🌡️ Raspberry Pi 4 Temperature & Humidity Monitoring System (HTU21D)

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📌 Project Overview

This project implements a real-time temperature and humidity monitoring system using a Raspberry Pi 4 and an HTU21D sensor. The system reads environmental data via I2C, processes it using a C program, and displays the results on a web dashboard using Nginx.

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🧠 System Architecture

HTU21D Sensor → I2C → C Program → JSON File → Nginx → Web Browser

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🧰 Materials

🔧 Hardware

• Raspberry Pi 4
• HTU21D sensor
• Jumper wires (female-to-female)
• MicroSD card with Raspberry Pi OS
• Power supply

💻 Software

• Raspberry Pi OS / Debian
• GCC compiler
• i2c-tools
• libi2c-dev
• Nginx
• Git

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🔌 Hardware Connections

📷 Pin Reference Images

Include these images in your repository:

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📍 Wiring Table

HTU21D	Raspberry Pi 4
VCC	3.3V
GND	GND
SDA	GPIO2 (SDA)
SCL	GPIO3 (SCL)

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🚀 Deployment Guide (From Scratch)

📥 1. Clone the Repository

git clone http://<GITEA_SERVER>/<USER>/<REPOSITORY>.git
# Downloads the project from the server

cd <REPOSITORY>
# Enters the project folder

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🧰 2. Install Dependencies

sudo apt update
# Updates package list

sudo apt install gcc i2c-tools libi2c-dev nginx git
# Installs compiler, I2C tools, web server, and Git

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⚙️ 3. Enable I2C

sudo raspi-config
# Opens Raspberry Pi configuration menu

Go to:

Interfacing Options → I2C → Enable

sudo reboot
# Restarts system to apply changes

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🔍 4. Verify Sensor

i2cdetect -y 1
# Scans I2C bus for connected devices

Expected:

0x40

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🧑‍💻 5. Compile the Sensor Program

cd sensors/HTU21D
# Move to sensor source code

gcc main.c htu21d.c -o HTU21D -li2c
# Compiles the program and links I2C library

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📂 6. Deploy Web Files

sudo cp -r ~/basic-ui-dashboard/* /var/www/html/
# Copies project files to Nginx directory

sudo mkdir -p /var/www/html/data
# Creates folder for JSON output

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🔐 7. Set Permissions

sudo chmod +x /var/www/html/sensors/HTU21D/HTU21D
# Allows execution of sensor program

sudo chown -R www-data:www-data /var/www/html
# Gives Nginx access to files

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▶️ 8. Run Sensor Loop

cd /var/www/html
# Go to web directory

while true; do ./sensors/HTU21D/HTU21D > data/HTU21D.json; sleep 5; done
# Continuously updates JSON every 5 seconds

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🌐 9. Start Nginx

sudo systemctl start nginx
# Starts web server

sudo systemctl enable nginx
# Enables auto-start on boot

sudo systemctl status nginx
# Verifies server is running

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🌍 10. Get Raspberry Pi IP

hostname -I
# Displays local IP address

Example:

192.168.1.100

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🖥️ 11. Access from Another Computer

Open a browser and go to:

http://192.168.1.100

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🔄 Real-Time Updates

JavaScript fetch:

fetch('./data/HTU21D.json?nocache=' + Date.now())

What it does:

• Prevents browser cache
• Forces fresh data request

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🧪 How to Use

1. Power on Raspberry Pi
2. Connect sensor
3. Run sensor loop
4. Open browser
5. Monitor values in real time

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⚠️ Troubleshooting

❌ No data update

• Check loop is running
• Verify nocache in fetch

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❌ Permission denied

sudo nano /var/www/html/index.html
# Edit file with admin privileges

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❌ Sensor not detected

• Check wiring
• Run i2cdetect

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📈 Improvements

• WebSockets (real-time without polling)
• Database storage
• Historical charts
• Remote access via internet

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🎯 Conclusion

This project integrates:

• Embedded systems (sensor + Raspberry Pi)
• C programming
• Linux system configuration
• Web development (Nginx + JS)

It demonstrates a complete pipeline from hardware acquisition to real-time web visualization.

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