-18 shows the setup for the Arduino.

Open a new sketch. I called it chapter_01_3; and then copy the code from Listing 1-4.

int pinAnalogInput  =  A0;

int LEDOutput = 13;

int valueLight =  0;

void setup() {

  pinMode(LEDOutput, OUTPUT);

}

void loop() {

  valueLight =  analogRead(pinAnalogInput);

  if (valueLight < 500) {

    digitalWrite(LEDOutput, LOW);

  } else {

    digitalWrite(LEDOutput, HIGH);

  }

  delay(500);

}

Listing 1-4

chapter_01_3.ino

Verify the sketch and plug the USB back into your computer to upload the sketch to the Arduino. Now when you turn the potentiometer just past halfway, the LED on the Arduino should come off and on.

The code is very similar to the previous sketches in this chapter. The main difference is the variable for the analog pin int pinAnalogInput = A0; The analog input goes through pin A0;