MH-Z14A CO2 sensor
-
@korttoma
Where is the preheat logic in your sketch?Values in the preheat time could be wrong....
@FotoFieber Yeah, I don't have preheat logic but that would only account for values when I first plug it in. I get the strange values even if it has been running for weeks. I will try to get a graph of what I see this evening so you can see what I mean. I'm seriously considering to just exclude the value 562 from being sent to the controller.
- Tomas
-
@FotoFieber Yeah, I don't have preheat logic but that would only account for values when I first plug it in. I get the strange values even if it has been running for weeks. I will try to get a graph of what I see this evening so you can see what I mean. I'm seriously considering to just exclude the value 562 from being sent to the controller.
@korttoma Sounds like you have a faulty sensor. Did you try analogue output? This is just to make sure the sensor is working.
There are PWM or UART.
Did you try both of them? I am using 5V Arduino Nano with no problem.The digital pins communicate via PWM or UART. Output (and input for UART) of these ports work on 3.3 Volts - this means you should change the ARef of your Arduino - or rescale your values -
-
@korttoma try to put it outside for some time to recalibrate. If it does not help, you may need to calibrate it.
Or you just got a bad one.
@alexsh1 Will the sensor really recalibrate by itself if I put it outside?
I could send a "zero calibration" command via serial but then I would need to "input Nitrogen gas for 5 minutes when make zero calibration. "
Instead of exposing it to nitrogen gas could I just like you said put it outside and then send the "zero calibration" command?
To do the " span calibration" I would need to know what kind of values to send to it and I have no idea.
btw, here are some values I read now via serial at the office (I do not get the 562 value so far) but does these values seem reasonable for a well ventilated office?
HiResp :3 LoResp :-21 Tem.channel :63 c02ppm :747 HiResp :3 LoResp :124 Tem.channel :63 c02ppm :892 HiResp :3 LoResp :21 Tem.channel :63 c02ppm :789 HiResp :2 LoResp :-57 Tem.channel :63 c02ppm :455 HiResp :2 LoResp :-110 Tem.channel :63 c02ppm :402 HiResp :2 LoResp :99 Tem.channel :63 c02ppm :611 HiResp :2 LoResp :51 Tem.channel :63 c02ppm :563 HiResp :2 LoResp :20 Tem.channel :63 c02ppm :532 HiResp :1 LoResp :-2 Tem.channel :63 c02ppm :254 HiResp :1 LoResp :-32 Tem.channel :63 c02ppm :224 HiResp :1 LoResp :-55 Tem.channel :63 c02ppm :201 HiResp :1 LoResp :-68 Tem.channel :63 c02ppm :188 HiResp :1 LoResp :-75 Tem.channel :63 c02ppm :181 HiResp :1 LoResp :-79 Tem.channel :63 c02ppm :177 HiResp :1 LoResp :-98 Tem.channel :63 c02ppm :158 HiResp :1 LoResp :-102 Tem.channel :63 c02ppm :154 HiResp :1 LoResp :-109 Tem.channel :63 c02ppm :147 HiResp :1 LoResp :-116 Tem.channel :63 c02ppm :140 HiResp :1 LoResp :-125 Tem.channel :63 c02ppm :131 HiResp :1 LoResp :-124 Tem.channel :63 c02ppm :132 HiResp :1 LoResp :111 Tem.channel :63 c02ppm :367 HiResp :1 LoResp :115 Tem.channel :63 c02ppm :371 HiResp :1 LoResp :121 Tem.channel :63 c02ppm :377 HiResp :1 LoResp :114 Tem.channel :63 c02ppm :370 HiResp :1 LoResp :-62 Tem.channel :63 c02ppm :194 HiResp :1 LoResp :-7 Tem.channel :63 c02ppm :249 HiResp :1 LoResp :-53 Tem.channel :63 c02ppm :203 HiResp :1 LoResp :-68 Tem.channel :63 c02ppm :188 HiResp :1 LoResp :-96 Tem.channel :63 c02ppm :160 HiResp :1 LoResp :-111 Tem.channel :63 c02ppm :145 HiResp :1 LoResp :-121 Tem.channel :63 c02ppm :135 HiResp :1 LoResp :-127 Tem.channel :63 c02ppm :129 HiResp :1 LoResp :-124 Tem.channel :63 c02ppm :132 HiResp :1 LoResp :-126 Tem.channel :63 c02ppm :130 HiResp :1 LoResp :-126 Tem.channel :63 c02ppm :130 HiResp :1 LoResp :-110 Tem.channel :63 c02ppm :146 HiResp :1 LoResp :-110 Tem.channel :63 c02ppm :146 HiResp :1 LoResp :-60 Tem.channel :63 c02ppm :196 HiResp :1 LoResp :-69 Tem.channel :63 c02ppm :187 HiResp :1 LoResp :-101 Tem.channel :63 c02ppm :155 HiResp :1 LoResp :-104 Tem.channel :63 c02ppm :152 HiResp :1 LoResp :-114 Tem.channel :63 c02ppm :142 HiResp :1 LoResp :-128 Tem.channel :63 c02ppm :128 HiResp :1 LoResp :-122 Tem.channel :63 c02ppm :134 HiResp :1 LoResp :122 Tem.channel :63 c02ppm :378 HiResp :1 LoResp :119 Tem.channel :63 c02ppm :375 HiResp :1 LoResp :-128 Tem.channel :63 c02ppm :128 HiResp :1 LoResp :-86 Tem.channel :63 c02ppm :170 HiResp :1 LoResp :-110 Tem.channel :63 c02ppm :146 HiResp :1 LoResp :-123 Tem.channel :63 c02ppm :133 HiResp :1 LoResp :-101 Tem.channel :63 c02ppm :155 HiResp :1 LoResp :-75 Tem.channel :63 c02ppm :181 HiResp :1 LoResp :-92 Tem.channel :63 c02ppm :164 HiResp :1 LoResp :-101 Tem.channel :63 c02ppm :155 HiResp :1 LoResp :-123 Tem.channel :63 c02ppm :133 HiResp :1 LoResp :-114 Tem.channel :63 c02ppm :142 HiResp :1 LoResp :-127 Tem.channel :63 c02ppm :129 HiResp :1 LoResp :-120 Tem.channel :63 c02ppm :136 HiResp :1 LoResp :126 Tem.channel :63 c02ppm :382 HiResp :1 LoResp :118 Tem.channel :63 c02ppm :374 HiResp :1 LoResp :-127 Tem.channel :63 c02ppm :129 HiResp :1 LoResp :118 Tem.channel :63 c02ppm :374 HiResp :1 LoResp :120 Tem.channel :63 c02ppm :376 HiResp :1 LoResp :118 Tem.channel :63 c02ppm :374 HiResp :1 LoResp :115 Tem.channel :63 c02ppm :371 HiResp :1 LoResp :124 Tem.channel :63 c02ppm :380 HiResp :1 LoResp :120 Tem.channel :63 c02ppm :376 HiResp :1 LoResp :-119 Tem.channel :63 c02ppm :137 HiResp :1 LoResp :-126 Tem.channel :63 c02ppm :130 HiResp :1 LoResp :-127 Tem.channel :63 c02ppm :129 HiResp :1 LoResp :-124 Tem.channel :63 c02ppm :132 HiResp :1 LoResp :121 Tem.channel :63 c02ppm :377 HiResp :1 LoResp :114 Tem.channel :63 c02ppm :370 HiResp :1 LoResp :108 Tem.channel :63 c02ppm :364 HiResp :1 LoResp :108 Tem.channel :63 c02ppm :364 HiResp :1 LoResp :119 Tem.channel :63 c02ppm :375 HiResp :1 LoResp :-110 Tem.channel :63 c02ppm :146 HiResp :1 LoResp :124 Tem.channel :63 c02ppm :380 HiResp :1 LoResp :127 Tem.channel :63 c02ppm :383 HiResp :1 LoResp :-43 Tem.channel :63 c02ppm :213 HiResp :1 LoResp :-72 Tem.channel :63 c02ppm :184 HiResp :1 LoResp :-77 Tem.channel :63 c02ppm :179 HiResp :1 LoResp :-63 Tem.channel :63 c02ppm :193 HiResp :1 LoResp :-92 Tem.channel :63 c02ppm :164 HiResp :1 LoResp :-105 Tem.channel :63 c02ppm :151 HiResp :1 LoResp :-116 Tem.channel :63 c02ppm :140 HiResp :2 LoResp :41 Tem.channel :63 c02ppm :553 HiResp :2 LoResp :47 Tem.channel :63 c02ppm :559 HiResp :2 LoResp :26 Tem.channel :63 c02ppm :538 HiResp :2 LoResp :-107 Tem.channel :63 c02ppm :405 HiResp :2 LoResp :-76 Tem.channel :63 c02ppm :436 HiResp :2 LoResp :-97 Tem.channel :63 c02ppm :415 HiResp :2 LoResp :-109 Tem.channel :63 c02ppm :403 HiResp :2 LoResp :106 Tem.channel :63 c02ppm :618 HiResp :2 LoResp :-96 Tem.channel :63 c02ppm :416 HiResp :2 LoResp :80 Tem.channel :63 c02ppm :592 HiResp :2 LoResp :69 Tem.channel :63 c02ppm :581 HiResp :2 LoResp :40 Tem.channel :63 c02ppm :552 HiResp :2 LoResp :84 Tem.channel :63 c02ppm :596 HiResp :2 LoResp :45 Tem.channel :63 c02ppm :557 HiResp :2 LoResp :3 Tem.channel :63 c02ppm :515 HiResp :1 LoResp :-30 Tem.channel :63 c02ppm :226 HiResp :1 LoResp :-62 Tem.channel :63 c02ppm :194 HiResp :1 LoResp :-73 Tem.channel :63 c02ppm :183 HiResp :1 LoResp :-75 Tem.channel :63 c02ppm :181 HiResp :1 LoResp :-96 Tem.channel :63 c02ppm :160 HiResp :1 LoResp :-89 Tem.channel :63 c02ppm :167 HiResp :1 LoResp :-101 Tem.channel :63 c02ppm :155 HiResp :1 LoResp :-112 Tem.channel :63 c02ppm :144 HiResp :1 LoResp :-107 Tem.channel :63 c02ppm :149 HiResp :1 LoResp :-112 Tem.channel :63 c02ppm :144 HiResp :1 LoResp :-110 Tem.channel :63 c02ppm :146 HiResp :1 LoResp :-124 Tem.channel :63 c02ppm :132 HiResp :1 LoResp :-120 Tem.channel :63 c02ppm :136 HiResp :1 LoResp :-75 Tem.channel :63 c02ppm :181Some of the values seem a bit low to me. Especially while the HiResp is 1 or the LoResp is negative.
I will do this test again at home when I get the chance.
-
@korttoma
In the technical specification I only find the calibration with nitrogen. I don't think, that putting it outside, will help, as it is usually at around 400 ppm at the moment. (AFAIK netatmo sets the lowest measured value in the last one or two weeks to 400 for calibration). -
@korttoma values are completely off. Co2 cannot go down below 300 level. This is a value of co2 outside (300-400).
You have to calibrate it regularly. Zero calibration (this is what you are talking about) is different.
8.1 The sensor should be calibrated regularly. The cycle time is better to be no more than 6 months. 8.2 Do not use the sensor in the high dusty environment for long time. 8.3 Please use the sensor with correct power supply. 8.4 Forbidden to cut the sensor pin.Try to put it outside for 10mins and then short pins 8 and 12 (see the photo below). This worked for me when I had some weird readings
-
@korttoma
In the technical specification I only find the calibration with nitrogen. I don't think, that putting it outside, will help, as it is usually at around 400 ppm at the moment. (AFAIK netatmo sets the lowest measured value in the last one or two weeks to 400 for calibration).@FotoFieber Netatmo is using index also cannot be compared with mh-z14a.
I think the idea putting the sensor outside is to stabilise it - the reading is in the range of 300-400
-
@korttoma values are completely off. Co2 cannot go down below 300 level. This is a value of co2 outside (300-400).
You have to calibrate it regularly. Zero calibration (this is what you are talking about) is different.
8.1 The sensor should be calibrated regularly. The cycle time is better to be no more than 6 months. 8.2 Do not use the sensor in the high dusty environment for long time. 8.3 Please use the sensor with correct power supply. 8.4 Forbidden to cut the sensor pin.Try to put it outside for 10mins and then short pins 8 and 12 (see the photo below). This worked for me when I had some weird readings
@alexsh1 said:
Try to put it outside for 10mins and then short pins 8 and 12 (see the photo below). This worked for me
Where did you get this kind of information from? The MH-Z14.pdg I found online does not mention anything about this.
- Tomas
-
@alexsh1 said:
Try to put it outside for 10mins and then short pins 8 and 12 (see the photo below). This worked for me
Where did you get this kind of information from? The MH-Z14.pdg I found online does not mention anything about this.
-
I finally found some time to really look in to this 562 issue. I looked at the raw data in DataMine2 and I noticed that the 562 value appeared every 10 minutes on the minute.
Then I knew that this value cannot possibly come from the sensor. I search around in my Vera device for a bit and I found some lua code that copied the "Variable1" value from the sensor to the "CurrentLevel" every 10 minutes. Then I remembered that in the previous version of this sensor the value was reported via V_VAR1 and I had to copy it to another variable in Vera to be able to draw any graph. The current version of the sensor reports the value directly to the "CurrentLevel" variable and the value 562 that was still in the old variable was copied over the "real" value every 10 minutes.
I also previously had some really low values from time to time from the sensor mostly when responseHigh = 1 and responseLow = negative value
so I forced the responseLow to always be a positive value like this:
int responseLow = abs((int) response[3]);
I will keep an eye on the behavior of the sensor now that I have finally removed the confusing 562 value.
