Mission 17 · Stage 2

Electronic Dice

random() triggered by a button

Roll a random number 1–6 on a 7-segment display when you press a button.

Pin connections

Part 1		Part 2
Arduino pin 2	→	Roll button pin 1
Roll button pin 2	→	Arduino GND
Arduino pin 3	→	7-segment display seg A
Arduino pin 4	→	7-segment display seg B
Arduino pin 5	→	7-segment display seg C
Arduino pin 6	→	7-segment display seg D
Arduino pin 7	→	7-segment display seg E
Arduino pin 8	→	7-segment display seg F
Arduino pin 9	→	7-segment display seg G
7-segment display COM	→	Arduino GND

See it

Roll the dice with random()!

Press the button — random(1, 7) picks 1–6 on the display.

Board games and apps use random() for unpredictable outcomes.

The story

The problem

You want a new number each press, not a fixed pattern.

Think of it like

Like shaking a real die — you cannot guess the next value.

Meet the parts

Runs your sketch

Arduino

Brain

Loading part…

Triggers a new random roll

Roll button

Input

Loading part…

Shows die face 1–6

7-segment display

Display

Loading part…

How it works

Wait for press

Roll only when the player presses.

if (digitalRead(BUTTON_PIN) == LOW)

Pick random value

random(1, 7) gives 1 through 6 — perfect for a die.

int roll = random(1, 7);

Light segments

DIGITS[] table drives each segment ON/OFF for the number.

showDigit(roll);

Then loop back to step 1

Build the circuit

Follow these steps in order. Match the wires to the colors shown.

1
Place Arduino
Place the Arduino (uno) on the breadboard.
Arduino placed!
Loading part…
2
Place Roll button
Place the Roll button (btn1) on the breadboard.
Loading part…
3
Place 7-segment display
Place the 7-segment display (seg1) on the breadboard.
Loading part…
4
Connect Arduino pin 2 to Roll button (btn1) 1.l
Connect Arduino pin 2 to Roll button (btn1) 1.l.
5
Connect Roll button (btn1) 2.l to Arduino GND
Connect Roll button (btn1) 2.l to Arduino GND.
6
Connect Arduino pin 3 to 7-segment display (seg1) anode (+)
Connect Arduino pin 3 to 7-segment display (seg1) anode (+).
7
Connect Arduino pin 4 to 7-segment display (seg1) B
Connect Arduino pin 4 to 7-segment display (seg1) B.
8
Connect Arduino pin 5 to 7-segment display (seg1) cathode (-)
Connect Arduino pin 5 to 7-segment display (seg1) cathode (-).
9
Connect Arduino pin 6 to 7-segment display (seg1) D
Connect Arduino pin 6 to 7-segment display (seg1) D.
10
Connect Arduino pin 7 to 7-segment display (seg1) E
Connect Arduino pin 7 to 7-segment display (seg1) E.
11
Connect Arduino pin 8 to 7-segment display (seg1) F
Connect Arduino pin 8 to 7-segment display (seg1) F.
12
Connect Arduino pin 9 to 7-segment display (seg1) G
Connect Arduino pin 9 to 7-segment display (seg1) G.
13
Connect 7-segment display (seg1) COM.2 to Arduino GND
Connect 7-segment display (seg1) COM.2 to Arduino GND.

Try it

Press the button repeatedly — numbers 1–6 should change.
No fair guessing — random() decides!

Peek at code

Segment patterns

const uint8_t DIGITS[7] = {
  0b0000000,
  0b0000110,
  0b1011011,
  0b1001111,
  0b1100110,
  0b1101101,
  0b1111101,
};

Each digit is a bitmask — seven segments turn on/off to draw the number.

showDigit()

void showDigit(int digit) {
  uint8_t pattern = DIGITS[digit];
  for (int seg = 0; seg < 7; seg++) {
    digitalWrite(SEG_A + seg, (pattern >> seg) & 1);
  }
}

Loops segments and uses digitalWrite with bit math from the pattern.

Roll on button

void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    int roll = random(1, 7);
    showDigit(roll);
    while (digitalRead(BUTTON_PIN) == LOW) {
      delay(10);
    }
    delay(200);
  }
  delay(20);
}

Button triggers random(), then showDigit displays the result until next roll.

Show full sketch (electronic-dice.ino)

const int BUTTON_PIN = 2;
const int SEG_A = 3;
const uint8_t DIGITS[7] = {
  0b0000000,
  0b0000110,
  0b1011011,
  0b1001111,
  0b1100110,
  0b1101101,
  0b1111101,
};
void showDigit(int digit) {
  uint8_t pattern = DIGITS[digit];
  for (int seg = 0; seg < 7; seg++) {
    digitalWrite(SEG_A + seg, (pattern >> seg) & 1);
  }
}
void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  for (int i = 0; i < 7; i++) {
    pinMode(SEG_A + i, OUTPUT);
  }
  showDigit(1);
  randomSeed(analogRead(0));
}
void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    int roll = random(1, 7);
    showDigit(roll);
    while (digitalRead(BUTTON_PIN) == LOW) {
      delay(10);
    }
    delay(200);
  }
  delay(20);
}

Quick quiz

Q1. Where does repeating work belong?

A. loop() ✓
B. setup()
C. pinMode only

Why: Correct—loop() runs again and again.

Q2. What does random(1, 7) return?

A. 1 to 6 inclusive ✓
B. 1 to 7 inclusive
C. Always 3

Why: Correct — seven is excluded, giving six die faces.

Code lab — try on your own

Add a comment on randomSeed line explaining different rolls each run.
Hint: Line 24 in setup().
Change the post-roll delay(200) to delay(400).
Hint: Line 33 in loop().

Code walkthrough

A line-by-line tour of the sketch — the same steps as in Robo Gurukul Studio.

Program overview

Technical

Sketches have globals, then setup() once, then loop() forever.

In this project

Roll a random number 1–6 on a 7-segment display when you press a button.

Why here

Read from top to bottom. Hover words or lines for help!

const int BUTTON_PIN = 2;
const int SEG_A = 3;
const uint8_t DIGITS[7] = {
  0b0000000,
  0b0000110,
  0b1011011,
  0b1001111,
  0b1100110,
  0b1101101,
  0b1111101,
};
void showDigit(int digit) {
  uint8_t pattern = DIGITS[digit];
  for (int seg = 0; seg < 7; seg++) {
    digitalWrite(SEG_A + seg, (pattern >> seg) & 1);
  }
}

setup()

Technical

Runs one time when the board turns on.

In this project

Sets up pins and libraries for Electronic Dice.

Why here

One-time setup belongs here—not in loop().

void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  for (int i = 0; i < 7; i++) {
    pinMode(SEG_A + i, OUTPUT);
  }
  showDigit(1);
  randomSeed(analogRead(0));
}

loop()

Technical

Runs again and again after setup() is done.

In this project

This is the main action you see in Electronic Dice.

Why here

Repeating work (blink, read sensors) goes here.

void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    int roll = random(1, 7);
    showDigit(roll);
    while (digitalRead(BUTTON_PIN) == LOW) {
      delay(10);
    }
    delay(200);
  }
  delay(20);
}

Try this: Change numbers in loop(), then compile and run the simulator.

pinMode

Technical

Tells a pin if it listens or drives something.

In this project

Gets the Electronic Dice circuit ready in the simulator.

Why here

Goes in setup() because we only set pins once at the start.

  pinMode(BUTTON_PIN, INPUT_PULLUP);

digitalWrite

Technical

Turns a pin ON or OFF.

In this project

Controls lights, motors, or buzzers in Electronic Dice.

Why here

Goes in loop() so it can keep changing while the program runs.

    digitalWrite(SEG_A + seg, (pattern >> seg) & 1);

digitalRead

Technical

Checks if a pin is ON or OFF.

In this project

Reads buttons or sensors in Electronic Dice.

Why here

Goes in loop() so we can react when something changes.

  if (digitalRead(BUTTON_PIN) == LOW) {

analogRead

Technical

Reads a sensor number from 0 to 1023.

In this project

Turns a sensor signal into a number for Electronic Dice.

Why here

Goes in loop() to keep checking the sensor.

  randomSeed(analogRead(0));

delay

Technical

Waits for some time. Nothing else runs during the wait.

In this project

Controls speed so you can see Electronic Dice in the simulator.

Why here

Right after an action that should stay the same for a moment.

      delay(10);

random

Technical

Picks a random number in a range.

In this project

Adds randomness in Electronic Dice.

Why here

In loop() when you want different values each time.

    int roll = random(1, 7);

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