Finding a comprehensive DIY air quality sensor kit that measures both CO2 and PM2.5, integrates seamlessly with Home Assistant, and supports Zigbee, all while staying under $100, presents a challenge, but several viable options exist. The key is to balance cost, accuracy, and ease of integration. While a single, off-the-shelf solution meeting all criteria perfectly is rare, combining DIY components or making strategic choices among available products can achieve the desired result.

Understanding the Sensor Landscape

Before diving into specific recommendations, it's important to understand the different types of sensors and their limitations. CO2 sensors typically use Non-Dispersive Infrared (NDIR) technology, which is more accurate but also more expensive. Cheaper alternatives often rely on volatile organic compound (VOC) sensors, which provide an estimate of CO2 levels but are less precise. PM2.5 sensors, on the other hand, use laser scattering or other optical methods to measure the concentration of fine particulate matter. Understanding these differences will help you make informed decisions.

DIY Options: Building Your Own Sensor

For those comfortable with a bit of DIY, building your own sensor offers the most flexibility and cost control. Here's a breakdown of the components and considerations:

CO2 Sensor

The SenseAir S8 LP is a highly recommended NDIR CO2 sensor known for its accuracy and reliability. It typically costs around $30. While there are cheaper options, the S8 LP provides the most accurate readings for the price. It's crucial to use a true NDIR sensor for reliable CO2 measurements, as VOC-based sensors are not as accurate for CO2 specifically.

PM2.5 Sensor

For PM2.5 measurements, the Plantower PMS5003 or PMS7003 are industry-standard laser particle sensors. These sensors are known for their high accuracy and ease of interfacing. They typically cost around $20. These sensors are widely used and well-supported, making them a reliable choice for DIY projects.

Microcontroller and Zigbee Module

To process the sensor data and communicate with Home Assistant, you'll need a microcontroller and a Zigbee module. The ESP32 or ESP8266 are popular choices for microcontrollers, costing around $5. For Zigbee connectivity, the CC2530 module is a well-supported and affordable option, typically costing between $5 and $10. These components are readily available and have extensive community support, making integration easier.

Total DIY Cost

With the components listed above, the total cost for a DIY sensor kit should fall between $50 and $70, excluding basic components like wires, a case, and a power supply. This is well within the $100 budget and provides a highly customizable and accurate solution.

DIY Integration with Home Assistant

Integrating a DIY sensor with Home Assistant requires some technical knowledge. You'll need to write code to read the sensor data, format it, and send it to Home Assistant via Zigbee. This can be done using custom firmware like Zigbee2MQTT, which provides a bridge between Zigbee devices and Home Assistant. Alternatively, you can use the ESPHome firmware for the ESP32/ESP8266, which simplifies the integration process. ESPHome allows you to define the sensors, their data formats, and how they connect to Home Assistant, all through a configuration file. This approach is often preferred for its ease of use and flexibility.

Ready-Made Options: Balancing Cost and Convenience

While DIY offers the most flexibility, several ready-made options can also meet your needs, though they may require some compromises or additional integration steps. Here are some of the most relevant options:

AirGradient ONE DIY Kit

The AirGradient ONE DIY Kit is a comprehensive option that includes an ESP8266, an OLED display, an SHT30 temperature/humidity sensor, a PMS5003 PM2.5 sensor, and a SenseAir S8 CO2 sensor. While the kit itself costs around $130, it provides a complete solution with all necessary components. Although it doesn't have native Zigbee support, it can be integrated with Home Assistant using custom drivers or by configuring it as a Bluetooth proxy. This kit is a good option if you prefer a more structured approach and are willing to invest a bit more for a complete package.

Ecowitt WH45 Air Quality Sensor

The Ecowitt WH45 is another option that measures CO2, humidity, PM2.5, and PM10. The indoor sensor costs around $170, and the gateway costs an additional $34. While this is over the $100 budget, it offers a robust solution with multiple sensor types and integration capabilities with Hubitat, which can then be connected to Home Assistant. This option is suitable if you need a pre-built solution with a wide range of sensors and are willing to invest more.

Xiaomi Mijia CO2 Monitor

The Xiaomi Mijia CO2 Monitor is a standalone device that measures CO2, temperature, and humidity. It supports Zigbee and can be integrated with Home Assistant through the Zigbee2MQTT add-on. It typically costs between $60 and $80. This is a good option if you are primarily focused on CO2 monitoring and want a ready-made device that integrates easily with Home Assistant.

Xiaomi Aqara Air Quality Monitor

The Xiaomi Aqara Air Quality Monitor measures CO2, TVOC, temperature, and humidity. It also supports Zigbee and can be integrated with Home Assistant via Zigbee2MQTT. It costs around $70-$90. This is a good option if you want a comprehensive sensor that measures multiple parameters and integrates well with Home Assistant.

Tuya Smart Air Quality Sensor

The Tuya Smart Air Quality Sensor measures CO2, PM2.5, humidity, and temperature. It supports Zigbee and can be integrated with Tuya-based Zigbee hubs. The price varies but is generally under $100. This is a budget-friendly option that provides a good range of measurements, but it may require more setup compared to more well-known brands.

IKEA VINDRIKTNING

The IKEA VINDRIKTNING is a very affordable PM2.5 sensor, costing around $15. While it doesn't measure CO2 and doesn't have native Zigbee support, it can be modified to add Zigbee functionality. This is a good option if you are on a very tight budget and only need PM2.5 monitoring, and are comfortable with some modifications.

Zigbee Integration with Home Assistant

Regardless of whether you choose a DIY or ready-made option, you'll need a Zigbee gateway to connect your sensors to Home Assistant. Popular options include the Zigbee2MQTT with a compatible USB stick or the ConBee II. Zigbee2MQTT is a popular choice for its flexibility and support for a wide range of devices. It acts as a bridge between your Zigbee devices and Home Assistant, allowing you to control and monitor your sensors through the Home Assistant interface. The ConBee II is another reliable option that provides a stable Zigbee connection.

Recommendations

Based on the available options, here are some recommendations:

Best Overall DIY Option

For the best balance of cost, accuracy, and flexibility, the DIY approach using the SenseAir S8 LP for CO2, the Plantower PMS5003/7003 for PM2.5, and an ESP32/ESP8266 with a CC2530 Zigbee module is highly recommended. This combination provides accurate measurements and allows for full customization and integration with Home Assistant using Zigbee2MQTT or ESPHome. The total cost should be well under $100.

Best Ready-Made Option for CO2 and PM2.5

If you prefer a ready-made solution, the Xiaomi Aqara Air Quality Monitor is a good choice, as it measures both CO2 and PM2.5, along with other parameters, and integrates well with Home Assistant via Zigbee2MQTT. However, it is slightly more expensive than the DIY option.

Best Budget Option for PM2.5

If you are primarily concerned with PM2.5 and are on a very tight budget, the IKEA VINDRIKTNING, with modifications to add Zigbee support, is a viable option. However, it does not measure CO2.

Best Budget Option for CO2

If you are primarily concerned with CO2 and are on a tight budget, the Xiaomi Mijia CO2 Monitor is a good choice, as it provides accurate CO2 measurements and integrates well with Home Assistant via Zigbee2MQTT.

Additional Considerations

• Calibration: Ensure you follow the manufacturer's guidelines for sensor calibration to ensure accurate readings. Some sensors may require periodic calibration.

• Power Supply: Consider how you will power your sensor. USB power is a common option for DIY projects.

• Enclosure: Choose a suitable enclosure to protect your sensor from dust and other environmental factors.

• Firmware Updates: Keep your firmware up to date to ensure optimal performance and security.

Conclusion

Finding a comprehensive CO2 and PM2.5 sensor kit under $100 with Zigbee support for Home Assistant requires careful consideration of your needs and technical skills. While a single, perfect off-the-shelf solution is difficult to find, combining DIY components or making strategic choices among available products can achieve the desired result. The DIY approach offers the most flexibility and cost control, while ready-made options provide convenience and ease of use. By carefully evaluating your options and considering the recommendations above, you can create a reliable and effective air quality monitoring system for your home.