Count On Me

BRIEF The oldest digital number in the world

Microwave clocks, petrol pumps, scoreboards, lift buttons: the seven-segment display has been showing humanity its numbers since before your parents were born. It is nothing but seven little LED bars arranged as an 8. Light the right bars and any digit appears. Today you wire all seven, teach your board the shapes of the digits, and build a counter that ticks up every time you press a button. This is the most wires you have ever used. Go slow. It is worth it.

Time: 60–75 minutes · Difficulty: 4/5, mostly patience · You need: Lesson 03 done (buttons).

KIT What you need

• R3 board with USB cable
• Breadboard
• The 7-segment display (the little red window with 10 legs)
• 1 × 220Ω resistor
• 1 push button
• Lots of jumper wires, count out nine before you start

BUILD Wire it

Unplug the USB. Straddle the display across the breadboard's middle channel like you did with the button. Wire the shared ground first, then work through the bars one by one, ticking them off on paper.

From	To	Why
Bottom middle leg	220Ω resistor → R3 GND	Shared ground, one bodyguard for all
R3 pin 3	Leg for bar a (top row, right of middle)	Top bar
R3 pin 4	Leg for bar b (top row, far right)	Top right
R3 pin 5	Leg for bar c (bottom row, right of middle)	Bottom right
R3 pin 6	Leg for bar d (bottom row, second from left)	Bottom bar
R3 pin 7	Leg for bar e (bottom row, far left)	Bottom left
R3 pin 8	Leg for bar f (top row, second from left)	Top left
R3 pin 9	Leg for bar g (top row, far left)	The middle bar
R3 pin 10	Button leg · other leg to GND	The counting trigger, like Lesson 03

Leg layouts can differ between displays. If a digit comes out scrambled later, don't rewire in a panic, use the Break It section's "bar test" to map YOUR display, then swap the wires calmly.

CODE Program it

// GAMERIFT Beginner Kit, Lesson 07: Count On Me
// An array holds the shape of every digit. The button counts.

const int barPins[7] = {3, 4, 5, 6, 7, 8, 9};  // bars a,b,c,d,e,f,g
const int buttonPin = 10;

// The digit table: one row per digit, one 1/0 per bar (a to g).
const int digits[10][7] = {
  {1,1,1,1,1,1,0},  // 0
  {0,1,1,0,0,0,0},  // 1
  {1,1,0,1,1,0,1},  // 2
  {1,1,1,1,0,0,1},  // 3
  {0,1,1,0,0,1,1},  // 4
  {1,0,1,1,0,1,1},  // 5
  {1,0,1,1,1,1,1},  // 6
  {1,1,1,0,0,0,0},  // 7
  {1,1,1,1,1,1,1},  // 8
  {1,1,1,1,0,1,1}   // 9
};

int count = 0;

void showDigit(int n) {
  for (int i = 0; i < 7; i++) {
    digitalWrite(barPins[i], digits[n][i]);   // look it up, light it up
  }
}

void setup() {
  for (int i = 0; i < 7; i++) {
    pinMode(barPins[i], OUTPUT);
  }
  pinMode(buttonPin, INPUT_PULLUP);
  showDigit(0);
}

void loop() {
  if (digitalRead(buttonPin) == LOW) {   // pressed (upside-down, remember)
    count = count + 1;
    if (count > 9) count = 0;            // only one digit, wrap around
    showDigit(count);
    delay(250);                           // so one press counts once
  }
}

1. Upload. A zero appears. Press the button: 1, 2, 3... past 9 it rolls back to 0.
2. Look how short loop() is. The array did the heavy lifting, that is the power of a good table.

BREAK IT Now break it on purpose

1. The bar test. In setup(), light just barPins[0] and see which bar glows. Is it really the top one? Test all seven one at a time and draw your display's true map. If any wires are swapped, this is how you find them, no guessing.
2. Pull out one bar's wire (say, bar g) and count to 9. Watch 8 become 0 and 4 become... something sad. One missing segment scrambles half the alphabet, which is why a half-dead petrol pump display is so confusing.
3. Delete the delay(250) and press once. The counter sprints, one press registered fifty times. Now you have seen why debouncing matters, put it back.

REMIX Make it yours

• Countdown: start at 9, tick DOWN once per second on its own, and flash all bars when it hits 0. Rocket launch. (No button needed.)
• Dice: each press shows a random number 1 to 6. Hint: random(1, 7). Board-game night is saved forever.
• Score keeper: your Lesson 03 second button on pin 11: one button adds, one subtracts. Real scoreboard logic.

LOG IT Show and tell

Film your counter counting for your lesson log, this build earns bragging rights, it has more wires than everything before it combined. Stuck? Photo of your wiring to contact us.