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Voice Control LED Using Bluetooth

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Voice Control LED Using Bluetooth circuit diagram
Intermediate Robotics ⏱ 75 Minutes

Control an LED wirelessly using voice commands sent from a smartphone through Bluetooth. This introduces students to wireless control and smart-home applications, such as controlling lights, fans, and other devices remotely.

What You Will Learn

  • Serial communication over Bluetooth (HC-05)
  • Parsing single-character commands
  • Controlling two motors independently
  • Pairing and using a Bluetooth controller app

Components Required

Arduino UNO R3 HC-05 Bluetooth Module 5mm LED 220Ω Resistor 1kΩ Resistor 2kΩ Resistor Breadboard Jumper Wires
BUILD IT STEP BY STEP

Follow along and build with confidence.

Every step includes a visual reference and a plain-language explanation, so you always know what to do next.

STEP 01

Upload the Code

💻

This sketch listens for single-character commands over Bluetooth serial: F (forward), B (backward), L (left), R (right) and S (stop).

cpp 
#include <SoftwareSerial.h>

SoftwareSerial bluetooth(10, 11);

const int ledPin = 8;

void setup() {
  pinMode(ledPin, OUTPUT);
  digitalWrite(ledPin, LOW);

  Serial.begin(9600);
  bluetooth.begin(9600);
}

void loop() {
  if (bluetooth.available()) {
    char command = bluetooth.read();

    if (command == '1') {
      digitalWrite(ledPin, HIGH);
    }

    if (command == '0') {
      digitalWrite(ledPin, LOW);
    }
  }
}
STUCK ON SOMETHING?

Troubleshooting & common fixes.

Phone can't find the Bluetooth module.

Ensure the HC-05 is powered and its LED is blinking (searching mode); some modules need a first-time pairing directly from phone Bluetooth settings.

Car doesn't respond to commands.

Check TXD/RXD aren't swapped, and temporarily disconnect the HC-05 while uploading new code, since it shares the same serial pins as USB upload.

Car only goes forward, other commands don't work.

Confirm your controller app is sending single characters (F, B, L, R, S) and not full words or line-ending characters the switch statement doesn't expect.

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