Guard Dog

BRIEF The invisible torch

Shop doors that ding when you walk in. Taps that run when your hands arrive. Robot vacuums that stop before hitting the wall. All of them use the same trick: shine an invisible light, watch for its reflection. Your kit's IR obstacle module is that trick on one small board, an infrared torch and an infrared eye, side by side. When something comes close, its reflection lands in the eye and the module shouts. Today you build a desk guard that notices an approaching hand and raises an alarm, the exact skill your final build needs.

Time: 45–60 minutes · Difficulty: 3/5 · You need: Lessons 08 and 10 done (buzzer, sensor tuning).

KIT What you need

• R3 board with USB cable
• Breadboard
• The IR obstacle module (the one with TWO clear bulbs on the front, one dark, one clear, and a blue dial)
• The active buzzer (the sealed one with the sticker)
• 1 LED and its 220Ω resistor
• Jumper wires

BUILD Wire it

Unplug the USB. Module pins into the breadboard, read the labels on YOUR board (usually OUT, GND, VCC).

From	To	Why
Module OUT pin	R3 pin 7	The detection wire
Module VCC pin	R3 5V	Power for torch and eye
Module GND pin	R3 GND	Ground
R3 pin 8	Active buzzer + leg · − leg to GND	The bark
R3 pin 13	220Ω resistor → LED long leg · short leg to GND	The visual alarm

Point the module's two bulbs out across your desk, not at a nearby wall, or it will "detect" the wall forever.

CODE Program it

// GAMERIFT Beginner Kit, Lesson 11: Guard Dog
// Something comes close: flash and bark until it leaves.

const int eyePin    = 7;
const int buzzerPin = 8;
const int lampPin   = 13;

void setup() {
  pinMode(eyePin, INPUT);
  pinMode(buzzerPin, OUTPUT);
  pinMode(lampPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  if (digitalRead(eyePin) == LOW) {     // LOW = something is there (active low!)
    Serial.println("INTRUDER!");
    digitalWrite(lampPin, HIGH);        // flash...
    digitalWrite(buzzerPin, HIGH);      // ...and bark
    delay(100);
    digitalWrite(lampPin, LOW);
    digitalWrite(buzzerPin, LOW);
    delay(100);                          // on-off-on-off = urgent
  } else {
    digitalWrite(lampPin, LOW);         // all clear, stand down
    digitalWrite(buzzerPin, LOW);
  }
}

1. Upload. Slide your hand toward the module. At some distance, the guard erupts.
2. Tune the blue dial (tiny turns!) until it triggers at roughly a hand-span away. The module's own little LED shows you the trigger point even before your code reacts.
3. Walk away and let it guard your snacks. It does not blink. It does not get bored. This is why factories love machines.

BREAK IT Now break it on purpose

1. Test dark vs light objects. A white page triggers it from further away than a black sleeve, dark things swallow infrared instead of reflecting it. Real robot vacuums genuinely struggle with black carpets for exactly this reason.
2. Point it at a sunny window. Sunlight is full of infrared and can blind or falsely trigger the eye. Where you place a sensor matters as much as the sensor.
3. Film the transmitter bulb with your phone while the module is powered. See the faint glow your eyes cannot? You are looking at the invisible torch itself.

REMIX Make it yours

• Silent mode: add the tilt switch (that little metal cylinder in your kit) in series or read it as an input: desk guard tipped on its side = quiet patrol, LED only. Stand it up = full alarm.
• The escalator: the longer the intruder stays, the faster and angrier the beeping gets. Hint: shrink the delay a little on every alarm cycle, and reset it when clear.
• Friendly mode: swap the bark for Lesson 08's melody, a shop-door chime that greets instead of accuses. Same machine, opposite personality, one line of difference.

LOG IT Show and tell

Film the moment your hand triggers the guard for your lesson log. You now know every skill the final build needs. Stuck? Contact us with a photo.