Indoor Air Quality Combo Sensor - SCD41/SEN55 (Qwiic)

Jargon buster

Plain-language definitions for the technical terms used above.

AP3012

AP3012 is the part number of a step-up (boost) DC/DC converter chip, which raises a lower input voltage to a higher output voltage. The part number matters if you need to check its power limits, switching frequency, or other datasheet details.

Automatic Self-Calibration

Automatic Self-Calibration is a built-in routine that adjusts the sensor over time to reduce drift in its readings. It matters for long-running indoor monitors because it can help keep measurements stable without frequent manual calibration.

boost converter

A boost converter is a switching power circuit that raises a lower input voltage to a higher output voltage. It is used when a device needs more voltage than its power source provides, for example running a 5 V sensor from a 3.3 V supply.

CMOSens

CMOSens is Sensirion’s integrated sensor technology that combines sensing elements and electronics in one package. It matters because it affects how the sensor measures temperature and humidity and how it is supported by the manufacturer’s libraries and datasheets.

DC

DC means direct current, where electricity flows in one constant direction, as supplied by batteries, USB ports and many plug-pack power supplies. When a product specifies DC, it runs from a DC supply rather than mains AC, so you need to provide the correct voltage and polarity.

I2C

I2C is a two-wire communication bus used by many sensors and small modules. It matters because several I2C devices can share the same two wires, but each device needs a compatible address and your controller must support I2C.

I2C address

An I2C address is the number a device uses so a microcontroller can tell it apart from other devices on the same I2C bus. It matters because two devices with the same fixed address may conflict if used together.

Matter

A smart home connectivity standard designed to let devices work across different ecosystems. It matters if you want a project to integrate more easily with platforms such as Apple Home, Google Home, or other Matter-compatible systems.

NOx

NOx means nitrogen oxides, a group of gases often linked to combustion sources such as gas stoves, heaters, and vehicle exhaust. A NOx index can help show changes in indoor air quality, especially where combustion or outdoor pollution may affect the room.

particulate matter

Particulate matter means tiny particles suspended in the air, such as dust, smoke, pollen, or pollution. A sensor that measures it is useful for air-quality projects because particle levels can affect comfort and health.

PASens

PASens is Sensirion’s name for its photoacoustic sensing technology used in some CO2 sensors. Knowing this helps explain why the sensor uses light and a microphone internally rather than a simple chemical gas sensor.

photoacoustic measurement

Photoacoustic measurement detects gas by shining light into a sample and listening for tiny pressure waves created when the gas absorbs that light. In a CO2 sensor, this matters because it is the method used to estimate carbon dioxide concentration.

PM1.0

PM1.0 refers to airborne particles with a diameter of about 1 micrometre or smaller. This size category matters because smaller particles can stay airborne longer and may come from sources such as smoke or combustion.

PM10

PM10 refers to airborne particles with a diameter of about 10 micrometres or smaller. It includes larger dust and pollen-like particles, so it is useful for detecting coarser airborne pollution.

PM2.5

PM2.5 refers to airborne particles with a diameter of about 2.5 micrometres or smaller. It is a common air-quality measurement because these fine particles can be breathed deep into the lungs.

PM4

PM4 refers to airborne particles with a diameter of about 4 micrometres or smaller. It gives another particle-size category, which can help compare different dust, smoke, or indoor pollution sources.

ppm

ppm means parts per million, a common way to express very small gas concentrations in air. For CO₂ sensors, the ppm range tells you what levels the sensor can measure, such as normal indoor air through to poorly ventilated spaces.

PTH

Plated through-hole means the pin holes are metal-lined so solder connects the pad on both sides of the board. It is useful for connectors and headers that need a strong mechanical and electrical connection.

Qwiic

Qwiic is a plug-in connector system for I2C devices that uses small 4-pin cables, so you can connect compatible sensors without soldering. It matters because your controller or adapter also needs Qwiic, or you will need a cable or breakout to wire it up.

SCD41

A Sensirion sensor module that measures carbon dioxide, temperature, and humidity. The part number matters because library support, I2C address, accuracy, power use, and measurement range are specific to this sensor.

SEN55

SEN55 is a Sensirion environmental sensor module that combines several measurements in one package: particulate matter, a VOC air-quality index, a NOx air-quality index, temperature and humidity. The part number matters because it tells you which air-quality readings the module can report, and its library support, I2C interface and specifications are specific to this part.

VOC

Volatile organic compounds are gases released from things like paints, cleaners, smoke, and some plastics. A VOC reading helps indicate indoor air quality, but it is usually an index or estimate rather than a direct identification of each chemical.