Bluetooth Control App with MIT App Inventor – DIY Project

Have you ever wanted to control lights, fans, or any electronic device directly from your smartphone? With the power of MIT App Inventor and a simple microcontroller like the ESP32 or Arduino, you can build your own custom Internet of Things (IoT) application in just a few minutes.

The best part? You don’t need to be a professional programmer to do it.

I’ll walk you through creating a Bluetooth LED Control App. Whether you have an ESP32 (which uses Bluetooth Low Energy) or a classic Arduino Uno with an HC-05 module (which uses Classic Bluetooth), I’ve got you covered.

Why ESP32 is Better?

Whether you use an ESP32 or an Arduino Uno with an HC-05 module, we will build the same Android application with MIT App Inventor’s intuitive drag-and-drop interface.

The ESP32 is my go-to choice for this project, and here’s why:

Built-in Bluetooth: No need for external modules like HC-05 – everything is integrated
Dual-core processor: Handles complex tasks with ease
Wi-Fi capability: You can easily upgrade this project to IoT later
Cost-effective: Amazing value for the features you get

🧰 What You’ll Need?

Hardware Requirements:

ESP32 Development Board (e.g., ESP32 DevKit, NodeMCU-32S, or ESP32-C3).
Standard 5mm LED (any color)
220Ω or 330Ω resistor
Breadboard and jumper wires
Android smartphone for testing

If you want to use an Arduino board with an HC module:

Arduino Uno (or similar).
Bluetooth Module: HC-05 or HC-06 module.

Software Requirements:

Arduino IDE Download the latest version from arduino.cc.
A Google Account to log in to MIT App Inventor.

Step 1: Setting Up Your ESP32

If you haven’t used ESP32 with Arduino IDE before, follow these quick setup steps:

Open Arduino IDE
Go to File > Preferences
In the “Additional Board Manager URLs” field, add: https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json
Go to Tools > Board > Boards Manager
Search for “ESP32” and install the ESP32 platform by Espressif Systems
Select your ESP32 board from Tools > Board > ESP32 Device

Step 2: Circuit Diagram (ESP32/Arduino)

Most ESP32 development boards come with a built-in LED connected to GPIO 2. This is the same LED that blinks when you run the classic “Blink” example.

If you want to use an external LED, follow this circuit:

Connect the anode (long leg) of the LED to one end of the 220Ω resistor
Connect the other end of the resistor to any GPIO pin (Digital pin 22) on the ESP32
Connect the cathode (short leg) to the GND of the esp32

(Arduino + HC-05 Module Wiring):

The HC-05 is a popular Bluetooth module that adds wireless Bluetooth communication to Arduino.

HC-05 TX → Arduino Pin 0 (RX)
HC-05 RX → Arduino Pin 1 (TX)
HC-05 VCC → Arduino 5V
HC-05 GND → Arduino GND

You could control its built-in LED, which is connected to the PIN 13

Step 3: Complete Code

Now let’s upload the code that makes your ESP32 a BLE server. This code creates a Bluetooth device that advertises itself and listens for commands.

Open Arduino IDE, paste the following code, select your ESP32 board and port, then hit upload:

//#include <SoftwareSerial.h>
#include "BluetoothSerial.h"

const int ledPin = 2;

//SoftwareSerial MyBlue(0, 1);  // RX | TX
BluetoothSerial MyBlue;
char cmd;

void setup() {

  pinMode(ledPin, OUTPUT);

  //MyBlue.begin(9600);
  MyBlue.begin("ESP32-LED-Controller");
}

void loop() {

  // Bluetooth Control
  if (MyBlue.available()) {
    cmd = MyBlue.read();

    if (cmd == '1') {
      digitalWrite(ledPin, HIGH);
    } else if (cmd == '0') {
      digitalWrite(ledPin, LOW);
    }
  }

  delay(10);
}

Your ESP32 is now broadcasting! Keep it powered via USB.

For those who have Arduino boards and HC-05 modules, here’s a quick alternative:

#include <SoftwareSerial.h>

SoftwareSerial BT(0, 1); // RX, TX
const int ledPin = 13;
char command;

void setup() {
  Serial.begin(9600);
  BT.begin(9600);
  pinMode(ledPin, OUTPUT);
  Serial.println("Arduino Bluetooth Ready");
}

void loop() {
  if (BT.available()) {
    command = BT.read();
    if (command == '1') {
      digitalWrite(ledPin, HIGH);
      Serial.println("LED ON");
    }
    else if (command == '0') {
      digitalWrite(ledPin, LOW);
      Serial.println("LED OFF");
    }
  }
}

Step 4: Create the App with MIT

Now for the exciting part – creating your own Android app without writing a single line of complex code!

Create a New Project:

Go to MIT App Inventor
Click “Start a new project”
Name it ESP32_LED_Controller

Design the User Interface:

Let’s create a clean, professional-looking interface by using some components:

Device List (Picker)

Drag a ListPicker component
Change Text to Devices List
Set Width to “Fill parent”

Connection Status Label

Drag a Label
Set Text to “Not Connected”
Set FontSize to 16
TextColor to white

ON Button/OFF Button

Drag a HorizontalArrangement
Set Width to “Fill parent”
Set AlignHorizontal to “Center”

Inside the arrangement, add 2 Buttons
Set Text to “ON”/ “OFF” for each Button
Set BackgroundColor to green (On Button) / BackgroundColor to red (Off Button)
Set FontSize to 24 for both
Set Width to 150 pixels
Set Height to 80 pixels

BluetoothLE Component (non-visible)

From “Connectivity” in the palette, drag “BluetoothClient”
It will appear at the bottom under “Non-visible components”

Adding the Logic (Blocks):

Now switch to the Blocks view.

This is where we’ll program the behavior using visual blocks.

Block 1 (Before Picking): Scans for Devices

When the user clicks the “ListPicker” button, we start scanning for bluetooth devices and we display the founded devices during scanning:

Block 2 (After Picking): Connect to Selected Device

When the user selects a device from the list:

If connection is successful: We display “Connected” using Label1
But when connection is lost: We display “Not Connected” using Label1

Block 3/4(Button1, Button2): Send Commands

When ON button is clicked: we send the text “1”

When OFF button is clicked: we send the text “0”

Build and Install:

Now, head over to Build and Download APK file then install it using your smartphone.

Step 5: Testing Complete System

Now for the moment of truth!

Ensure your ESP32 is powered and running the Code (check Serial Monitor)
On your phone, Enable Bluetooth and Pair it with the ESP32 or Arduino HC Module
Open your app, and Click “Devices” – you should see “ESP32-LED-Controller” appear
Select your device from the list
Wait for connection – the status should be “Connected“
Press the ON button – the LED on GPIO 2 should light up!
Press the OFF button – the LED should turn off

Common Issues (troubleshooting)

ESP32 Not Found in Scan

Make sure the ESP32 is powered and the code is running (check Serial Monitor)
Try restarting the ESP32 by pressing the EN button
On your phone, make sure Bluetooth is enabled
Android sometimes requires location permission for Bluetooth scanning – grant it

Commands Not Working

Check the LED connection (polarity matters!)
Make sure GPIO 2 is correct for your board (some ESP32 variants use different pins)
Add debug prints in the ESP32 code to verify it’s receiving data

Conclusion

Congratulations! You’ve successfully built a complete Bluetooth-controlled LED system using the ESP32 as your main controller.

This project is just the beginning. The ESP32’s built-in BLE capability makes it perfect for countless IoT and home automation projects. With the app development skills you’ve learned in MIT App Inventor, you can now create custom controllers for anything you can imagine.

What will you control next? A robotic car? A smart home system? A wearable device? The possibilities are endless!

Bluetooth Control App with MIT App Inventor – DIY Project

Why ESP32 is Better?