Pico SCD30 Access Point

This repository contains a C-based project for the Raspberry Pi Pico W that transforms the device into a standalone Wi-Fi Access Point and Web Server to monitor CO2, temperature, and humidity using a Sensirion SCD30 sensor.

Screenshot

Features

• Standalone Access Point: Hosts a Wi-Fi network named Pico_CO2_Monitor.
• Web Dashboard: Serves a mobile-friendly HTML interface that auto-refreshes every 3 seconds to display real-time sensor data.
• Integrated Network Services: Includes a built-in DHCP server and DNS server to provide a seamless "captive portal-like" experience.
• Thread-Safe Networking: Utilizes pico_cyw43_arch_lwip_threadsafe_background for stable Wi-Fi and sensor concurrent operations.
• Robust Sensor Handling: Implements a blocking read with retries to mitigate I2C collisions during Wi-Fi activity.

Hardware Requirements

• Raspberry Pi Pico W or Pico 2 W.
• Sensirion SCD30 Sensor.

Wiring:

SCD30 Pin	Pico W Pin
VCC	3V3 / VSYS
GND	GND
SDA	GPIO 4
SCL	GPIO 5

Repository Structure

• main.c: Core application logic, Web Server, and sensor polling loop.
• dhcpserver/: Implementation of a lightweight DHCP server for assigning client IPs.
• dnsserver/: A simple DNS server that resolves all queries to the Pico's IP (192.168.4.1).
• sensirion_i2c_hal.c: Hardware Abstraction Layer mapping Sensirion's I2C calls to the Pico SDK.
  • Can configure I2C pins and speed via sensirion_i2c_hal_init().
• lwipopts.h: Optimized LwIP configuration for Access Point and DHCP functionality.

Build and Flash

1. Use VSCode with the official Pico extension for easier building and flashing.
2. Ctlr+Shift+P -> CMake: Configure
3. Click Compile in bottom bar.
4. Put your Pico W into BOOTSEL mode (hold the BOOTSEL button while plugging it in).
5. Click Run in bottom bar to flash the firmware.

Usage

1. Power the Pico W.
2. Connect your phone or computer to the Wi-Fi network "Pico_CO2_Monitor" using the password "12345678".
3. Open a web browser and navigate to http://192.168.4.1.
4. The dashboard will display current CO2 (ppm), Temperature (°C), and Humidity (%).

Notes

• The SCD30 sensor is set to a 2-second measurement interval to balance responsiveness and I2C stability.
• The web page auto-refreshes every 3 seconds to provide near real-time updates without overwhelming the network or sensor.
• The I2C bus rate was set to 50kHz which seems to prevent the senor from locking up.
• Probably should not add more sensors to the same I2C bus.

License

This project is licensed under the MIT License - see the LICENSE file for details

Acknowledgments

• picow_access_point example
• Sensirion Embedded I2C SCD30 Driver