CO₂ and Particle Meter Analysis DM306 / WS1125

Last modified April 29, 2021

What is special about the DM306 CO₂ and particle meter, will you ask me to do an analysis of it, you will ask me?

As it turns out, on one of my long walks on AliExpress, I came across a very cheap CO2 and particulate matter meter, which I had already seen many times, but there was something that this time caught my attention: they were selling it on the official Winsen website.

Winsen He is an old acquaintance, mine and of the regular users of this blog. It is the manufacturer of the MH-Z19 CO₂ sensor with which I built the first home wifi CO2 meter more than five years ago, what the original home CO2 meter posted on this blog was based on (although after a short time I started recommending another similar sensor).

This manufacturer has a Good reputation, since it manufactures sensors of a more than acceptable quality at an economical price.

What caught my attention on this meter was its price. Some € 40 for the version that only has a CO2 meter and € 50 for the version with a CO2 and particle meter in suspension PM1.0 PM 2.5 and PM10.

Of course, considering that only one CO2 sensor from this manufacturer costs about € 18 and a particle sensor about € 17For 15 euros more they offered us a finished commercial device, with a display of a very acceptable size and easy to read, rechargeable battery, audible alarm and all in a box with a very nice design.

I immediately thought: "I have to buy one, find out what's inside and see if it works for us.".

Said and done, in less than 10 days I already had it at home.

In this article I am going to tell you the following:

  1. Unboxing Meter: What the buyer actually receives, what the box includes, and first impressions.
  2. Analysis Meter: How does it work in general? How about its battery, charging time and autonomy? How about its accuracy and precision, can we trust your measurements?
  3. «Gut 'or teardown: What components is it built with?
  4. Reverse engineering: Analysis and reverse engineering of its operation, protocols of its sensors, etc.

There is a fifth part that is my favorite, but you will have to wait for me to finish it to see it. ANDl hack: The fun part! Can we do a «eMariewinsenstein" with the? Can we improve it and provide it with additional functionalities? I'm finishing it. You can not lose this!

Unboxing the Wins DM306C or WS1125

The first thing I will tell you is that it is not at all clear what its name or its manufacturer is, really. On the outside of the box it says absolutely nothing about it, neither manufacturer, nor model or anything. Clearly a product to be sold massively through multiple brands.

The only indications on the box are: "Air Quality Monitor" on the top, "MADE IN CHINA" on the side and a few logos of certifications and environmental information. Nothing more.

Not even in the manual it says absolutely nothing about its manufacturer or model. Only "Air Quality Monitor Instruction Manual".

Apparently Winsen gives him the name of model WS1125 but many other sellers give him on behalf DM306 or DM306C and even on its printed circuit board is engraved «DM306G_RB«.

In Spain it is sold in Amazon with brand Tackly, specifically as TACKLY-03, and its description is «Tackly Ambient CO2 meter».

TACKLY room co2 meter - co2 detector with indoor air quality meter - digital hygrometer humidity meter and digital thermometer for home
  • REAL-TIME DATA MONITORING - This is a gas monitor that is capable of accurately and real-time monitoring of CO2 concentration, air quality, ambient humidity and temperature. The product is embedded with a high-performance chip of a sophisticated infrared sensor, uses Big data algorithm recognition, has advanced technology, can already evaluate and monitor effective and real-time data.
  • 4 IN 1: AIR QUALITY CONTROL PM2.5 - Multifunctional air quality detector, as it effectively measures CO2, air quality (PM2.5), temperature and humidity. It has independent NDIR sensors for the measurement of CO2, temperature, humidity, and a laser scattering sensor for air quality (PM2.5).
  • JOINT AND WIDE DISPLAY - It has a large wide digital screen with unified record measurement on a common screen. Compared with ordinary and old air quality detectors, its interface design is more concise, intuitive, with clear area division and excellent texture.
  • PORTABLE and VERSATILE - This TACKLY measuring device has a lightweight design that makes it easily portable thanks to its small size. It is easy to transport and you can put it wherever you want, therefore, it can detect the quality of gas in terraces, bars, bedrooms, living rooms, kitchens, offices, cars, schools, hotels, camps. 24-hour real-time monitoring to protect healthy life and safety, ideal for the Christmas holidays.
  • CE / QUALITY APPROVAL - The TACKLY CO2 and air quality meter is approved by EU bodies, and presents CE certification, guarantee of use and product quality. In addition, the CO2 alarm detector is made of high-quality waterproof ABS material, and the data is updated in real time at 1.5 seconds at a time, ensuring a very high consumer experience.

The truth is that, by now, not surprising at all, since this is a way of acting very common in Chinese electronic products of low price (and quality).

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The box comes with a scratch on one corner, as if it had been dragged across the asphalt from China to Madrid. But how it comes quite well packed (a strong plastic envelope, lined with duct tape and several layers of bubble wrap) and the cardboard of the box is very hard, there are no major problems and content is intact.

Inside the box we find the meter, embedded in a custom plastic so that it does not move in the box, a micro USB cable and a concise manual in English. (Luckily, it's not in Chinese!).

The meter box is a pretty average white plastic, with a nice design that reminds of an alarm clock radio and keeps it from looking like a square hulk and helps it look good anywhere.

Already off, the screen looks quite generous, we will see how it looks when turned on. It comes with one of those self adhesive protection sheets to prevent scratching.

By the way, speaking of clock radios, the screen is a rather curious LCD type with soft side lighting that makes it not disturbing if we have it on the bedside table while we sleep.

Analysis of the DM306 CO2 and Particulate Meter

The moment of truth has arrived, the moment to turn it on.

I connect it with a mobile charger (not included) to its micro USB connector, I press the only button on the device and the meter turns on with a side-lit display with large characters that looks very sharp.

In the first seconds it provides us with some meaningless measured accounts and, after a few seconds, start giving us more realistic measurements.

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It doesn't take long to stabilize and give some values «logical«. Maybe a minute.

As the measurement increases, towards that stabilization, the meter begins to emit a insistent 'beep' every few seconds. I check that concise manual and see that the meter has an audible warning when 1000 ppm is reached.

In the manual it says that by double-clicking on the button on the front you can enable and disable the audible warning. What there is no indication on the screen of whether the audible warnings are active or not, so I have to do a few double-click attempts with different pulsation speeds and cadence between them until, finally, the prompts stop. Finally, it consisted of making two quick presses on that single button.

By the way, the threshold for it to activate the audible alarm is fixed at 1000 ppm without the possibility of modifying that value. A shame

CO2 measurements are somewhat lower than my other meters. At low concentrations, the differences are around 50-100 ppm and at higher concentrations (around 1500-2000 ppm) the differences rise to 100-200 ppm.

Even if there is a certain deviation, the measurements seem correct enough for a device of this cheap price. Let's think about what this device really does: it is capable of detecting 400 CO₂ molecules out of a million air molecules. It seems to me that it has a lot of merit.

Would it be a recommendable device to know exactly the concentration of CO₂? It is probably not an adequate meter to know the amount of CO2 that is in the environment very accuratelyBut keep in mind that what we normally want is to have 'an idea' of the relative changes in CO2, especially at lower concentrations, and for this it is adequate and does the right job.

In other words, at concentrations below 1000 ppm (which are the ones we are most interested in) the reliability of the measurement is sufficient to know that we are "between 400 and 500 ppm" or "between 600 and 700 ppm." This is sufficient in the vast majority of cases.

Along with the CO2 concentration measurement, which appears in larger characters and with more prominence on the screen, the data from the suspended particle meter appears.

The meter provides us with data on the amount of particles that are in suspension in the air at all times, updating that value every few seconds and separating them by particles of different size.

This meter provides us with data on PM1, PM2.5 and PM10 particles, which are the standard values (particle sizes) that are usually used for the measurement of this type of "dust" in suspension.

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In order not to take up much space on the screen, and to give more prominence to CO₂, the different measurements of PM1, PM2.5 and PM10 particles they appear in succession, every few seconds, one after the other.

Speaking of the accuracy of the measurements, precisely one thing that caught my attention (used, as I am, to analyzing the technical data of many CO₂ sensors for our projects) is that no precision data appears anywhere.

The precision data of the CO2 meter has been swallowed up by the earth. Not in the advertising, not in the manual, not in the box, not on the Winsen website ... nowhere does it tell us anything about it.

This lack of technical information from the manufacturer already tells us that we are not facing a high precision device.

In the tests that I have done, the precision in the concentration of CO₂ has been inferior to that of the other sensors that I use (Senseair S8 LP, which I use as a reference sensor, Senseair Sunrise S11, Winsen MH-Z19A, Winsen MH-Z19B, Winsen MH-Z19C, Netamo, Cubic CM1106SL-NS and other older Cubic models.)

PM1, PM2.5 and PM10?

This PM1, PM2.5 and PM10 is how meters refer to different sizes of suspended particles. PM1 are the 1 μg particles (microgram or millionth of a gram, a very small measure, really), PM2.5 those of 2.5 μg and PM10, if correct, those of 10 μg.

The meter tells us how many micrograms of particles of each of these three sizes are in the air for each cubic meter.

In this case I cannot tell you anything about the precision of the measurements, since I do not have any instrument of this type with which to compare, although Later I will tell you about the sensor that it incorporates and I will be able to make some estimates.

The CO2 monitor also includes temperature and humidity sensors. It seems very successful, given the market this device is aimed at, complementing the air quality data very well.

The tests I have performed for the accuracy of temperature and relative humidity have been quite acceptable, especially considering that most devices of this type are not usually very accurate.

In my office I have, due to all the projects and tinkering that I do, many sensors of temperature and relative humidity, starting with the sensors, quite accurate, of a Davis Vantage Pro 2 weather station, and continuing with sensors from Oregon Scientific, Digoo, Texas Instruments 18DS20, Bosch BME280, DHT22 and others. This allows me to make averages between them, which are supposed to give me figures that are quite close to reality. The temperature has been kept within 1ºC of difference and the relative humidity in approximately 5%, which is not bad at all.

In terms of controls, the meter has a single button, on the front panel, which allows us to turn it on, with a short press, turn it off, with a long press, switch between degrees Celsius and Fahrenheit, with a press when it is on, turn off the timer, keeping the button pressed for a few seconds and activate and deactivate the alarm with two short and quick presses.

There are no more options. No calibration options, historical charts, or menu of any kind.

The meter incorporates a rechargeable 2000 mAh lithium-ion battery that gives it about 8 hours of autonomy (in my load tests I have been able to verify that the reality is very similar to this value, with more than 1900 mAh of charge).

I have measured the full charge time in just over three hours and a half, although observing the evolution of the load current, I have been able to verify that it reaches a respectable load (let's say the 80%) in much less time.

The autonomy is not bad at all for a meter that, let's not forget, not only measures CO₂ but also suspended particles (which is done using a technology that tends to have a high relative consumption).

My conclusion from the analysis

It is not a precision device, but its low price makes it quite interesting for people who want a device to get an idea of how much CO2 is in the air and to be able to ventilate. I don't think that's their market either.

Logically there are more precise devices, but also their price is much higher (especially if, like this one, they also have a particle sensor).

That it includes a battery is also very interesting, and I would even say surprising, given the price of the meter. Its autonomy is more than enough for a day of measurements using the meter as a portable.

A positive point is that the battery is completely standard, of the 18650 type, so we can replace it with relative ease if it breaks, although it is welded and the plastic cover is stuck and it is not easy to open.

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