SparkFun Inventor's Kit Experiment Guide - v4.0

Contributors: Joel_E_B
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Circuit 2B: Digital Trumpet

Learn about digital inputs and buttons as you build your own digital trumpet!


Parts Needed

Grab the following quantities of each part listed to build this circuit:


New Components


Buttons, also known as momentary switches, are switches that only remain in their on state as long as they’re being actuated, or pressed. Most often momentary switches are best used for intermittent user-input cases: reset button and keypad buttons. These switches have a nice, tactile, “clicky” feedback when you press them.

multicolored buttons

Note that the different colors are just aesthetic. All of the buttons included behave the same no matter their color.

New Concepts

Binary Number System

Number systems are the methods we use to represent numbers. We’ve all been mostly operating within the comfy confines of a base-10 number system, but there are many others. The base-2 system, otherwise known as binary, is common when dealing with computers and electronics. There are really only two ways to represent the state of anything: ON or OFF, HIGH or LOW, 1 or 0. And so, almost all electronics rely on a base-2 number system to store and manipulate numbers. The heavy reliance electronics places on binary numbers means it’s important to know how the base-2 number system works.

Digital Input

In circuit 1A, you worked with digital outputs. This circuit focuses on digital inputs. Digital inputs only care if something is in one of two states: TRUE or FALSE, HIGH or LOW, ON or OFF. Digital inputs are great for determining if a button has been pressed or if a switch has been flipped.

Pull-up Resistors

A pull-up resistor is a small circuit that holds the voltage HIGH (5V) on a pin until a button is pressed, pulling the voltage LOW (0V). The most common place you will see a pull-up resistor is when working with buttons. A pull-up resistor keeps the button in one state until it is pressed. The RedBoard has built-in pull-up resistors, but they can also be added to a circuit externally. This circuit uses the internal pull-up resistors, covered in more detail in the Code to Note section.

Hardware Hookup

Buttons are not polarized. However, they do merit a closer look. Buttons make momentary contact from one connection to another, so why are there four legs on each button? The answer is to provide more stability and support to the buttons in your breadboard circuit. Each row of legs is connected internally. When the button is pressed, one row connects to the other, making a connection between all four pins.

button pins explained

If the button's legs don't line up with the slots on the breadboard, rotate it 90 degrees.

Ready to start hooking everything up? Check out the circuit diagram and hookup table below to see how everything is connected.

Circuit Diagram


Having a hard time seeing the circuit? Click on the image for a closer look.

Hookup Table

Component RedBoard Breadboard Breadboard Breadboard
Buzzer J1 (Buzzer + ) J3 (Buzzer - )
Potentiometer B1 B2 B3
Jumper Wire GND GND Rail ( - )
Jumper Wire Digital Pin 10 F1
Jumper Wire E2 GND Rail ( - )
Jumper Wire E1 F3
Push Button D16/D18 G16/G18
Push Button D22/D24 G22/G24
Push Button D28/D30 G28/G30
Jumper Wire Digital Pin 4 J18
Jumper Wire Digital Pin 3 J24
Jumper Wire Digital Pin 2 J30
Jumper Wire J16 GND Rail ( - )
Jumper Wire J22 GND Rail ( - )
Jumper Wire J28 GND Rail ( - )

In the table, polarized components are shown with a warning triangle and the whole row highlighted yellow.

Open the Sketch

To open the code, go to: File > Examples > SIK_Guide_Code-V_4 > SIK_Circuit_2B-ButtonTrumpet

You can also copy and paste the following code into the Arduino IDE. Hit upload, and see what happens!

  SparkFun Inventor’s Kit
  Circuit 2B-ButtonTrumpet

  Use 3 buttons plugged to play musical notes on a buzzer.

  This sketch was written by SparkFun Electronics, with lots of help from the Arduino community.
  This code is completely free for any use.

  View circuit diagram and instructions at:
  Download drawings and code at:

//set the pins for the button and buzzer
int firstKeyPin = 2;
int secondKeyPin = 3;
int thirdKeyPin = 4;

int buzzerPin = 10;

void setup() {
  //set the button pins as inputs
  pinMode(firstKeyPin, INPUT_PULLUP);
  pinMode(secondKeyPin, INPUT_PULLUP);
  pinMode(thirdKeyPin, INPUT_PULLUP);

  //set the buzzer pin as an output
  pinMode(buzzerPin, OUTPUT);

void loop() {

  if (digitalRead(firstKeyPin) == LOW) {      //if the first key is pressed
    tone(buzzerPin, 262);                     //play the frequency for c
  else if (digitalRead(secondKeyPin) == LOW) { //if the second key is pressed
    tone(buzzerPin, 330);                     //play the frequency for e
  else if (digitalRead(thirdKeyPin) == LOW) { //if the third key is pressed
    tone(buzzerPin, 392);                     //play the frequency for g
  else {
    noTone(buzzerPin);                        //if no key is pressed turn the buzzer off

  note  frequency
  c     262 Hz
  d     294 Hz
  e     330 Hz
  f     349 Hz
  g     392 Hz
  a     440 Hz
  b     494 Hz
  C     523 Hz

What You Should See

Different tones will play when you press different keys. Turning the potentiometer will adjust the volume.


Program Overview

  1. Check to see if the first button is pressed. a. If it is, play the frequency for c. b. If it isn’t, skip to the next else if statement.
  2. Check to see if the second button is pressed. a. If it is, play the frequency for e. b. If it isn’t, skip to the next else if statement.
  3. Check to see if the second button is pressed. a. If it is, play the frequency for g. b. If it isn’t, skip to the next else if statement.
  4. If none of the if statements are true a. Turn the buzzer off.

Code to Note

Internal Pull-Up Resistor:
pinMode(firstKeyPin, INPUT_PULLUP);
To declare a standard input, use the line pinMode(pin_name, INPUT). If you would like to use one of the RedBoard's built-in pull-up 20kΩ resistors, it would look like this: pinMode(firstKeyPin, INPUT_PULLUP);. The advantage of external pull-ups is being able to choose a more exact value for the resistor.
Digital Input:
Check to see if an input pin is reading HIGH (5V) or LOW (0V). Returns TRUE (1) or FALSE (0) depending on the reading.
Is Equal to:
if(digitalRead(firstKeyPin) == LOW)
This is another logical operator. The 'is equal to' symbol (==) can be confusing. Two equals signs are equivalent to asking, "Are these two values equal to one another?" On the other hand, one equals sign in code is assigning a particular variable to a value. Don't forget to add the second equals sign if you are comparing two values.

Coding Challenges

Change the key of each buttonUse the frequency table in the comment section at the end of the code to change the notes that each button plays.
Play more than three notes with if statementsBy using combinations of buttons, you can play up to seven notes of the scale. You can do this in a few ways. To get more practice with if statements, try adding seven if statements and using the Boolean AND (&&) operator to represent all of the combinations of keys.
Play more than three notes with binary mathYou can use a clever math equation to play more than three notes with your three keys. By multiplying each key by a different number, then adding up all of these numbers, you can make a math equation that produces a different number for each combination of keys.


The buzzer is too loud or too quietTurn the potentiometer to adjust the volume.
The RedBoard thinks one key is always pressedCheck your wiring. You may have ground and 5V backward if one or more buttons behave as though they're pressed all the time.
The buttons are not workingFirst, make sure that the wiring is correct. It is easy to misalign a wire with a button leg. Second, make sure that you have declared your buttons as inputs and have enabled the internal pull-up resistors with INPUT_PULLUP.