Press to Play

BRIEF Machines that listen

Until now your circuit has been a performer: it does its show whether you watch or not. Real machines are different. A console waits for the jump button. A kettle waits for the switch. Today you add the kit's most humble part, a little button, and suddenly your circuit has an input. It reacts to you. This is the half of electronics that makes games possible.

Time: 45–60 minutes · Difficulty: 2/5 · You need: Lessons 01 and 02 done.

KIT What you need

• R3 board with USB cable
• Breadboard
• 1 LED and its 220Ω resistor (the bodyguard, always)
• 1 push button (the small square one with four legs)
• Jumper wires

BUILD Wire it

Unplug the USB first. The button's four legs come in two joined pairs; the legs on the same side of the little gap are connected to each other. Push the button in so it straddles the middle channel of the breadboard, it clicks in flat.

From	To	Why
R3 pin 4	Button leg (top-left)	The listening wire
Button leg (bottom-left)	R3 GND	Pressing connects pin 4 to ground
R3 pin 13	Resistor → LED long leg	Same faithful light as Lesson 01
LED short leg	R3 GND	Loop complete

Two legs of the button do all the work. If your button seems to be "always pressed", you have used two legs from the same joined pair, move one wire to the other side of the gap.

CODE Program it

Type it, don't paste it. Meet the most important word in programming: if.

// GAMERIFT Beginner Kit, Lesson 03: Press to Play
// Your first machine that listens and decides.

const int buttonPin = 4;
const int lightPin  = 13;

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);  // listen, with the built-in pull-up on
  pinMode(lightPin, OUTPUT);         // speak
}

void loop() {
  int state = digitalRead(buttonPin);  // what does the pin hear right now?

  if (state == LOW) {            // LOW means PRESSED (upside-down logic!)
    digitalWrite(lightPin, HIGH);  // light on while held
  } else {
    digitalWrite(lightPin, LOW);   // light off when released
  }
}

1. Upload it.
2. Hold the button: light on. Let go: light off.
3. Notice there is no delay() anywhere, loop() runs thousands of times a second, checking the button each time. Your board is very attentive.

BREAK IT Now break it on purpose

1. Pull the button's GND wire out and wave your hand near the wires. With the pull-up on, the light should stay politely off. Now change INPUT_PULLUP to INPUT in the code and upload. Watch the light flicker to ghost presses, that is a floating pin. Change it back and respect the pull-up forever.
2. Swap the if. Make it if (state == HIGH). Now the light is on until you press. You just made a "release detector". Some machines really work this way (fridge door light, for one).
3. Press really, really fast. Can you beat loop()? (You cannot. It checks the pin about 100,000 times per second.)

REMIX Make it yours

• The toggle: press once for on, press again for off, like a real light switch. Hint: you need a variable that remembers, declared above setup(), and a small delay(250) after each press so one press doesn't count five times.
• Two-button duel: wire a second button on pin 5 and a second LED on pin 12. First player to press lights their lamp. You have built a game-show buzzer.
• Secret knock: the light only comes on if you hold the button for three whole seconds. Hint: when the press starts, count with delay() in small steps and check the button is still down.

LOG IT Show and tell

Film 15 seconds of your remix and save it for your lesson log, the final build (Lesson 12) submission loves a good journey. Stuck? Send a photo of your wiring via contact us, a real person will spot the crossed leg.