# 🌡️ 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:

* `RaspberryPi4_PinMap.jpeg`
* `TZCBIN8qL-HTU21D-Module-Pinout.png`

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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

```bash
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

```bash
sudo apt update
# Updates package list

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

---

### ⚙️ 3. Enable I2C

```bash
sudo raspi-config
# Opens Raspberry Pi configuration menu
```

Go to:

```
Interfacing Options → I2C → Enable
```

```bash
sudo reboot
# Restarts system to apply changes
```

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### 🔍 4. Verify Sensor

```bash
i2cdetect -y 1
# Scans I2C bus for connected devices
```

Expected:

```
0x40
```

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### 🧑‍💻 5. Compile the Sensor Program

```bash
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

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

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

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### 🔐 7. Set Permissions

```bash
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

```bash
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

```bash
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

```bash
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:

```javascript
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

```bash
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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