Hardware Overview
Let's take a closer look at the pair of sensors along with other hardware present on this Qwiic sensor breakout.
SEN55 Particle, VOC, Humidity, and Temperature Sensor
The SEN55 Particle and VOC sensor module measures particulate matter and volatile organic compounds (VOCs) along with humidity and temperature. The SEN55 is designed with the idea to be a simple plug-and-play solution and includes all sensors, processors, power control, and fan inside a compact housing all with a single, calibrated, digital signal output communicating over I2C making it perfect to integrate into this Qwiic combination breakout.
The SEN55 reports measurments of particulate matter, VOC index, NOx indect, temperature, and relative humidity every second. The sensor measures particulates of the following size specifications: PM1, PM2.5, PM4, and PM10 from a concentration of 0 to 1,000 µg/m3. It also senses both VOC and NOx indexes from 1 to 500 index points. Lastly, it measures temperature from 15 to 30°C and relative humidity from 30 to 70%RH. It offers a robust set of control registers to take and report measurements as well as check the status of the module and its components. The table below outlines some of the sensing parameters for the SEN55. Refer to the datasheet for a complete overview.
| Parameter | Units | Min | Typ | Max | Conditions/Notes | |
|---|---|---|---|---|---|---|
| Mass concentration range | µg/m3 | - | 0 | - | 1,000 | - |
| PM1.0 Mass concentration size | µg | 0.3 | - | 1.0 | - | |
| PM2.5 Mass concentration size | µg | 0.3 | - | 2.5 | - | |
| PM4 Mass concentration size | µg | 0.3 | - | 4.0 | - | |
| PM10 Mass concentration size | µg | 0.3 | - | 10.0 | - | |
| Temperature accuracy (Typ.) | °C | - | ±0.45 | - | @ 15-30 °C, 50 %RH | |
| Temperature repeatability | °C | - | 0.1 | - | @25°C, 50 %RH | |
| Relative humidity accuracy (Typ.) | %RH | - | ±4.5 | - | @25°C, 30-70 %RH | |
| Relative humidity repeatability | %RH | - | ±1 | - | @25°C, 50 %RH | |
| VOC Index output | VOC Index points | 1 | - | 500 | - | |
| VOC Index repeatability | VOC Index points | - | <±5 | - | - | |
| NOx Index output | NOx Index points | 1 | - | 500 | - | |
| NOx Index repeatability | NOx Index points | - | <±10 | - | - |
SEN55 Power
The SEN55 accepts a supply voltage between 4.5V to 5.5V with a typical voltage of 5V with a peak current draw of 110mA@5V. The SparkFun Indoor Air Quality Sensor uses an on-board buck/boost circuit to boost the 3.3V from a Qwiic connector or to the 3.3V PTH pin to 5V.
SCD41 CO2 Humidity and Temperature Sensor
The SCD41 CO2 sensor uses Sensirion's PASense™, a photoacoustic measurement system, to accurately measure CO2 concentration using a combination of a narrow band of IR light and a microphone. The sensor also has a built-in humidity and temperatuer sensor using Sensirion's CMOSens™ technology to provide environmental data and compensate for environmental conditions in CO2 measurement. For a detailed overview of the SCD41 sensor, refer to the datasheet.
Now you may be curious as to just what photoacoustic measuring actually is. Photoacoustic measuring uses light (photo) and sound/vibrations (acoustic) in tandem to measure the the photoacoustic effect when energy is absorbed by particles (in the case of these sensors, CO2 molecules). The SCD41 has an IR emitter with a filter to shine a specific IR light into the sensing area. CO2 molecules inside the sensing area absorb energy from the emitted IR light and vibrate. The microphone inside the sensing area picks up this acoustic vibration and then this data is processed to report CO2 concentration. This is just a quick and basic explanation of the photoacoustic process used in this sensor. For detailed information on Sensirion's PASens and CMOSens technology, refer to their technology page.
| Parameter | Units | Min | Typ | Max | Notes |
|---|---|---|---|---|---|
| CO2 Output Range | ppm | 0 | - | 40,000 | |
| CO2 Measurement Accuracy | ppm | - | ±(40 + 5%) | - | - |
| Humidity Range | %RH | 0 | - | 100 | |
| Humidity Accuracy | %RH | - | ±6 | - | 15°C - 35°C, 20%RH - 65%RH |
| - | ±9 | - | -10°C - 60 °C, 0%RH - 100%RH | ||
| Temperature Range | °C | -10 | - | 60 | |
| Temperature Accuracy | °C | - | ±0.8 | - | 15°C - 35°C |
| - | ±1.5 | - | -10°C - 60°C |
Qwiic & I2C Interface
The Indoor Air Quality Sensor operates over I2C using either the two Qwiic connectors or the 0.1"-spaced plated through-hole (PTH) header. Power for the board is supplied over either of these options as well.
Power LED
There is just one red LED on the board to indicate power. By default, it is always powered whenever 3.3V is present though users can disable it by adjusting the solder jumper covered in the next section.
Solder Jumpers
The board has two solder jumpers labeled PWR and I2C. The PWR jumper completes the power LED circuit and is CLOSED by default. Open the jumper to disable the power LED. The I2C jumper pulls the I2C SDA and SCL lines to 3.3V via a pair of 2.2kΩ resistors. This three way jumper is completely closed by default. Open it completely to disable the pullup resistors.
Board Dimensions
This Qwiic breakout runs a bit larger than standard Qwiic breakouts to fit the SEN55 and measures 3.25" x 1.75" (82.55mm x 44.45mm) and has four mounting holes that fit a 4-40 screw. The SEN55 is a bit of an odd shape to fit everything in the housing but it measures 0.878" (22.3mm) at it's tallest and it's footprint is 2.06" x 1.70" (52.3 mm x 43.3 mm). For detailed measurements of the entire sensor package, refer to the SEN55 datasheet.
