Day 21: Dual-Mode Control — IR Remote + Sound

Hi Anish! Today is integration day. You’re going to take the IR remote from Day 19, the sound sensor from Day 20, and the LCD from Days 15-18, and mash them into a single sketch that has two modes:

• MANUAL mode — IR remote controls the LED directly. Clap detection is off.
• AUTO mode — claps toggle the LED. Remote switches modes but doesn’t control the LED.

One remote button switches between modes. The LCD shows which mode you’re in. No new concepts today — just combining everything you already know.

What you need today

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• Arduino Uno + USB cable
• Breadboard
• IR receiver (Day 19)
• Sound sensor (Day 20)
• LCD with I2C (Day 15)
• 1 LED + 220Ω resistor
• Jumper wires

This is a lot of components on one breadboard. Take your time. Test each subsystem alone first if you’re not sure it’s wired right.

The circuit

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graph TB
    subgraph Power["Power & LCD"]
      V5["5V"]
      GND["GND"]
      A4["A4 → LCD SDA"]
      A5["A5 → LCD SCL"]
    end
    subgraph IR["IR receiver"]
      V5 --> IRV["IR VCC"]
      GND --> IRG["IR GND"]
      PIN11["Pin 11"] --> IRO["IR OUT"]
    end
    subgraph Sound["Sound sensor"]
      V5 --> SV["Sound VCC"]
      GND --> SG["Sound GND"]
      PIN2["Pin 2"] --> SD["Sound D0"]
    end
    subgraph LED["LED"]
      PIN8["Pin 8"] --> R220["220Ω"] --> LEDp["LED"] --> GND
    end

Pin assignments:

• Pin 2 — Sound sensor digital output
• Pin 8 — LED
• Pin 11 — IR receiver OUT
• A4/A5 — LCD I2C

Power rails (5V and GND) on the breadboard shared by all three modules.

The code

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#include <IRremote.hpp>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// Pin assignments
const int LED_PIN   = 8;
const int SOUND_PIN = 2;
const int IR_PIN    = 11;

// === YOUR remote codes — from Day 19 ===
const int MODE_BTN_CODE   = 0x45;  // e.g., Power button — toggles mode
const int LED_ON_CODE     = 0x40;  // e.g., Vol Up — turns LED on in manual
const int LED_OFF_CODE    = 0x19;  // e.g., Vol Down — turns LED off in manual

// Mode: false = MANUAL, true = AUTO
bool autoMode = false;

// Sound debouncing
int lastClapTime = 0;

LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(SOUND_PIN, INPUT);
  Serial.begin(9600);

  IrReceiver.begin(IR_PIN);

  lcd.init();
  lcd.backlight();
  showMode();
}

void loop() {
  handleIR();
  if (autoMode) {
    handleSound();
  }
}

// === Handles IR button presses ===
void handleIR() {
  if (IrReceiver.decode()) {
    int code = IrReceiver.decodedIRData.command;
    Serial.print("IR code: 0x");
    Serial.println(code, HEX);

    if (code == MODE_BTN_CODE) {
      autoMode = !autoMode;
      showMode();
    } else if (code == LED_ON_CODE && !autoMode) {
      digitalWrite(LED_PIN, HIGH);
    } else if (code == LED_OFF_CODE && !autoMode) {
      digitalWrite(LED_PIN, LOW);
    }

    IrReceiver.resume();
  }
}

// === Handles clap detection (only in auto mode) ===
void handleSound() {
  if (digitalRead(SOUND_PIN) == HIGH) {
    int now = millis();
    if (now - lastClapTime > 300) {    // ignore echoes
      digitalWrite(LED_PIN, !digitalRead(LED_PIN));
      Serial.println("Clap -> toggle");
      lastClapTime = now;
    }
  }
}

// === Updates the LCD to show current mode ===
void showMode() {
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Mode:");
  lcd.setCursor(0, 1);
  lcd.print(autoMode ? "AUTO (clap)" : "MANUAL (remote)");
}

Upload. You should see:

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Mode:
MANUAL (remote)

Press the mode button on the remote → display changes to:

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2

Mode:
AUTO (clap)

Clap → LED toggles. Press the mode button again → back to manual. Press vol-up on remote → LED on. Press vol-down → LED off. In auto mode, the remote volume buttons do nothing (only clap works).

What’s worth noticing

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No new language features, but three important patterns are on display. Look at the loop():

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void loop() {
  handleIR();
  if (autoMode) {
    handleSound();
  }
}

That’s it. Three lines. No giant blob of code. The actual work is broken out into three helper functions: handleIR(), handleSound(), showMode(). The loop() just coordinates them.

Pattern 1: Small loop(), big helpers

#

A good Arduino loop() should read almost like English: “Handle IR. If we’re in auto mode, handle sound. Done.” Each helper function does exactly one job. This is the structure real embedded engineers use — it’s also how you’ll organize the final project on Day 25.

If your loop() starts to grow past ~20 lines, it’s usually a sign you should break a chunk out into a helper function.

Pattern 2: Mode-dependent behavior

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if (autoMode) {
  handleSound();
}

We skip the entire sound handler when we’re in manual mode. Why? Because in manual mode, we don’t WANT sound to do anything. Instead of wrapping the sound handling with an if deep inside handleSound(), we decide at the loop() level whether to call it at all.

Inside handleIR(), we do something similar:

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} else if (code == LED_ON_CODE && !autoMode) {
  digitalWrite(LED_PIN, HIGH);
}

The && !autoMode means: “only turn on the LED from a remote button IF we’re in manual mode.” In auto mode, the volume buttons are ignored. The && (AND) operator from Day 7.

Pattern 3: Non-blocking sound detection with millis()

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void handleSound() {
  if (digitalRead(SOUND_PIN) == HIGH) {
    int now = millis();
    if (now - lastClapTime > 300) {
      digitalWrite(LED_PIN, !digitalRead(LED_PIN));
      lastClapTime = now;
    }
  }
}

Notice there’s no delay() in the sound handler. Instead, we track when the last clap happened with lastClapTime (a global variable), and ignore any new sound for 300ms after the last valid one.

Why? Because a delay(300) would also stall the IR handler — you wouldn’t be able to receive remote presses during those 300ms. Using millis() means both handlers run simultaneously without blocking each other.

This is the cornerstone of writing Arduino code that handles multiple things at once. You’ll see it again and again.

Try this

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1. Show the last action. Add a third row of LCD info — print “Last: remote” or “Last: clap” depending on what just happened.
2. Clap-to-mode. Map a triple clap to change modes (Day 20 clap counter pattern). No more fumbling for the remote.
3. Servo control. Replace the LED with a servo (Day 12). In manual mode, remote buttons rotate the servo. In auto mode, each clap nudges it by 10°.
4. Sound meter fallback. In auto mode, if there’s been no clap for 30 seconds, turn the LED off automatically (like an auto-off bedside lamp).

What you learned today

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• How to integrate multiple subsystems (IR + Sound + LCD + LED) into one sketch
• How to keep loop() clean by using helper functions
• How to gate behavior by mode with if (mode) and && !mode checks
• Why delay() is bad when multiple things need to run at once
• Using millis() to debounce without blocking
• The skeleton of a real embedded program: mode state + multiple handlers + display

What is next

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Day 22 — we take everything and wrap it into the Smart Room System, the grand project of the sensor chapter. LCD status, IR remote for modes, claps for triggers, LDR for auto-darkness, buzzer for alerts. It’s a lot, but you already know how to do every piece.

Great work, Anish. You just shipped your most complex sketch yet.