Source

Scott Fitzgerald and Michael Shiloh, The Arduino Projects Book Chapter 2: Spaceship Interface

Contents

Arduino board pins and electronic components connected to them

Assign board pins input/output roles.

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int inputPins[] = {2};
int outputPins[] = {LED_BUILTIN, 3, 4, 5};

After connecting breadboard pushbutton and LEDs to Arduino board pins, identify the pins here.

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int pushButton = 2;
int greenLED = 3;
int redLEDs[] = {4, 5};

Put breadboard LED pin states in an array for convenience.

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int ledStates[] = {HIGH, LOW};

Set starting state of breadboard pushbutton.

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int pushButtonState = LOW;

Helper functions

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void pulseLED(int pin, int delayTime) {
    for (int state : ledStates) {
        digitalWrite(pin, state);
        delay(delayTime);
    }
}

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void multiPulseLED(int pin, int pulses, int delayTime) {
    for (int i = 0; i < pulses; i++) {
        pulseLED(pin, delayTime);
        delay(delayTime);
    }
}

On button down, green LED off and alternately pulse red LEDS. On button up, green LED on and red LEDs off.

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void handlepushButtonState() {
    pushButtonState = digitalRead(pushButton);
    if (pushButtonState == HIGH) {     // button down
        digitalWrite(greenLED, LOW);
        for (int led : redLEDs) {
            multiPulseLED(led, 2, 25); // fast double pulse
        }
    } else {                           // button up
        digitalWrite(greenLED, HIGH);
        for (int led : redLEDs) {
            digitalWrite(led, LOW);
        }
    }
}

setup() and loop()

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void setup() {
    for (int pin : inputPins) pinMode(pin, INPUT);
    for (int pin : outputPins) pinMode(pin, OUTPUT);
    digitalWrite(greenLED, HIGH); // green LED on
}

void loop() {
    handlepushButtonState();
}