i have two SCD41 from AliExpress, probably used before, idk.
Both have absolutely the same behavior. Repeatability is +-40 even in perfectly stable (inside box) conditions.
I did forcefully calibrate them, reboot, set the altitude etc. Tried different measurement command - result is the same. I am using official lib with ESP8266.
is it poor quality sensor or am i doing smth wrong?
From AliExpress, who knows what you get?
For sensors like that, I think it is worthwhile to buy from a reputable seller like Adafruit, who support their products with excellent instructional materials, a professionally staffed forum, and replace faulty units.
So, it's not how it should behave?
What does the data sheet tell you? You might go through Adafruit's guide and compare results.
put a capacitor 0.1uF = 104 capacitor, One end to the pin and the other to GND (and leave everything else the same).
Maybe it is just this.
Thank you, I'll try! Although I didn't know I need to from datasheet....
I read it. I did compare results with utube videos, where reputability was +- 5, not 40
Again, who knows? You might have received counterfeit sensors, factory rejects, etc.
The measurement noise is one issue, but that can be reduced by averaging. The more important issue is whether the readings mean anything. The only way to determine that is to measure gas mixtures with known CO2 concentrations, or compare results with those from a commercial, calibrated and certified CO2 sensor.
Yeah, the reading are correct.
I have another CO2 monitor to compare.
Also thought about averaging data....
If you are happy that the readings are basically accurate, then I don't see a big problem.
For random measurement noise, the standard deviation of the measurements is reduced by sqrt(N), averaging N measurements.
Without averaging it is problem...
Cause right now is 560... If it's highest value - it could be 480... If it lowest it could be 640...
480-640 accuracy isn't dreaming))
Also the esp8266 has a lot of sensors and work to do... I can't just ask CO2 non stop...
Evidently you are not happy with the results. In that case, I stick with my original recommendation to buy the genuine item from a reputable supplier, like Adafruit.
I have no affiliation with Adafruit, but they have treated me fairly and professionally in the very few cases where problems came up.
As far as I read about it:
there's no other scd41 sensors, only original.
In China they are reassemble it from used items and sold it again.
Is it's true - it's hard to believe that I bought two sensors with exactly the same issue. I believe that only if those sensors have this issue frequently.
sadly, 104 capacitor did nothing :')
This might be true. What about the sensor board? Or someone selling sensors that didn't pass quality control..
I have doubts that Sensirion is selling sensors that perform out of specs.
Anyway in your serial monitor image there is not that much fluctuation.
Also, try with another power source.
Thank you for suggestions! i tried both pc power end external - same...
Also i found resolution) i will post it in few minutes separated!
So, at first i gotta say that both sensors is working...
The short answer is - i use "Periodic Measurement" instead of "Single Shot Measurement".
The long answer:
First of all, i tried all three Measurement at the beginning and result was the same... Or maybe in a rush i didn't wait few minutes for measurements to settle down a bit, i don't know...
Another thought that i have - initially i used "Periodic Measurement", than i tried, "ECO Periodic Measurement", then switched to "Single Shot Measurement"... And after i tried "Forced Recalibration" function...
After that i never tried to switch back to "Periodic Measurement" till today...
So my though is that it never worked correctly with Single Shot, but Recalibration fixed "Periodic Measurement"...
update "low_power_periodic_measurement" also working correctly...
Makes sense, nice that you resolved.
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