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The all-new Urban Sensor Board in the Smart Citizen Kit 2.0

Hi everyone! :raised_hands:

Last Christmas, we received a very nice gift in Smart Citizen with some new prototypes of the upcoming V2.0. Nice, huh!? The team is right now working hard on it and while we ultimate some details, we would like to give you some insights about how it will look like!

There is a wide refurbishment of the board in general, aimed to improve previous versions and offer broader and more robust functionality, in this post we’ll cover the most interesting part of it. Let’s talk about the changes in the Urban Sensor Board!

Air quality

Interested in participating in the low-cost air-quality sensing revolution?
We’ve got you covered!

The SCK 2.0 will feature on the air quality side the well known Metal Oxide NO2 and CO sensors from SGX SensorTech 4514 from previous versions. Under the hood we find two resistive sensors aimed to perform oxidation (OX) and reduction (RED) interactions with CO and NO2 present in ambient air, that have been object of study by scientific institutions in Europe in order to assess their potential, with very interesting results:

Image Credit: SGX

Along with the two SGX sensors, we have included a Dust particles sensor MAXIM MAX30105. This device is a high sensitivity optical reflective solution for detection of a wide variety of particle sizes. It integrates red, green, and IR LED drivers to modulate LED pulses for particle-sensing measurements and it is aimed for measuring relative air dust levels. Nevertheless, we are aiming to push further the possibilities of the MAX30105 and we are developing algorithms to support PM 2.5 or PM 10 relative measurements. Also, since it comes with an IR Led sensor, it can even be used as a proximity sensor!

Image Credit: SparkFun

Ambient conditions

Alongside with air quality measurement, one should consider environmental conditions in order to gather functional data for pollution control. For this reason, the SCK 2.0 includes an Relative humidity and air temperature sensor SENSIRION SHT31. This sensor provides a wide measurement range, high resolution and long-term stability, and it represents an upgrade from previous versions in terms of reliability and accuracy.

Image Credit: Sensirion

Furthermore, we should not forget the role of ambient barometric pressure for environmental analysis. This will be introduced in the upcoming kit with the NXP MPL3115A2, featuring a resolution able to help gather data from climate conditions as well as Above Mean Sea level (AMSL) height:

Image Credit: NXP // Funny how it looks similar to the MEMs microphone, right?

Finally, to conclude with the ambient conditions monitoring, carrying over with the traditions from previous versions, we feature the ambient light sensor ROHM BH1721FVC:

Image Credit: ROHM

Noise level sensor

Missing something? Last but not least, one of sensors that will be introduced in the 2.0 will be the smartcitizen-forum-famous I2S Mems Microphone from TDK-Invensense ICS43432. For this one, we cannot do better here than the wide range of posts in the forum about this sensor and it’s very interesting potential for urban noise pollution analysis. Check them out!

Image credit: TDK-Invensense

We’d love to listen to your thoughts about these sensors and your ideas for them! :bulb:
Drop some comments below!

Happy sensing! :blush:


Here the Urban Sensor board prototype:

We are finishing the last details before we launch production! :nerd_face:



If you are interested in getting one of the new Smart Citizen Kits 2.0 helps us by filling this form.

We are collecting information to size the first production batch and learn more about how do you plan to use it!


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What will the cost be (approximate!) for the V2.0 board?


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I’m getting a lot of interest from other teachers at my school as well… Will there be any bulk pricing for boards?

I see that you’re using an ESP8266 so some questions about this:

  1. Is this the main processor as well as WiFi provider?
  2. Are you making use of the ESP8266’s features such as the ability to sleep the processor and WiFi to save power?
  3. Will you be supporting OTA (other the air) software updates?
  4. What about full MQTT support, perhaps as a different software image?
  5. Any ideas as to power requirements, especially around LIPO/solar power? Same as the 1.1 kits or more/less?

Hi @paul1

Thanks for the questions. Here the answers:

Is this the main processor as well as WiFi provider?

No, it’s only the Wi-Fi provider. The main processor is an ARM Cortex M0, the Atmel SAMD21, the same as the Arduino Zero. We choose that for power efficiency, the ESP stays off most of the time and because we are working on other communication platforms like LoRaWAN

Are you making use of the ESP8266’s features such as the ability to sleep the processor and WiFi to save power?

Yes, we can make the ESP sleep and even cut it’s power complely from the main processor.

Will you be supporting OTA (other the air) software updates?

We did some tests on that but it won’t be ready for the launch.

What about full MQTT support, perhaps as a different software image?

The Kit uses MQTT for all the operations.

Any ideas as to power requirements, especially around LIPO/solar power? Same as the 1.1 kits or more/less?

It uses a LiPo as before, we support PV panels and we are also testing induction charging, like phones, to charge over your window glass. We’ll publish about this soon.

You can also follow the firmware development here:

Why is the ARM more efficient that just using the ESP? The ESP can be programmed to ‘sleep for…’ and will wake itself up at the appropriate time. What is the ARM doing when not sending data via the ESP? Does it need to keep processing all the time?

The SAM keeps everything working from managing battery or user interruptions, maintaining the RTC or performing the FFT analysis of the microphone signal while also going to uA sleep and all this for less than 2€.

Moreover, that means we can quickly change the radio module, for instance, we are working on a LoRaWAN version, and we don’t want to change our whole firmware architecture for that.

You should keep in mind we only turn the “radio” when we needed, and this can be once every an hour to publish the readings online, or even we keep it entirely off when we record data internally in remote locations.

We have been using several SCK1.1 for almost three years (you can see our real time data dashboard here: .

We have observed that CO and NO2 sensors behave quite wierd. After a thorough observation of the collected measurents, we have found that they are quite sensitive to O3 (ozone). In fact, in an experiment within a calibration chamber, we noticed that the NO2 sensor is an excellent O3 sensor!!

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Interesting analysis there! Thanks for sharing it here! :tada:

You are right! It is well known that NO2 and O3 sensors generally suffer from cross-interference, and this is a common issue in low cost sensors. Also, MOS sensors pose challenges for air monitoring in other regards: they are affected by temperature, humidity and this means that we need to use more advanced post-processing techniques for them to provide with proper results.

If you are interested in these topics, we have been working on a broad documentation about the sensors here:

More complex sensors are also in here:

Also, we have developed a framework for sensor data analysis based on python, fully open and documented here:

Using all this, we are working on the development of models for both, MOS and Electrochemical sensors and will be publishing some results in the following months.

Also, we will be happy if you want to share your insights with us, feel free to drop me a message if you want! It would be interesting to see how you did the testing :slight_smile:


Thank you for the feedback!

I have more data. The following charts compare the data collected yesterday by one of the costly municipal environment stations at Madrid with the data collected by Smart Citizen Kit collocated (20 meteres apart). You can see clearly the effect of the O3 interference in the SCK NO2 sensor (MICS 4514). On the other hand if you compare the official NO2 readings with the SCK CO sensor (yes, the CO sensor!!), you can see they are quite similar!

We have data collected during three years, so we could make a more thorough analysis. If interested, let me know.

You can find further information of our platform for collecting data here:

Hi again,

Thanks for the reply! Data looks quite interesting.

Bear in mind that the the measurements from those versions of the SCK are not corrected. Also, CO measurements should be inverse to the measured resistance, since the resistance of the MOS is inversely proportional to the CO in the air (more qualitative info in the datasheet).

Finally, let us know if you perform a more advance analysis, and if you want, use the framework above! It would be nice if you could show a deeper analysis of that long data collection!

Yes, we are making use of the charts in the datasheet in order to convert resistance values to mg/m3 and ug/m3 ( see our article in sensors magazine).

We will have a look to your framework!