3. Digital Input: Button

This lesson uses: Arduino UNO R3 board, TinkerBlock TK04 Push Button module, TinkerBlock TK01 XL LED module, jumper wires (or breadboard). Use the button as digital input; learn to combine digitalRead() with digitalWrite(). Outcome: press the button and the LED turns on; release and it turns off.

1. Wiring

• TK04 button: VCC → 5V, GND → GND, SIGNAL → D2, NC leave unconnected
• TK01 LED: GND → GND, SIGNAL → D13 (in code 13 is this pin; button uses 2)

Wire the button and LED as in the diagram below.

2. New sketch

1. Arduino IDE: File → New (or Ctrl/Cmd + N) to create a blank sketch
2. Confirm board and port are selected (same as Lesson 01)
3. Type the code below into the default setup() and loop() yourself

3. Program structure

Same as last lesson: two fixed blocks setup() and loop().

• setup(): Tell the board “pin 2 is for reading the button, pin 13 is for the LED”; runs once.
• loop(): Keep repeating “read pin 2 to get state → use if to decide: if state means ‘pressed’ then turn LED on, else turn LED off → short delay (debounce)”.
• if chooses which block runs depending on whether the condition is true or false, so the program can react to the button.

4. Code to write

Type the code below line by line into setup() and loop() (do not copy-paste; typing it yourself helps you remember):

// Button on D2, LED on D13: read button state, on when pressed, off when released
#define BUTTON_PIN 2    // button SIGNAL to D2
#define LED_PIN 13      // LED SIGNAL to D13

void setup() {
  pinMode(BUTTON_PIN, INPUT);   // D2 as input, to read button
  pinMode(LED_PIN, OUTPUT);     // D13 as output, to control LED
}

void loop() {
  int state = digitalRead(BUTTON_PIN);   // TK04 is HIGH when pressed, LOW when released

  if (state == HIGH) {                   // condition true means button pressed
    digitalWrite(LED_PIN, HIGH);          // pressed: LED on
  } else {
    digitalWrite(LED_PIN, LOW);           // released: LED off
  }
  delay(100);   // short delay to reduce mis-triggers from mechanical bounce (simple debounce)
}

About if and else

• What is a condition
  A condition is something that can be true or false. Here state == HIGH is a condition: when state equals HIGH the condition is true, otherwise false.
  Note: two equals == means “compare for equality”; one = is assignment. Writing if (state = HIGH) is a logic error.

• if (condition) { ... }
  When the condition in parentheses is true, run the code in the curly braces; if false, skip that block and see if there is an else.

• else { ... }
  Must come right after an if. When the if condition is false, the code in the else block runs. So each time only one of the if block or else block runs, never both.

• In this lesson
  state == HIGH means “button pressed”. So: when pressed the if block runs (LED on); when released the else block runs (LED off).

Once that’s clear, type the code in; press the button and the LED turns on, release and it turns off—you’ll see if-else in action.

Program notes

Overall idea: In loop() we first read the level on D2 with digitalRead (HIGH or LOW); then if (state == HIGH) — if true, LED on; else LED off. Use two equals == for comparison; one = is assignment and will cause wrong behavior.

5. Hands-on

1. After entering the code, click Verify (✓) to compile
2. Click Upload (→) to upload to the board
3. Button controls LED: When you press TK04, TK01 turns on; when you release, it turns off

Expected result:

Proceed to Lesson 04 (or the first module lesson).

6. Common issues

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