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This project is based on ESP8266 modul, a cheap DHT22 sensor and a CO2 and VOC sensor that can be found on AliExpress! The sensor is the same that Elgato EVE Room (gen 1) has for indoor air quality monitoring!

Features:

• Indoor Air Quality Index
• Indoor CO2
• Indoor VOC density
• Indoor Temperature (only in 3rd party apps...thanks to Apple)
• Indoor Humidity
• Sensor Fault detection

Sensor properties:

The sensor based on technology called MEMS metal oxide sensor technology.

• It takes about 5 minutes for the sensor to heat up. Until that HomeKit will show Air quality is Unknown, VOC density and CO2 values will be 0! First functional reading after start up appears in at least 5 minutes. So keep in mind that it takes about 5 to 10 minutes for the sensor to work properly!

• The iAQ-Core sensor module is used to measure VOC levels and provide CO2 equivalent and TVOC equivalent predictions. The data is available via I2C bus. The sensor itself is protected by a plastic cap and a filter membrane, which should NOT be removed and touched.

• I2C bus SDA and SCL pins must be pulled up via 10K resistors according to iAQ Core C's datasheet! More about that in Hardware Setup!

• Other, cheaper sensors are on the market. One of these are CCS811 which comes from the same company that makes iAQ Core C. The CCS811 sensor wasn't that reliable, so i've decided to use iAQ Core C. This sensor works for me since 2016 and still reliable!

• The Air Quality Index calculating is implemented from Elgato EVE Room which using the same iAQ Core sensor for indoor air quality monitoring, so i've used this as reference to calculate IAQ index!

Air Quality Index:

• From 450ppm to 700ppm HomeKit shows that air quality is Excellent
• From 700ppm to 1100ppm Good
• From 1100ppm to 1600ppm Fair
• From 1600ppm to 2100ppm Inferior
• Above 2100ppm air quality is Poor
• Under 450ppm is Unknown

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