uRADMonitor A3

A versatile IOT device designed to track 8 air parameters and map pollution, with both wired and wireless Internet connectivity

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I planned to extend the uRADMonitor network and go from Radiation monitoring to Air pollution. Back in 2015 I was creating the "Portable Environmental Monitor" a HAD Prize Finalist. As a continuation of this effort, here's a new addition to the family of uRADMonitor detectors. Named A3, this is my forth hardware product, a new IOT devices that adds powerful sensors and new connectivity options to map the air quality. It was part of the Alba Iulia smartcity implementation, in Romania, in a joint effort with Orange.

Ridiculously advanced air quality monitoring station, enclosed in a compact aluminium body for rugged design, it has sensors for Gamma radiation, formaldehyde, CO2, tVOC Air quality +temperature, barometric pressure, air humidity, and a laser scattering sensor for PM2.5 particulate matter. The A3 also comes in 4 variants, with the same sensors but offering different connectivity options: Ethernet, Wifi, GSM (with a data sim card) and LoraWAN.

Detection interval

– background Gamma Radiation: 0 .. 9999μSv/h
– PM1.0/2.5/10.0 particulate matter: 0 .. 1000μg/m³
– formaldehyde: 0..5ppm
– CO2 400..5000ppm
– air temperature: -40 .. +85C
– air humidity: 0 .. 100% RH
– air quality / VOC: 0..100mg/m³ reducing gases and 0..10mg/m³ oxidising gases
– barometric pressure: 300 .. 1100hPa

– HW105+ only: noise pollution: 30dBA .. 130dBA

May 2017 - HW105

Finally, both attempts that failed in HW104 were brought to a solution. A sound amplifier circuit based on MAX4466 allowed good dBA noise calculations, while a new VOC sensor was tested, with excellent results. Finally, the uRADMonitor A3 has noise pollution detection capabilities:

Picture shows elevated readings due to auto traffic during day, with data from two nearby units functioning concomitantly.

February 2017 - HW104

I wanted to add a sound sensor, and find an alternative to the VOC detection currently implemented with the BME680 from Bosch. I tried an electret microphone amplifier circuit and the GM502B sensor, but wasn't happy with the results. Design dropped.

September 2016 - HW103

This variant was a success. 4 PCB versions to hold the same sensors but offer 4 different connectivity options: Ethernet (via enc28j60), Wifi (via ESP8266-ESP04), GSM (via SIM800) and LoraWAN (via RN2483 / RN2903).

The enclosure was reworked as well, to use a new profile that comes with wall mounting brackets. The one that came closer to my size requirements had a smaller width and this impacted the new PCBs. I also made two types of enclosures, one with a rectangular opening for the Ethernet cable connector, and one with a round hole to fit the SMA antenna connector, serving all 3 radio variants.

The sensors in these units stayed the same. Bosch BME680 for temperature, pressure, humidity and VOC, the laser light scattering sensor for PM2.5, the NDIR CO2 sensor and the electrochemical formaldehyde sensor. The SI29BG Geiger tube remained responsible for the radiation readings. This tiny unit of about 11cm long, was therefore capable to measuring 8 air parameters, sending the data over 4 distinct channels: Ethernet, Wifi, GSM or LORAWAN.

The system drew the attention of Orange, and I started a partnership with them to install several such units in a few cities. One such example was the city of Alba Iulia, the first Romanian smart city, where 15 A3 units were installed in public transportation. The data is available online, here.

This became an excellent way to use my toys in the real life environment, but also to learn to raise up to the challenge of making everything work as expected. Some time after, the system is still functioning unattended, providing precious readings on the air quality. For a few months I was busy building by hand a few tens of these devices, running tests and making sure everything is perfect. But it was worth it, and I'm proud of the accomplishment.

And talking about the data, here are some of the tests, showing the output from several devices running in parallel. These are PM2.5 measurements, counting particles as small as 2.5 microns in diameter, and you can see the devices agree on the values:


July 2016 - HW101, 102

These versions had some issues. First I tried to use the previous HW100 design, and add extra connectivity options: instead of the Ethernet module for wired connectivity, I needed more options: Wifi, GSM and LoraWAN. Replacing the Ethernet module with modems for the radio variants was easy, but I placed the 8MHz crystal oscillator too close to the High voltage inverter...

Read more »

  • 1 × enc28j60 Development Kits, Boards and Systems / Adapters, Adapter Boards and Sockets
  • 1 × ndir co2 sensor
  • 1 × electrochemical CH2O sensor
  • 1 × BME680
  • 1 × Laser PM2.5 sensor

View all 10 components

  • Crowdfunding - 25% in less than a day!

    Radu Motisan11/23/2017 at 23:22 0 comments

    "With 800 units deployed worldwide, the A3 is probably the best uRADMonitor product, with a plenitude of advanced sensors and built-in Internet connectivity to monitor your location 24/7.

    We're grateful for all the support we received so far, this includes our first successfully funded indieGogo campaign.

    Pollution is a global phenomenon impacting each and all of us as air knows no boundaries. We need to put more of these units in places where people can't afford them but are most affected."

    This was the call to action, and the community responded. Less then 24hours later, the project was already funded 25%. Check it out:

    Now it sits on position 2, on trending Top for the "health" category:

    w00t! awesome

  • #smartcity

    Radu Motisan07/16/2017 at 20:38 0 comments

    Big news, the A3 is now part of the first Romanian Smart City implementation, with complex air quality monitoring systems in Cluj-Napoca, Alba Iulia, Bucharest and Timisoara.

    Several uRADMonitor A3 detectors have been installed in public transportation buses and in parks. The collected data is centralized in real time, offering valuable knowledge on pollution and its evolution in time, from a location to another. With this approach, the entire cities are mapped with just a few units:

    Live data examples here:

  • HW105, succes!

    Radu Motisan05/14/2017 at 17:51 0 comments

    I tried to detect noise pollution levels in HW 104 but failed due to improper circuit design. Back to the drawing board, I opted for the MAX4466 where some know how was already available, thanks for the efforts of @ladyada / @limor . With this approach, results were immediate:

    The chart shows noise levels as recorded by two A3 units operating alongside, for a few days. The elevated values are due to traffic noise, more prominent during the day. I used a sound-meter for some calibrations. The data is exported in raw format, and calibrations are done on the sever, so I can have more control over the output. But all in one, having identical readings from two separate hardware units was a nice achievement.

    As for the new VOC sensor, I tested the MP503, a similar tech to the previous GM502B, but due to bigger size it was more resilient to soldering and I was able to install it, without affecting its initial performance. Again, two units were tested, and the readings went in tandem.

    Similar to the BME680, these sensors have a simple principle. A heater is placed near a metal oxide semiconductor. If the air is contaminated with various substances (as those belonging to the VOC family), various REDOX chemical reactions will take place, affecting the semiconductor conductivity.

    What happens is that if the air is more contaminated, the sensor will become more conductive. So on a clean air we will read a higher resistance, while a polluted air will bring the sensor resistance down. This is how the ohm are linked to air quality on these kind of sensors. The only issue is the readings will fluctuate with environmental temperature and humidity, so for absolutely perfect readings, the data will have to be calibrated against the two, according to the chart in the datasheet. A linear function will do it nicely.

  • HW104 Iteration

    Radu Motisan05/14/2017 at 17:37 0 comments

    The A3 was a popular design, that worked well both during winter and summer, both as a fixed monitoring station and also when installed in buses, withstanding constant vibrations and traffic conditions. Due to interest in its huge potential, I continuously invested time and effort to make it even better. First I researched alternatives to VOC detection, implemented with the BME680 sensor from Bosch. VOC detection is far from perfect, first because the way this works, a heated filament doing REDOX reactions is not quite exact science when it comes to measurements.

    HW104 adds a new VOC mems sensor, the GM502B. This is an analogue sensor, meaning it only has a filament and a semiconductor crystal, and I had to do the heating and VOC calculations based on the crystal resistance changing proportionally with air quality. Initial tests where great, but soldering caused many problems. I tried about 10 sensors and they where all damaged during soldering, no matter what temperature settings I used. Discussing the problem with the factory didn't lead to any results.

    My ambition was to add noise pollution detection to the already crowded PCB. A circuit based on an electret microphone with a simple amplifier feeding one ADC port was designed:

    I wasn't happy with the noise detection results either. The good thing was both changes (sound + new voc sensor) were optional, the HW104 board could still be used with the previous sensors (BME680), so these weren't such a big loss.

  • Fixing the issues, HW103

    Radu Motisan05/14/2017 at 17:14 0 comments

    Here's the new PCB layout, HW103, with multiple changes: new PM2.5 sensor footprint to match the current factory version, removed zener/mosfet based DC In protection circuit in favour of a better DC-DC 6-28V converter circuit, allowing operation on variable input voltages and finally a new aluminium enclosure with wall mounting brackets to make installation easier.

    The previous rounded aluminium boxes where neat, but installing those in buses was problematic. I had to opt for a different aluminium profile, and do the manufacturing all over again, including new holes and silkprint. With this variant I also needed different holes first for the Ethernet variant, and a new panel for the radio boards that replaced the cable for the SMA connector holding the antenna.

    The above picture shows a LoraWAN A3 unit operating from below ground level, in a cellar. The same unit was tested to successfully connect to the gateway from about 2km distance with just that tiny antenna. Surely, it can do much more, as the datasheet mentions the 15km figure.

    These units performed great! For me it was a busy summer assembling a few tens of these, for a new partnership started with Orange, as a result of winning the Innovation Labs 2016 competition.

    Some of these units went in Alba Iulia, the first Romanian Smart City, others in Bucharest. The major benefit that came out of this was that I had the chance to work with city data, see the major pollutants, but also understand how the hardware behaves in the field. I can say that the units were very resilient, considering some of them got installed in buses, withstanding vibrations and harsh conditions during winter/summer.

    A passive POE adapter proved useful to simplify the installation in buses, for the city of Alba Iulia.

    The DC-DC built in converter was extremely useful, given the various voltage lines available in buses. These converters would output a nice and clean 5V voltage for the uRADMonitor A3 internals. The solution passed its QA tests, and I am very happy with it.

    These buses also have a GPS receiver, part of a different system, and the position data is aggregated to the uRADMonitor A3 air quality data. This way I was able to build a real time map, and see the readings based on location (both spatial and temporal coordinates):

    This is available online on the uRADMonitor portal, or on the Alba Iulia #Smartcity dashboard.

  • HW Iteration 102

    Radu Motisan05/14/2017 at 16:46 0 comments

    After the successful deployment in public transportation of 10 uRADMonitor A3 units, in the city of Cluj Napoca, it was clear that such field deployments need more flexibility in terms of connectivity if it was to cover more ground faster. So I designed a new PCB, version 102, to add just that.

    The Ethernet module would be replaced by a Wifi ESP8266-ESP04 module in the uRADMonitor A3 Wifi variant, a SIM800L module for the GSM variant, and finally a RN2483 from Microchip in the LoraWAN variant. The last one is an exciting new direction, as it provides radio link of up to 15km with minimum power requirements. The sensors stay the same:

    The joy was short, as soon after receiving the PCBs and doing the first tests, it was clear there were major issues:

    1. the PM2.5 sensor received an upgrade in the factory, and the new units had a different footprint, incompatible with my PCB design

    2. there is some kind of weird RF interference generated by the High voltage inverter inductor, affecting the 8MHz microcontroller crystal. This renders the unit unstable.

    Oh well ... back to the drawing board.

  • First 10 units go for #SmartCity

    Radu Motisan07/08/2016 at 18:50 2 comments

    The first 10 units were assembled, tested and shipped for a first #smartcity #uradmonitor implementation. I'm happy about the way I came out with the aluminium enclosure, the end plates were designed to fit inside the main body, improving the overall look and feel.

    This enclosure is not waterproofed, as it needs to have an open intake for air, and also an exhaust opening. Here are the 10 units ready to be shipped:

    These first units are to be installed in public transportation in Cluj Napoca, to keep the users informed on the quality of the environment, but also, due to the chosen bus line that practically crosses the entire city, we'll get valuable data on pollution. For the end users, a simple dashboard presents the more relevant details, together with an air quality score and recommendations:

    The big data analysis tool to serve the SmartCity component is currently under development. It will offer interesting insight on the correlation of pollutants (eg. PM2.5) to traffic hours, periodicity and other useful patterns.

  • The tests and the dashboard

    Radu Motisan06/03/2016 at 19:56 0 comments

    Developing this project took about 2 months, from sourcing the sensors, running initial tests, then conceiving the PCB, assembling a few test boards, writing the firmware and then the server side dashboard and communication protocol. All seems to go well so far, we need to implement a dashboard to show the data to the users, but also run more stability tests and implement fixes where needed.

    It was a fast paced ride, like most of all I've been involved in lately, but a rewarding one since things turned out nicely, and this product seems to be a successful one right from the start. It maps useful parameters, and it will help collecting valuable data regarding our environment.

    Don't forget to visit to see the bigger picture of what this is all about.

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Enjoy this project?



Tobias Müller wrote 03/10/2018 at 17:19 point

Hi Radu,

I saw you moved to SMD components for your HV generation. Would you mind sharing which components you used?

Best regards


  Are you sure? yes | no

Radu Motisan wrote 03/10/2018 at 17:37 point

Mainly they are 0805 sized components, for the HV feedback I used a stream of 4 4.7M 0805 resistors, while for the tube resistor, a series of 4 2.7M resistors. There's also the voltage multiplier that uses HER108 SMD HV fast diodes, and X7R 10n / 1KV capacitors. The rest is easy, but let me know if you need anything else.

  Are you sure? yes | no

Tobias Müller wrote 03/10/2018 at 17:54 point

Thanks for the very quick reply! I'll order some of them and try to get my SI-8B to work!

  Are you sure? yes | no

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