Testing and hacking the SCD 41

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<< CO2 Soil Respiration Chamber#UROŠ new CO2 soil chambers

Sensirion webScreenshot.jpg

Circuit Python and FeatherS2

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With all the libraries and examples prepared by sensirion and Adafruit, it was easy to connect it all together using the FeatherS2 and CircuitPython. A first prototype is connected and working.

RandePrototype SCD41 indoorTest.jpg

First measurements look promising, very stable, relatively fast response times. The library is very easy to use, auto-calibration has to be turned off. During the start of the code you can adjust a temperature_offset to calibrate the temp sensor. Additionally you have to adjust the pressure or altitude to where you are doing the measurement, altitude offset (default hardware is 0m). First experiments show that this is pretty crucial, details will have to explored and discussed with the sensirion tech team.

Serial Plotter and how to get dedicated soil resp data

Started to use this tool tauno-serial-plotter to plot data and export .png or .csv for further analysis / storage.

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Testing and hacking the SCD 41

Checking the PCB and the footprint to plan our own reflowing of PCB

Opening up the sensor

What is inside? As described on the sensirion product page, the new sensor works on the "photo-accoustic effect". So it's similar, but also a different method, than other NDIR sensors.

It's pretty easy to understand what's under the hood for the SCD41. There is a signal-processor, to read and control the sensor components and communicate to the outside via I2C, there is the "classic" SH40 temperature & humidity sensor, and now... There is an IR emmiter with a dedicted filter on it and a MEMS microphone. Everything is enclosed within a small metal case, with a hole to the outside world and a particle filter stuck onto it.

Photoacoustic effect is the generation of acoustic waves as a result of light absorption in a material. As an example, consider a laser beam that is passed through a gas sample, which is enclosed in a cell of a constant volume. The laser energy absorbed by the sample molecules leads to local heating of the gas, which causes a pressure increase. If the optical excitation of molecules is done periodically, by modulating the laser power or frequency, also the pressure change is periodic. This acoustic wave at the modulation frequency can be detected with a microphone. The microphone signal is directly proportional to the absorbed power, which makes it possible to determine the concentration of absorbing molecules in the sample. Taken from this source on laser spectroscopy

Desing UROŠ - CO2 brkout PCB

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PCB (printed circuit board) breakout board for CO2 sensor (SCD41), NEO-pixel (WS2812B) and I2C interface (JST-SH4)

Designed with open source software: Kicad, Inkscape and svg2shenzhen

The files "as ordered" are available on github: https://github.com/GenericLab/UROS-CO2_brkout

It arrived!!!

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Minting UROŠ - CO2 brkout as NFT on OpenSea

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Go to OpenSea NFT marketplace