PiSensor - Raspberry Pi Environmental Sensor Monitor

A C-based environmental monitoring system for Raspberry Pi that reads data from Si7021 (temperature/humidity) and CCS811 (eCO2/TVOC) sensors, providing both a command-line interface and HTTP server for data access.

Features

• Multi-sensor support: Reads from Si7021 (temperature & humidity) and CCS811 (eCO2 & TVOC) sensors
• HTTP API: Built-in web server providing sensor data in plain text format
• Command-line monitoring: Real-time sensor readings with customizable intervals
• Systemd integration: Can run as a system service
• Baseline management: CCS811 baseline calibration support
• Error handling: Robust sensor error detection and recovery
• Logging support: Optional CSV output for data logging

Hardware Requirements

• Raspberry Pi (any model with I2C support)
• Si7021 temperature/humidity sensor
• CCS811 air quality sensor (eCO2/TVOC)
• I2C connections between sensors and Raspberry Pi

Software Dependencies

Required Libraries

• wiringPi: GPIO and I2C library for Raspberry Pi
• GLib 2.40+: Core application framework
• libsoup 3.0+: HTTP server functionality
• autotools: Build system (autoconf, automake)

Installing Dependencies (Raspberry Pi OS)

# Update package list
sudo apt-get update

# Install build tools and dependencies
sudo apt-get install -y build-essential autoconf automake pkg-config
sudo apt-get install -y libglib2.0-dev libsoup-3.0-dev

# Install wiringPi
sudo apt-get install -y wiringpi

Building from Source

1. Clone or download the source code

2. Generate build configuration

   autoreconf --install

3. Configure the build

   ./configure

   Optional configuration flags:

   ./configure --with-service-user=pi --enable-warn-strict

4. Build the project

   make

5. Install (optional)

   sudo make install

Usage

HTTP Server Mode

Run the main sensor server:

./pisensor

The server will start on port 8080 and provide sensor data at:

• http://localhost:8080/reading - Returns plain text with all sensor readings

Example output:

72.50 F, 45.20 %, eCO2: 400 ppm, TVOC: 0 ppb

If the CCS811 sensor is warming up, you'll see:

72.50 F, 45.20 %, eCO2: 400 ppm, TVOC: 0 ppb (warming up: 5 min)

If there's an error reading sensors:

Error: latest Si7021 reading unavailable

Command-Line Monitor

Build and run the CLI monitor:

make
./monitor

Options:

• -i, --interval <seconds>: Set sampling interval (default: 5.0 seconds)
• -o, --output <file>: Log readings to CSV file
• -h, --help: Show help message

Examples:

# Basic monitoring
./monitor

# Custom interval and CSV logging
./monitor -i 10.0 -o sensor_data.csv

# Quick test with 2-second intervals
./monitor -i 2.0

Running as a Service

After installation, enable and start the systemd service:

sudo systemctl enable pisensor
sudo systemctl start pisensor
sudo systemctl status pisensor

View logs:

sudo journalctl -u pisensor -f

Configuration

Service User

By default, the service runs as the pi user. Change this during configuration:

./configure --with-service-user=youruser

Network Configuration

The HTTP server binds to all interfaces (0.0.0.0) on port 8080. To change this, modify the source code and rebuild.

Sensor Details

Si7021 (Temperature/Humidity)

• I2C Address: 0x40
• Temperature Range: -40°C to 125°C
• Humidity Range: 0-100% RH
• Accuracy: ±0.4°C, ±3% RH

CCS811 (Air Quality)

• I2C Address: 0x5A
• eCO2 Range: 400-8192 ppm
• TVOC Range: 0-1187 ppb
• Warm-up time: ~20 minutes for stable readings

Troubleshooting

Build Issues

Missing dependencies:

# Check for required packages
make check-deps

wiringPi not found:

# Install wiringPi
sudo apt-get install wiringpi
# OR build from source if needed

Runtime Issues

I2C not enabled:

# Enable I2C interface
sudo raspi-config
# Navigate to: Interface Options → I2C → Enable
sudo reboot

Permission denied:

# Add user to i2c group
sudo usermod -a -G i2c $USER
# Log out and back in

Sensor not detected:

# Check I2C devices
i2cdetect -y 1
# Should show 0x40 (Si7021) and 0x5A (CCS811)

CCS811 Issues

The CCS811 sensor requires a 20-minute warm-up period for accurate readings. The software includes automatic error recovery and baseline management.

Development

Project Structure

pisensor/
├── main.c              # HTTP server implementation
├── monitor.c           # Command-line monitor
├── configure.ac        # Autoconf configuration
├── Makefile.am         # Automake build rules
└── pisensor.service.in # Systemd service template

Build System

The project uses GNU Autotools:

• configure.ac: Defines build configuration and dependencies
• Makefile.am: Specifies build targets and installation rules

License

This project is licensed under the MIT License. See the LICENSE file for details.