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Smart Citizen Station - Extended with Anemometer, Rain, GPS, 4G Radio and Solar

This describes my project in outline:
Use Case: The goal is to comprehensively measure ground level ambient air pollution characteristics in a remote mobile scenario; in both urban and in pristine remote environments. We are concerned about air quality.

The Base system is a Smart Citizen Station comprising:

  1. Smart Citizen Kit V2.1 with Data Board (SAMD21G and ESP8266) and Urban Board: The base sensors are: Air Temp, Humidity, Absolute Air Pressure; Noise Level; Light Level; VOC Concentration. (Note: Dust Sensor is not fitted to urban board in this case). Wi-Fi Communications@ 2.4 GHz. is provided by ESP8266.
  2. Smart Citizen Station standard extensions to SCK include a PM Board with SAMD21G processor; and the sensors are External temperature (Dallas), and 2 x Dust Sensors. SCS also includes 3 x 16 bit Analog Digital Convertors to which are attached 5 x Electrochemical Gas Sensors. In this case we use sensors provided by Spec Sensors (USA) in place of Alphasense. This is due mainly to cost considerations. The sensors are CO, NO2, SO2, O3 and H2S.
  3. Others: We further extend SCS by adding:
  • CO2 Sensor SCD41; more compact than the standard SCD30.
  • NEO M8U GPS Board from Sparkfun.
  • Additional SAMDG21 Board to handle the Wind and Rain sensors because there were insufficient Serial ports available on PM Board.
    The Wind and Rain Sensors selected both have no moving parts; making them more robust in the remote mobile situation. They also have very low power consumption.
  • The Anemometer is made by Calypso Instruments (Spain) - their ULP model supporting polled serial connection at UART levels. It uses an ultrasonic technique to measure wind direction and speed.
  • The Rain Gauge is the well-known Radeon RG15 supporting Serial Communication at UART levels. It uses Infra Red beams to measure rain drops deflecting the IR beam (by changing refractive index) on a transparent dome. It’s a similar principle used to automatically control windshield wipers on a Motor Vehicle.
  1. Communications: We add a Wi-Fi to 4G LTE gateway made by D-Link.
  2. Power: The extra sensors and the 4G LTE radio add considerable power drain to the system making battery power difficult but because the system is remote, battery power is essential. We added a 370 wH battery and 2 x 60 watts flexible solar panels made in Taiwan by Googol Company. It is physically large and heavy.
    We also added a INA219 power measurement sensor to continually monitor power consumption.
  3. Mounting: The system is mounted on a robust surveyor’s tripod that is made by Stabila (Germany & China) model BST-K-L
  4. Display(s). We added 2 x 128x128 Pixel Monochrome GROVE OLED V3 Displays from Seeed Studios for local output of readings and debug. They are turned off normally, but light up for a few minutes when a button is pressed

It has so far taken several months to formulate the design of the system and gather all the parts. There were delays caused by COVID19. It will take some more time to complete firmware development and test the system.

Budget: This system no longer falls within the ‘inexpensive’ category of citizen science environment monitors such as SCK2.1; but it does prove that the basic Smart Citizen System can be extended beyond the limited capabilities usually found in commercial products; to form a more comprehensive type of monitor. Specifically the combination of toxic gas measurements, wind velocity and direction; Rain; GPS Position and Altitude are unique in the field of Environmental monitors. And because the Smart Citizen system is open-sourced, we know about every component, and we can closely examine (and change) the firmware; unlike a closed and copyrighted commercial system.

The comprehensive set of readings provide for interesting correlations to be observed, and for investigations to be carried out. For example we can now say things like “When the wind at this location X comes from the specific direction of Y, PM Dust levels increase along with SO2 levels, when there are dry conditions.”
Because the monitor system is mobile we can, using the one device, compare baseline readings from a pristine environment such as a National Park, with readings taken in an Urban environment such as a rooftop in an urban area; and the GPS data locks readings to a specific location.

One must carefully set expectations of the accuracy of readings from a Monitor such as this. Its not a highly accurate laboratory instrument. Price was part of the selection criteria for each type of sensor (although not exactly cheap in some cases).
Whilst each sensor is calibrated in the factory, and we take steps to calibrate readings ongoing for temperature and humidity effects and drift, one should NEVER make absolute statements about the accuracy of readings.
They are “best effort” within our budget. The readings will contain (relatively small ~~typically 10%) errors (indicated in manufacturers characterization data) that are consistent and there will be a stochastic element in each set of readings. One must use statistical techniques on each set of readings to confirm validity of any conclusions. But because the readings are taken at regular intervals with self-consistent error bars, the changes (delta) in environment characteristics over time remain reliable and valid.

The current status of this project:
Almost all hardware components have been assembled. Waiting only a couple of items.
Firmware development is started but not yet complete. When firmware development is complete details will be available via GitHUB as open source for the benefit of others wanting to do similar things.

Credits: I am indebted to the FabLabs Barcelona Team for their help in development of this system; in particular: Oscar Gonzalez (@oscgonfer ) has been my contact and mentor for the duration of this project and constructed the base SCS for this project.

Kudos: Both UPS and FedEx proved to provide excellent 5 star service all through this project, as did Digi-Key, Sparkfun and Mouser Electronics. We also like GW Instek a lot for making their wonderful MSO 2204EA Oscilloscope and great service.
Brickbats: I am unable to recommend: USPS, Deutsche Post DHL, Farnell group (Newark, Element14 etc.) (one star for each, with painful memories).

Interested in this project ? I am happy to field questions and encourage collaboration, comments and feedback concerning this project; within the constraints of time that I have available.


Very inspiring project! Thanks for sharing. Why do you need GPS? It seems as quite static device…

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Trust me it’s designed to be moved around, that’s why the tripod is included…
In general I expect it will spend a month in any one remote location to collect baseline data.
In fact the most useful reading from GPS is the altitude, because of the relationship it has with barometric pressure. It can be used to derive normalized sea level pressure.

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Small problems arise during fabrication and get solved. This problem was how to mount the Smart Citizen Station enclosure onto the tripod pole without having it turn around in the breeze.
I had to search all over the world for a suitable bracket.

It’s solved using a mount that is designed for a CCTV security camera. $US21 incl. shipping gets you two of these. It attaches to the enclosure using M5 bolts and nylon wing nuts.
It came with (very long) stainless steel bands.
I also tried nylon zip ties; but the stainless steel bands can be tightened more easily to immobilize the enclosure. The downside is that I will have to take electric drill screwdriver with me when installing it.

Here is a photo of the interior of my Smart Citizen station. It is almost complete needing only a few items. However it is ready to have firmware loaded and testing can begin.
The GPS Board is mounted top right on top of 2 PM Boards. The first PM Board services PM Sensors and an external ‘Dallas’ temperature probe. The 2nd PM Board services the Anemometer and Rain gauge.
Bottom left you can see an INA219 current sensor for monitoring power usage.
The ugly 6 way grove connector is needed because several sensors have only one Grove/Kwiic connector and cannot be daisy-chained.

Of interest is the wiring for the “Spec Sensors” gas sensors. These mount differently to the standard alpha sense gas sensors; requiring unsightly ribbon cables that are hand-soldered. The gas sensors are mounted beneath the 4 port ADC board each with windows to the outside air.

Here is a photo of the Anemometer and Rain Gauge mounted on top of the tripod pole.

The Anemometer comes from Calypso instruments (their Ultra low power model with Uart interface). it has no moving parts, and uses wind deflection of ultrasonic beams to service wind speed and direction.

The Rain Gauge is model RG15 from Radeon (USA) also has no moving parts. It reflects Infrared light inside the polycarbonate dome to photoreceptors. Rain striking the dome causes a change in refractive index, which is measured by the photoreceptors allowing the amount of rain to be calculated. It also uses Uart communications.

Both devices connect via waterproof cables and connectors to the 2nd PM board in the SCS enclosure.

Cool setup. Can we see it online?

It’s not yet ready. I am having a few problems “building the firmware” visit that topic on this forum to see the latest.

I have just moved house; I am hoping to restart work on this project in a few days after unpacking everything.

I now have 2 devices online. Although firmware for the SCS V3 is not yet complete.

The SCS V3 had trouble with the I2C bus; for which reason I am deploying a 8 Channel I2C MUX unit.
This requires further complex changes to the firmware; and so further delays.

However I do turn on the SCSV3 online from time to time. Thus far it does not have a complete set of readings.

Meanwhile so have also turned on my old SCK 2.1 kit at the same location.

So both can be found on the SmartCitizen map in Taichung, Taiwan ( you will not have any trouble finding it because they are the only active kits on the island.

Today I installed replacement USB cables used for power reticulation within the enclosure.
The old “straight” usb connectors were difficult to install, had side-strain on the connectors and interfered with boards.
The new connectors are of the “right angle” variety and make it easier to install the plugs with less strain and interference between cables and boards.
I also purchased a “bulgin” type cable used to plug into the enclosure with power. This new cable is to be used to connect the solar battery.

As always something happens; and so I have discovered the battery seems to have developed a fault.
Charged to full capacity it lasts only a few minutes before turning off. Given that it has 88 AH capacity that’s not what’s expected. I am of course chasing this down with the local company I purchased it from.
EDIT: The Manufacturer responded to my enquiry and provided advice leading to “fixing” of the battery problem I noted. All I had to do was charge the battery for > 8 hours continuously with no load. I did that and thus far the battery has powered both SCS V3 AND SCK2.1 devices simultaneously for > 24 hours xx 36+ hours

Just a note . Most of the discourse (blog) on this subject has been conducted under “building the firmware” section. I had forgotten this thread existed.

But of course it’s because that’s where all of my time has been spent.
It’s a mixture of firmware building; sensor integration and dealing with hardware unissues that cropped up during that process including largely the big project to integrate a I2C mux into the system. This was because the system just stopped working due to too many devices and no control over the manner in which they connect to the I2C bus.