# Air Quality Monitor
**Air Quality Monitor** is a lightweight web interface that displays real-time data from two environmental sensors: **HTU21D** and **BMP180**. The system uses **NGINX** to serve an HTML page that reads live data from JSON files.
All the system is runing on a beagle bone black.
## Project Description
This project was designed to visualize environmental parameters in a simple, fast, and efficient way using an embedded graphical interface. The data is obtained from the following sensors:
- **HTU21D**: Temperature and relative humidity.
- **BMP180**: Atmospheric pressure and temperature.
The data is stored in two JSON files, updated by the embedded system and displayed through an HTML/JavaScript-based frontend.
---
## Project Structure
UI directory
- BMP180.json # Pressure and temperature data from BMP180
- HTU21D.json # Temperature and humidity data from HTU21D
- index.html # Main web interface
- index.js # JavaScript logic to fetch and display JSON data
- style.css # Custom CSS styles
> The `.json` files are automatically updated by C programs that communicate with the sensors via I2C witch the librarys integrated on the repository.
---
## Conection of the sensors with Beagle bone.
Both sensors that we are using are conected to the I2C port 2 of the beagle bone in parallel(P9-19 and P9-20):
## 🚀 Installation & Deployment with NGINX
### Requirements
- Linux server with `nginx` installed.
- Root access or permission to modify NGINX configuration.
### Steps
1. Install NGINX (if not already installed):
```bash
sudo apt update
sudo apt install nginx
```
2. Copy the project files to NGINX’s public directory (e.g., /var/www/html):
``` bash
```
3. Redirect the configuration file to our repository folder:
```bash
sudo vi /etc/nginx/sites-available/default
```
4. Replace the line:
```bash
root /var/www/html;
```
with:
```bash
root /home/debian/path/to/your/repository;
```
5. Apply chages with:
```bash
sudo systemctl restart nginx
```
## User interface
This is a simple web page that displays real-time sensor data from two devices:
- BMP180: Shows temperature and pressure.
- HTU21D: Shows humidity and temperature.
It’s styled with a separate CSS file (style.css) and fetches live data using JavaScript (index.js), which likely reads values from two JSON files (BMP180.json and HTU21D.json).
### HTML
#### Complete code
```html
Sensor Dashboard
Sensor Dashboard
BMP180
Temperature: -- °CPressure: -- hPa
HTU21D
Humidity: -- %Temperature: -- °C
```
#### Explanation
```html
```
- Declares this document as HTML5.
- lang="en" sets the document language to English, which is useful for accessibility and SEO.
##### HEAD
```html
Sensor Dashboard
```
- charset="UTF-8" ensures proper text encoding.
- viewport makes the layout responsive on mobile devices.
- title is what appears in the browser tab.
- link imports the external CSS file (style.css) for styling.
##### BODY
```html
...
```
- The background div might be used for a visual effect like a background image or color gradient (defined in your CSS).
- container holds the main content (dashboard).
- index.js is loaded at the end to ensure the DOM is ready before scripts run.
##### Dashboard Title
```html
Sensor Dashboard
```
- This is the main heading of your web page.
##### Sensor Card: BMP180
```hmtl
BMP180
Temperature: -- °CPressure: -- hPa
```
- This block represents the BMP180 sensor.
- The icon (from flaticon.com) visually represents pressure/temperature.
- The id attributes (temperature, pressure) are hooks used by JavaScript to insert real values from BMP180.json.
##### Sensor Card: HTU21D
```html
HTU21D
Humidity: -- %Temperature: -- °C
```
- This block represents the HTU21D sensor.
- The image is a humidity icon.
- The id attributes (humidity, tempHTU) are also updated by JavaScript using HTU21D.json.
##### JavaScript Integration
```hmtl
```
- This line loads your script, which is responsible for:
- Fetching the JSON files.
- Parsing their content.
- Replacing the placeholder values (-- °C, -- hPa, etc.) with live sensor data.
### Index.js
The script fetches data from two local JSON files:
- BMP180.json — contains temperature and pressure.
- HTU21D.json — contains temperature and humidity.
Then it updates the HTML every 3 seconds so the page always shows live sensor values.
#### Full code
```js
function updateBMP180() {
fetch('BMP180.json')
.then(res => res.json())
.then(data => {
document.getElementById('temperature').textContent = `Temperature: ${data.temperature.toFixed(2)} °C`;
document.getElementById('pressure').textContent = `Pressure: ${data.pressure.toFixed(2)} hPa`;
})
.catch(err => console.error("Error BMP180:", err));
}
function updateHTU21D() {
fetch('HTU21D.json')
.then(res => res.json())
.then(data => {
document.getElementById('humidity').textContent = `Humidity: ${data.humidity.toFixed(1)} %`;
document.getElementById('tempHTU').textContent = `Temperature: ${data.temperature.toFixed(1)} °C`;
})
.catch(err => console.error("Error HTU21D:", err));
}
setInterval(() => {
updateBMP180();
updateHTU21D();
}, 3000);
// Carga inicial
updateBMP180();
updateHTU21D();
```
### Code explanation
#### Function: updateBMP180
```js
function updateBMP180() {
fetch('BMP180.json')
.then(res => res.json())
.then(data => {
document.getElementById('temperature').textContent = `Temperature: ${data.temperature.toFixed(2)} °C`;
document.getElementById('pressure').textContent = `Pressure: ${data.pressure.toFixed(2)} hPa`;
})
.catch(err => console.error("Error BMP180:", err));
}
```
- This defines a new function named updateBMP180. You’ll call this function when you want to update the BMP180 sensor data on the page.
- fetch('BMP180.json'): Loads the JSON file from the same directory.
- .then(res =\>json()): Parses the response as JSON
- .then(data +\> {}): Accesses the data inside the file.
- document.getElementById(...) updates the corresponding elements in your HTML.
#### Function: updateHTU21D
```js
function updateHTU21D() {
fetch('HTU21D.json')
.then(res => res.json())
.then(data => {
document.getElementById('humidity').textContent = `Humidity: ${data.humidity.toFixed(1)} %`;
document.getElementById('tempHTU').textContent = `Temperature: ${data.temperature.toFixed(1)} °C`;
})
.catch(err => console.error("Error HTU21D:", err));
}
```
Works the same way as updateBMP180(), but:
- Fetches from HTU21D.json.
- Displays humidity and temperature.
- Uses .toFixed(1) for 1 decimal place (common for humidity values).
#### Auto-update every 3 seconds
```js
setInterval(() => {
updateBMP180();
updateHTU21D();
}, 3000);
```
- Calls both update functions every 3,000 milliseconds (3 seconds).
- Keeps the UI in sync with new sensor readings, assuming the .json files are being updated continuously.
#### Initial load
```js
updateBMP180();
updateHTU21D();
```
- Ensures the data is shown immediately on page load, before the 3-second interval kicks in.
### CSS
#### Full code
```css
* {
margin: 0;
padding: 0;
box-sizing: border-box;
font-family: "Segoe UI", sans-serif;
}
body, html {
height: 100%;
background-color: #0d1117;
color: #ffffff;
position: relative;
overflow: hidden;
}
.background {
background-image: url('https://wallpapers.com/images/hd/blue-circuit-board-traces-zn0xezd4t8axj9r6.webp');
background-size: cover;
background-position: center;
opacity: 0.1;
filter: blur(3px);
position: absolute;
top: 0; left: 0;
width: 100%;
height: 100%;
z-index: -1;
}
.container {
max-width: 800px;
margin: 40px auto;
background-color: #161b22;
padding: 30px;
border-radius: 20px;
box-shadow: 0 0 30px rgba(0, 255, 255, 0.2);
animation: fadeIn 1s ease-in;
}
h1 {
text-align: center;
margin-bottom: 30px;
font-size: 2.5rem;
color: #58a6ff;
}
.sensor-card {
background-color: #1f2937;
padding: 20px;
border-radius: 15px;
margin-bottom: 20px;
box-shadow: 0 0 20px rgba(100, 255, 255, 0.1);
animation: slideIn 1s ease;
display: flex;
flex-direction: column;
align-items: center;
text-align: center;
}
.sensor-card img {
width: 64px;
height: 64px;
margin-bottom: 10px;
}
.sensor-card h2 {
margin-bottom: 10px;
color: #90cdf4;
}
.data span {
display: block;
margin: 5px 0;
font-size: 1.2rem;
color: #ffffff;
}
@keyframes fadeIn {
from { opacity: 0; transform: translateY(-20px); }
to { opacity: 1; transform: translateY(0); }
}
@keyframes slideIn {
from { opacity: 0; transform: scale(0.9); }
to { opacity: 1; transform: scale(1); }
}
```
#### Explaining
Global Styling
- *: Resets default browser spacing (margin, padding) and sets a consistent font and box model across the entire page.
- body, html:
- Sets full height layout.
- Applies a dark background (#0d1117) with white text.
- Hides overflow and enables positioning for internal layers.
⸻
Background Layer
- .background:
- Adds a faint, blurred circuit board image as the background.
- Uses opacity: 0.1 and filter: blur(3px) to give it a soft tech feel.
- Positioned absolutely behind everything (z-index: -1).
⸻
Main Container
- .container:
- A centered, card-like section with:
- A dark background (#161b22)
- Rounded corners and soft glowing shadow.
- Padding and a fade-in animation on load.
⸻
Title
- h1:
- Large, centered header in light blue (#58a6ff).
- Styled to stand out at the top of the dashboard.
⸻
Sensor Cards
- .sensor-card:
- Styled boxes for each sensor.
- Darker background (#1f2937) with a soft shadow.
- Rounded corners, padding, and a slide-in animation when they load.
- Contents are centered vertically and horizontally.
- .sensor-card img:
- Sensor icons sized to 64×64 pixels with margin for spacing.
- .sensor-card h2:
- Sub-headers for each sensor card in a soft blue (#90cdf4).
⸻
Data Text
- .data span:
- Each line of sensor data (e.g., temperature, humidity).
- Displayed as blocks with spacing and larger font for visibility.
⸻
Animations
- @keyframes fadeIn:
- Smooth slide-down + fade-in for the container.
- @keyframes slideIn:
- Subtle zoom-in effect for each sensor card.
## Sensor library
### HTU21D library
The library contains 3 files, HTU21D.c, htu21d.h and main.c
#### htu21d.h
```h
#ifndef HTU21D_H
#define HTU21D_H
// HTU21D i2c address
#define HTU21D_ADDR 0x40
//commands for readings
#define HTU21D_TEMP 0xE3
#define HTU21D_HUM 0xE5
#define HTU21D_RESET 0xFE
//funtion declarations
//Temp:
int getTemp(int fd, double *temp);
//HUM
int getHum(int fd, double *hum);
//RESET
int getReset(int fd);
#endif
```
##### Explanation
- HTU21D_ADDR: The I2C address of the sensor (0x40).
- HTU21D_TEMP: Command to read temperature (0xE3).
- HTU21D_HUM: Command to read humidity (0xE5).
- HTU21D_RESET: Command to reset the sensor (0xFE).
- Declares three functions:
1. getTemp() – for reading temperature,
2. getHum() – for reading humidity,
3. getReset() – for resetting the sensor.
#### HTU21D.c
```c
#include
#include
#include
//Aditional librarys
#include
#include
#include "htu21d.h"
#define I2C_PATH "/dev/i2c-%d"
#define I2C_PORT 2
int main(){
char filePath[20];
snprintf(filePath, sizeof(filePath), I2C_PATH, I2C_PORT );
int fd = open(filePath, O_RDWR);
if(fd<0){
fprintf(stderr, "Error: Unable to access HTU21D sensor: %s",strerror(errno));
exit(-1);
}
//measurements
double temperature=0;
double humidity=0;
if((getTemp(fd, &temperature)<0)||(getHum(fd, &humidity)<0)){
fprintf(stderr,"Error -404: Measurments not read");
exit(-1);
}
//printf("HTU21D Module \n");
//printf("%5.2fC \n", temperature);
//printf("%5.2fC \n", humidity);
printf("{");
printf("\"temperature\": %5.2f,", temperature);
printf("\"humidity\": %5.2f", humidity);
printf("}");
return 0;
}
```
##### Explanation
###### Librarys
```c
#include
#include
#include
#include
#include
#include "htu21d.h"
```
These headers provide:
- unistd.h: basic system calls (like read, write, etc.)
- sys/ioctl.h: lets you control devices (e.g., set I2C slave address)
- linux/i2c-dev.h: allows interaction with the I2C bus
- i2c/smbus.h: provides high-level SMBus/I2C functions like i2c_smbus_read_i2c_block_data
- stdio.h: for printing error messages
- "htu21d.h": includes your own header file (constants and function declarations)
###### getTemp() Function
```c
int getTemp(int fd, double *temp) {
getReset(fd); // Resets the sensor before reading
char buffer[3]; // Buffer to hold 3 bytes of data from sensor
__s32 res = i2c_smbus_read_i2c_block_data(fd, HTU21D_TEMP, 3, buffer);
```
- Calls getReset(fd) to ensure the sensor is in a clean state before reading.
- Uses i2c_smbus_read_i2c_block_data to read 3 bytes from the sensor using the temperature command 0xE3.
- These 3 bytes contain raw temperature data + CRC (which you ignore here).
```c
if (res < 0) {
perror("ERROR-1: Failed to read Temperature");
return -1;
}
```
- If the read fails (e.g., I2C communication issue), it prints an error and returns -1.
```c
*temp = -46.85 + 175.72 * (buffer[0] * 256 + buffer[1]) / 65536.0;
return 0;
}
```
- The first two bytes in buffer are combined to make a 16-bit raw temperature.
- The formula from the HTU21D datasheet is applied to convert raw data into actual temperature in Celsius.
- The result is stored in the variable pointed to by *temp.
- Returns 0 to indicate success.
###### getHum() Function
This function is nearly identical to getTemp(), but it reads humidity instead.
```c
int getHum(int fd, double *hum) {
getReset(fd);
char buffer[3];
__s32 res = i2c_smbus_read_i2c_block_data(fd, HTU21D_HUM, 3, buffer);
```
- Uses the command HTU21D_HUM (value 0xE5) to read humidity data.
```c
if (res < 0) {
perror("ERROR -3: Failed to read Humidity");
return -1;
}
*hum = -6 + 125 * (buffer[0] * 256 + buffer[1]) / 65536.0;
return 0;
}
```
- Applies the formula from the datasheet to convert the raw bytes to % humidity.
###### getReset() Function
```c
int getReset(int fd) {
if (0 > ioctl(fd, I2C_SLAVE, HTU21D_ADDR)) {
perror("ERROR -2: Failed in reset");
return -2;
}
i2c_smbus_write_byte(fd, HTU21D_RESET);
return 0;
}
```
- ioctl() tells the I2C driver which slave device you want to talk to (address 0x40).
- Then i2c\_smbus\_write\_byte() sends the reset command 0xFE to the HTU21D.
- Resets the sensor, which is sometimes necessary to avoid bad reads or stuck states.
### BMP180 library
The library contains 3 files, bmp180.c, bmp180.h and main.c
#### bmp180.c
```c
#include "bmp180.h"
#include
#include
#include
#include
#include
#define BMP180_ADDR 0x77
// Lectura de 16 bits de un registro (dos bytes)
static int read16(int fd, uint8_t reg, int16_t *value) {
uint8_t buf[2];
if (write(fd, ®, 1) != 1) return -1;
if (read(fd, buf, 2) != 2) return -1;
*value = (buf[0] << 8) | buf[1];
return 0;
}
// Escritura de 8 bits a un registro
static int write8(int fd, uint8_t reg, uint8_t value) {
uint8_t buf[2] = {reg, value};
if (write(fd, buf, 2) != 2) return -1;
return 0;
}
// Leer calibración desde el sensor
int bmp180_init(int fd, bmp180_calib_data_t *calib) {
if (read16(fd, 0xAA, &calib->AC1) < 0) return -1;
if (read16(fd, 0xAC, &calib->AC2) < 0) return -1;
if (read16(fd, 0xAE, &calib->AC3) < 0) return -1;
if (read16(fd, 0xB0, (int16_t*)&calib->AC4) < 0) return -1;
if (read16(fd, 0xB2, (int16_t*)&calib->AC5) < 0) return -1;
if (read16(fd, 0xB4, (int16_t*)&calib->AC6) < 0) return -1;
if (read16(fd, 0xB6, &calib->B1) < 0) return -1;
if (read16(fd, 0xB8, &calib->B2) < 0) return -1;
if (read16(fd, 0xBA, &calib->MB) < 0) return -1;
if (read16(fd, 0xBC, &calib->MC) < 0) return -1;
if (read16(fd, 0xBE, &calib->MD) < 0) return -1;
return 0;
}
// Leer temperatura sin procesar (raw temp)
static int bmp180_read_raw_temperature(int fd, int32_t *raw_temp) {
if (write8(fd, 0xF4, 0x2E) < 0) return -1; // start temp measurement
usleep(4500); // esperar 4.5 ms
int16_t value;
if (read16(fd, 0xF6, &value) < 0) return -1;
*raw_temp = value;
return 0;
}
// Leer presión sin procesar (raw pressure)
static int bmp180_read_raw_pressure(int fd, int32_t *raw_press, int oss) {
if (write8(fd, 0xF4, 0x34 + (oss << 6)) < 0) return -1; // start pressure measurement
usleep(25000); // esperar 25 ms para oss=0 (simple oversampling)
uint8_t buf[3];
uint8_t reg = 0xF6;
if (write(fd, ®, 1) != 1) return -1;
if (read(fd, buf, 3) != 3) return -1;
*raw_press = ((buf[0] << 16) | (buf[1] << 8) | buf[2]) >> (8 - oss);
return 0;
}
int bmp180_read_temperature(int fd, bmp180_calib_data_t *calib, double *temperature) {
int32_t UT;
if (bmp180_read_raw_temperature(fd, &UT) < 0) return -1;
int32_t X1 = ((UT - calib->AC6) * calib->AC5) >> 15;
int32_t X2 = (calib->MC << 11) / (X1 + calib->MD);
int32_t B5 = X1 + X2;
*temperature = ((B5 + 8) >> 4) / 10.0;
return 0;
}
int bmp180_read_pressure(int fd, bmp180_calib_data_t *calib, double *pressure) {
int oss = 0; // oversampling setting 0..3
int32_t UP;
if (bmp180_read_raw_pressure(fd, &UP, oss) < 0) return -1;
// Recalcular B5 para temperatura, necesario para presión
int32_t UT;
if (bmp180_read_raw_temperature(fd, &UT) < 0) return -1;
int32_t X1 = ((UT - calib->AC6) * calib->AC5) >> 15;
int32_t X2 = (calib->MC << 11) / (X1 + calib->MD);
int32_t B5 = X1 + X2;
int32_t B6 = B5 - 4000;
X1 = (calib->B2 * ((B6 * B6) >> 12)) >> 11;
X2 = (calib->AC2 * B6) >> 11;
int32_t X3 = X1 + X2;
int32_t B3 = (((calib->AC1 * 4 + X3) << oss) + 2) >> 2;
X1 = (calib->AC3 * B6) >> 13;
X2 = (calib->B1 * ((B6 * B6) >> 12)) >> 16;
X3 = ((X1 + X2) + 2) >> 2;
uint32_t B4 = (calib->AC4 * (uint32_t)(X3 + 32768)) >> 15;
uint32_t B7 = ((uint32_t)UP - B3) * (50000 >> oss);
int32_t p;
if (B7 < 0x80000000) {
p = (B7 << 1) / B4;
} else {
p = (B7 / B4) << 1;
}
X1 = (p >> 8) * (p >> 8);
X1 = (X1 * 3038) >> 16;
X2 = (-7357 * p) >> 16;
p = p + ((X1 + X2 + 3791) >> 4);
*pressure = p / 100.0; // Pa a hPa (mbar)
return 0;
}
```
##### explanation
###### Headers and defines
```c
#include "bmp180.h"
#include
#include
#include
#include
#include
#define BMP180_ADDR 0x77
```
- Includes standard and I2C Linux headers.
- Defines the I2C address of the BMP180 sensor.
###### read16() – Read 16-bit (2-byte) value from a register
```c
static int read16(int fd, uint8_t reg, int16_t *value)
```
- Sends the register address via write().
- Reads 2 bytes and stores the result as a big-endian 16-bit signed integer.
- Used to read calibration values and sensor data.
###### write8() – Write 8-bit value to a register
```c
static int write8(int fd, uint8_t reg, uint8_t value)
```
- Sends 2 bytes: register address and value.
- Used to trigger temperature or pressure measurements by writing command codes to control register 0xF4
###### bmp180\_init() – Read all calibration data from sensor
```c
int bmp180_init(int fd, bmp180_calib_data_t *calib)
```
- Reads 11 calibration values from registers 0xAA to 0xBF.
- These are factory-set and unique to each sensor.
- Needed to apply temperature and pressure compensation formulas correctly.
###### bmp180\_read\_raw\_temperature() – Trigger and read unprocessed temperature
```c
static int bmp180_read_raw_temperature(int fd, int32_t *raw_temp)
```
- Writes 0x2E to control register 0xF4 to start temperature conversion.
- Waits 4.5 ms (conversion time).
- Reads result from 0xF6 and 0xF7.
###### bmp180\_read\_raw\_pressure() – Trigger and read unprocessed pressure
```c
static int bmp180_read_raw_pressure(int fd, int32_t *raw_press, int oss)
```
- Writes 0x34 + (oss << 6) to register 0xF4 to start pressure conversion.
- Waits 25 ms for conversion (OSS=0).
- Reads 3 bytes from 0xF6, 0xF7, 0xF8 and shifts them to get a 19-bit value.
- oss (oversampling setting) affects resolution and delay.
###### bmp180\_read\_temperature() – Convert raw temperature to °C
```c
int bmp180_read_temperature(int fd, bmp180_calib_data_t *calib, double *temperature)
```
- Uses raw temperature and calibration data.
- Follows Bosch’s datasheet compensation formula:
X1 = ((UT - AC6) * AC5) >> 15
X2 = (MC << 11) / (X1 + MD)
B5 = X1 + X2
T = (B5 + 8) >> 4 → gives temperature in 0.1°C
- Final result is divided by 10.0 to get °C.
###### bmp180\_read\_pressure() – Convert raw pressure to hPa
```c
int bmp180_read_pressure(int fd, bmp180_calib_data_t *calib, double *pressure)
```
- Uses raw pressure and temperature (needed for B5).
- Applies long compensation formula from datasheet:
1. Many intermediate steps using calibration values.
2. Computes B3, B4, B6, B7, X1, X2, X3, and finally p.
- Final pressure p is in Pa; divide by 100.0 to get hPa (mbar).
#### bmp180.h
```c
#ifndef BMP180_H
#define BMP180_H
#include
typedef struct {
int16_t AC1, AC2, AC3;
uint16_t AC4, AC5, AC6;
int16_t B1, B2;
int16_t MB, MC, MD;
} bmp180_calib_data_t;
int bmp180_init(int fd, bmp180_calib_data_t *calib);
int bmp180_read_temperature(int fd, bmp180_calib_data_t *calib, double *temperature);
int bmp180_read_pressure(int fd, bmp180_calib_data_t *calib, double *pressure);
#endif
```
##### Explanation
###### Header
```h
#ifndef BMP180_H
#define BMP180_H
#include
```
- Header guard to prevent multiple inclusion.
- Includes standard integer types (uint8_t, int16_t, etc.).
###### Structure: bmp180\_calib\_data\_t
```h
typedef struct {
int16_t AC1, AC2, AC3;
uint16_t AC4, AC5, AC6;
int16_t B1, B2;
int16_t MB, MC, MD;
} bmp180_calib_data_t;
```
- Holds all calibration constants (11 total).
- Types match datasheet: some are signed, others unsigned.
###### Function declarations
```h
int bmp180_init(int fd, bmp180_calib_data_t *calib);
int bmp180_read_temperature(int fd, bmp180_calib_data_t *calib, double *temperature);
int bmp180_read_pressure(int fd, bmp180_calib_data_t *calib, double *pressure);
```
#### main.c
```c
#include
#include
#include
#include
#include
#include "bmp180.h"
#define I2C_BUS "/dev/i2c-2"
#define BMP180_ADDR 0x77
int main() {
int fd = open(I2C_BUS, O_RDWR);
if (fd < 0) {
perror("Error abriendo el bus I2C");
return 1;
}
if (ioctl(fd, I2C_SLAVE, BMP180_ADDR) < 0) {
perror("Error configurando la dirección I2C");
close(fd);
return 1;
}
bmp180_calib_data_t calib;
if (bmp180_init(fd, &calib) < 0) {
fprintf(stderr, "Error leyendo datos de calibración BMP180\n");
close(fd);
return 1;
}
double temperature, pressure;
if (bmp180_read_temperature(fd, &calib, &temperature) < 0) {
fprintf(stderr, "Error leyendo temperatura BMP180\n");
close(fd);
return 1;
}
if (bmp180_read_pressure(fd, &calib, &pressure) < 0) {
fprintf(stderr, "Error leyendo presión BMP180\n");
close(fd);
return 1;
}
printf("{\"temperature\": %.2f, \"pressure\": %.2f}\n", temperature, pressure);
close(fd);
return 0;
}
```
##### Explanation
###### Open I2C Bus
```c
int fd = open("/dev/i2c-2", O_RDWR);
```
- Opens I2C device for read/write.
###### Set I2C Slave Address
```c
ioctl(fd, I2C_SLAVE, BMP180_ADDR);
```
- Tells the kernel which I2C device address (0x77) to communicate with.
###### Initialize BMP180
```c
bmp180_init(fd, &calib);
```
- Reads calibration constants from the sensor.
###### Read Temperature and Pressure
```c
bmp180_read_temperature(fd, &calib, &temperature);
bmp180_read_pressure(fd, &calib, &pressure);
```
- Uses previously stored calibration values to read and convert real temperature and pressure values.
###### Output in JSON Format
```c
printf("{\"temperature\": %.2f, \"pressure\": %.2f}\n", temperature, pressure);
```
- Very useful becouse we are integrating with a frontend (e.g. web UI or logger).
###### Cleanup
```c
close(fd);
```
- Closes the I2C device after finishing communication.
## Results
Photo to prove the functionality of the UI:
Screenshot of UI:
