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  • Mobile Fine Dust (PM10 & PM2.5) and NO2 Meter 5 months ago

    Without a GPS-signal the mobile meter will not log the data on the SDcard, but the data will be shown on the 7-segment display. So, to enable logging you have to comment out the code between line 453 and 463 where the retrieval of GPS data is done. The GPS-module itself however must still be present. If you want to get rid of GPS completely, a lot of other parts in the code have to be deleted or commented out. If you really want this last option, I can send you a redesigned code version.

  • Mobile Fine Dust (PM10 & PM2.5) and NO2 Meter 6 months ago

    A few months ago I answered a similar question from someone in India. My reply was as follows:

    If you order the SDS011 finedust sensor, you also get a flat cable with two connectors attached to it and a serial2USB convertor module. When you connect the sensor to this module with the flat cable, then you can plug the serial2USB module into a USB-port of your laptop or notebook. Of course, you always need some software to read the serial messages which the SDS011 sensor sends every second and decode these into readable format on the screen. I recommend to install Python and the CH341 serial2usb driver on your computer (you can get a free download of both on the internet). By running a small Python program (which I can always post to you) you can read the current PM10 and PM2.5 values on the screen and with a small extension, you can also log all measurements into a file for later consultation.
    This is to my opinion the cheapest and simplest solution to measure finedust concentration on a fixed location.

    So, you don't need an Arduino microcontroller to display PM-values on a laptop or notebook. If it's this what you are looking for, I can send you the Python program as well. If you need the mobile version as it is explained in this project, I can also send the set of the two PCBs to you with a description how to build one for yourself. Cost of these PCBs excl. shipping is about 50$.

  • Mobile Fine Dust (PM10 & PM2.5) and NO2 Meter 8 months ago

    Thanks for your comment: you've apparently found an error in the static declaration of the 'days' array. However the compiler does not treat this as an error, but indicates it as a warning. It is obvious that you cannot store the last 3 values (273, 304, 334) in a memory location of type uint8_t, it should be uint16_t. Reason why I didn't notice this was because warnings were suppressed in my IDE-settings. But by changing this type 12 extra memory bytes are needed, which causes the 'low memory' warning. Therefore I changed the 'days' array so that values indicate the number of days to be added from previous month at beginning of each month i.s.o. the cumulative number of days since beginning of the year. I also added more comments in the function 'hour_inc' and corrected another error in the last two if-statements. The new code has been inserted in the SW-description of the project.
    The use of the function 'hour_inc' is only relevant for those countries belonging to the GMT+1 timezone where the daylight saving procedure applies. For other time zones where this procedure applies other values in the 'hours' array have to be filled in. This function is not needed for time zones where there doesn't exist any daylight saving procedure and it should be replaced by a fixed integer reflecting the number of hours that the time zone is earlier or later than the GMT time zone.

  • Mobile Fine Dust (PM10 & PM2.5) and NO2 Meter 8 months ago

    Please send me your mail address, because I am not going to post this on this forum.

  • Mobile Fine Dust (PM10 & PM2.5) and NO2 Meter 8 months ago

    Hello Harald, I admit that the NO2-sensor (which was added to the mobile meter recently) is still not functioning properly. It is a SnO2 based metal oxide sensor which has to be heated to 220°C. Once that temperature is reached the resistance of the sensorstrip changes with NO2 concentration and this is shown in the datasheet of SGX Sensortech, but the single diagram they show holds only for 25°C and 40% humidity. Unfortunately I could not find further information for other ranges of temperature and humidity. Also, in the datasheet is spoken of cross-sensitivity with ozone, but no details are given how to cope for this.

    I've chosen for the 4541 because this was the only sensor available at AliExpress which was mounted on a small breakout board. However, it houses two sensors: one for NO2 and another for CO measurement. Since I am not interested in CO measurement I only use the NOX and not the RED output pin. The board also houses a MOSFET for preheating and a corresponding pin to enable this. I did not intend to use this, but since I experience a rather slow stabilization of nearly 20 minutes before the NO2 concentration gets realistic, I am going to test with a preheating time of 30 seconds and hope that this will considerably shorten the stabilization time. Also, I am going to remove the feeding resistor of 82 ohm for the heating of the CO-sensorstrip to save on battery capacity.

    Thanks for informing me about the existence of Breeze technologies, but on their site I could not find any relevant technical info, which seems normal to me because they commercialize their meters which are highly probable patented.

  • Mobile Fine Dust (PM10 & PM2.5) and NO2 Meter 8 months ago

    If you order the SDS011 finedust sensor, you also get a flat cable with two connectors attached to it and a serial2USB convertor module. When you connect the sensor to this module with the flat cable, then you can plug the serial2USB module into a USB-port of your laptop or notebook. Of course, you always need some software to read the serial messages which the SDS011 sensor sends every second and decode these into readable format on the screen. I recommend to install Python and the CH341 serial2usb driver on your computer (you can get a free download of both on the internet). By running a small Python program (which I can always post to you) you can read the current PM10 and PM2.5 values on the screen and with a small extension, you can also log all measurements into a file for later consultation.
    This is to my opinion the cheapest and simplest solution to measure finedust concentration on a fixed location.
    The measurement of NO2-concentration is a bit more difficult, since the sensor which I use and most sensors of this kind on the market provide an analogue output, so you need a microcontroller which can perform A/D-conversion and after that, some calculations have to be made to determine the exact NO2-concentration for which you also need temperature, humidity and barometric pressure as input.

  • Mobile Fine Dust (PM10 & PM2.5) and NO2 Meter 8 months ago

    Sorry, I have to correct you. It is nitrogen dioxide (NO2) which is a major cause of irritation of the respiratory system, together with ozone (O3). Carbon dioxide is not poisonous and does not cause any irritation, but it is a major greenhouse gas. The CJMCU-4541 gas sensor can measure NO2 and CO, but in this project only the NO2 or NOX output is connected, because measuring CO in open air is useless since concentration is negligible. There exists also gas sensors for measuring ozone, but I have not been able yet tot test these. This mobile meter already measures five parameters: PM10, PM2.5, temperature, humidity and NO2. I need more I/O-ports and a bigger housing if I would connect more sensors!

  • Mobile Fine Dust (PM10 & PM2.5) and NO2 Meter 9 months ago

    Thank you for the very useful tip! I will adapt the schematics of the display board using the 74HC4511 which reduces the number of SSI's from 13 to 7 with no impact on the sketch.

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