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266 lines
5.4 KiB
Markdown
266 lines
5.4 KiB
Markdown
# Raspberry Pi 4 Temperature & Humidity Monitoring System (HTU21D)
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---
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## Project Overview
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The Temperature-Humidity-Sensor is the first module in a series of sensors for GNU/Linux intended for the construction of weather microstations that will be responsible for measuring air quality.
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This module monitors temperature and humidity in real time using a Raspberry Pi 4 and an HTU21D sensor. The sensor reads the environmental data, sends it via I2C, processes it with a C program, and displays the results on a web dashboard using Nginx.
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---
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## Objective
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The objective is to learn about the development of drivers to establish communication between a sensor (hardware) responsible for collecting data and a set of programs (software) that process this data, design a target compatible with a Raspberry Pi to create weather microstations responsible for monitoring air quality, and learn to design and implement electronic circuits.
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In addition to the objective of completing the Delfin program stay and obtaining new skills and knowledge to further develop my professional career.
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---
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## System Architecture
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The module is designed as a simple data channel where we connect the sensor HTU21D to a web interface for real-time data visualization.
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As follows:
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HTU21D Sensor → I2C → C Program → JSON File → Nginx → Web Browser
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The sensor collects temperature and humidity data, sends it via the I2C Protocol to a Raspberry Pi 4, which reads and converts it into temperature and humidity values using a C program,then stores them in a JSON file. Nginx serves this file along with the web interface (HTML), where a JavaScript script fetches the data and updates the displayed values in real time.
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---
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## Materials
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### Hardware
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* Raspberry Pi 4
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* HTU21D sensor
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* Jumper wires (female-to-female)
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* MicroSD card with Raspberry Pi OS
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* Power supply
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### Software
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* Raspberry Pi OS / Debian
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* GCC compiler
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* i2c-tools
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* libi2c-dev
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* Nginx
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* Git
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---
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## Hardware Connections
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### Pin Reference Images
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---
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### Wiring Table
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| HTU21D | Raspberry Pi 4 |
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| ------ | -------------- |
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| VCC | 3.3V |
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| GND | GND |
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| SDA | GPIO2 (SDA) |
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| SCL | GPIO3 (SCL) |
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---
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## Deployment Guide
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### 1. Install Dependencies
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```bash
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sudo apt update
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# Updates package list
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sudo apt install gcc i2c-tools libi2c-dev nginx git
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# Installs compiler, I2C tools, web server, and Git
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```
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---
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### 2. Clone the Repository
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```bash
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git clone https://gitea.itmorelia.com/Verano-Delfin-2026/Temperature-Humidity-Sensor.git
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# Downloads the project from the server
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cd Temperature-Humidity-Sensor
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# Enters the project folder
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```
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---
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### 3. Enable I2C
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```bash
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sudo raspi-config
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# Opens Raspberry Pi configuration menu
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```
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Go to:
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```
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Interfacing Options → I2C → Enable
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```
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```bash
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sudo reboot
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# Restarts system to apply changes
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```
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---
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### 4. Verify Sensor
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```bash
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i2cdetect -y 1
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# Scans I2C bus for connected devices
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```
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Expected:
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```
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Warning: Can't use SMBus Quick Write command, will skip some addresses
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0 1 2 3 4 5 6 7 8 9 a b c d e f
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00:
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10:
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20:
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30: -- -- -- -- -- -- -- --
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40: 40 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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60:
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70:
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```
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This output indicates that the sensor is connected at address 0x40.
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If the device is not detected and the output looks like this:
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```
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Warning: Can't use SMBus Quick Write command, will skip some addresses
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0 1 2 3 4 5 6 7 8 9 a b c d e f
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00:
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10:
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20:
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30: -- -- -- -- -- -- -- --
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40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
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60:
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70:
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```
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The sensor may still be connected. Some I2C devices do not respond to SMBus probing commands used by i2cdetect.
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In this case, you can try to directly read from the device address.
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To read the temperature, send the measurement command (0xE3 for hold mode or 0xF3 for no hold mode) and then read two bytes of data:
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```bash
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sudo i2cget -y 1 0x40 0xE3 w
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```
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If you receive a hexadecimal value (e.g., 0x3871), the sensor is properly connected and working.
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---
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### 5. Compile the Sensor Program
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```bash
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cd sensors/HTU21D
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# Move to sensor source code
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gcc main.c htu21d.c -o HTU21D -li2c
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# Compiles the program and links I2C library
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```
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---
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### 6. Deploy Web Files
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```bash
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sudo cp -r ~/Temperature-Humidity-Sensor/* /var/www/html/
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# Copies project files to Nginx directory
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```
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```bash
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sudo mkdir -p /var/www/html/data
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# Creates folder for JSON output
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```
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---
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### 7. Set Permissions
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```bash
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sudo chmod +x /var/www/html/sensors/HTU21D/HTU21D
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# Allows execution of sensor program
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sudo chown -R www-data:www-data /var/www/html
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# Gives Nginx access to files
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```
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---
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### 8. Run Sensor Loop
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```bash
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cd /var/www/html
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# Go to web directory
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while true; do ./sensors/HTU21D/HTU21D > data/HTU21D.json; sleep 5; done
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# Continuously updates JSON every 5 seconds
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```
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---
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### 9. Start Nginx
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```bash
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sudo systemctl start nginx
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# Starts web server
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sudo systemctl enable nginx
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# Enables auto-start on boot
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sudo systemctl status nginx
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# Verifies server is running
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```
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---
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### 10. Get Raspberry Pi IP
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```bash
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hostname -I
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# Displays local IP address
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```
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Example:
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```
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192.168.1.100
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```
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---
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### 11. Access from Another Computer
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Open a browser and go to:
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```
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http://192.168.1.100
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```
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---
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### 12. Result
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---
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