Published July 18, 2025 © GPL3+

Control Room Lamp via HC-05 Using.NET WinForms

Wirelessly control a lamp in your room using a C#.NET WinForms app and an HC-05 Bluetooth module—simple, smart, and fun!

ExpertFull instructions provided1 hour74

Control Room Lamp via HC-05 Using.NET WinForms

Things used in this project

Hardware components

Arduino Nano R3

ControlEverything.com High-Power Relay Shield for Particle Photon I²C 1-Channel SPDT 10-Amp

HC-05 Bluetooth Module

Jumper wires (generic)

Software apps and online services

Microsoft Visual Studio 2017

Arduino IDE

Hand tools and fabrication machines

Multitool, Screwdriver

Story

It all started with a simple question: Can I control the lamp in my room wirelessly using just my laptop?As someone deeply interested in both software development and embedded systems, I decided to combine the best of both worlds.

So, I picked up my Arduino Nano, paired it with an HC-05 Bluetooth module, and decided to write a C#.NET Windows Forms application as the remote controller. My goal was to build something real, useful, and fun — and most importantly, something that could inspire others to explore the exciting intersection of hardware and software.

🧠 What I Did:

I designed a simple UI in Windows Forms with ON and OFF buttons.

I designed a simple UI in Windows Forms with ON and OFF buttons.

Connected the HC-05 module to the Arduino, which communicates with the laptop wirelessly via Bluetooth.

Connected the HC-05 module to the Arduino, which communicates with the laptop wirelessly via Bluetooth.

🔧 COM Port Detection Challenge:

One of the trickiest parts of the project was managing the COM port assignment for the HC-05 Bluetooth module. Every time it paired with my PC, it could potentially be assigned a different COM port — which caused issues in my WinForms application since I had the port manually hardcoded.

Instead of coding a dynamic port selector, I took a more straightforward approach:

I opened Control Panel → Devices and Printers → Hardware Properties

I opened Control Panel → Devices and Printers → Hardware Properties

Located the HC-05 module and checked the COM port assigned to it

Located the HC-05 module and checked the COM port assigned to it

Then I updated my code to use that COM port value

Then I updated my code to use that COM port value

This manual process worked well during development, but it taught me a valuable lesson — in real-world applications, dynamic port detection and proper error handling are essential for robustness and user-friendliness.

Code

void setup() {
  pinMode(2, OUTPUT);  // Built-in LED
  Serial.begin(9600);
}

void loop() {
  if (Serial.available()) {
    char command = Serial.read();
    if (command == '1') {
      digitalWrite(2, HIGH); // Turn ON LED
    } else if (command == '0') {
      digitalWrite(2, LOW);  // Turn OFF LED
    }
  }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
//using System.Windows.Forms;
//using System;
using System.IO.Ports;
using System.Windows.Forms;

namespace WinFormLed
{
    public partial class Form1 : Form
    {
        SerialPort serialPort = new SerialPort();
        public Form1()
        {
            InitializeComponent();
            serialPort.PortName = "COM9";
            serialPort.BaudRate = 9600;

            try
            {
                serialPort.Open();
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error opening COM9: " + ex.Message);
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
        private void button1_Click(object sender, EventArgs e)
        {
            
        }

        private void button2_Click(object sender, EventArgs e)
        {
            
        }
        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (serialPort.IsOpen)
                serialPort.Close();
        }

        private void button1_Click_1(object sender, EventArgs e)
        {
            if (serialPort.IsOpen)
            {
                serialPort.Write("1"); // Turn ON LED
                //MessageBox.Show("Sent '1' to COM9"); // Debug line
                MessageBox.Show("BULB IS TURNED OFF, DEAR AKASH YANAKANDLA");
            }
        }

        private void button2_Click_1(object sender, EventArgs e)
        {
            if (serialPort.IsOpen)
            {
                serialPort.Write("0"); // Turn OFF LED
                //MessageBox.Show("Sent '0' to COM9"); // Debug line
                MessageBox.Show("BULB IS TURNED ON, DEAR AKASH YANAKANDLA");
            }
        }
    }
}