City Air Quality

It is still work in progress, but last time I was busy building a new dashboard for the CITY units, one that uses the existing API to iterate the available sensor streams, than plot them in a visually appealing form.

This dashboard shows all gases, as measured by the CITY hardware. The charts are dynamic and synchronised: You can zoom one and the rest will follow, to make it easy to check the data.

I also need to add some horizontal bars to indicate the legal limits for air quality. This way we'll understand the numbers easier.

More on www.uradmonitor.com/products

Calibrated sensors

The electrochemical sensors used in this project, are individually calibrated in a test lab. They have a unique identifier, and so, for each - calibration data is generated after tests in the controlled environment.

Besides the 4 sensors that I selected for this project, there are other sensors for a wide range of gases. This is one of the reasons I designed the PCB with sockets, for interchangeable sensors. The other reason is that electrochemical sensors have a lifespan of about 2 years. That is because they work in a similar way to electrochemical batteries - they generate a current when the target gas is present. So with a limited lifespan, the maintenance of these units needs to be made as simple as possible - for a practical reasons considering city level deployments.

List of gases with compatible sensors

Getting back to the list of gases for which there are compatible Series-4 sensors:

Carbon Monoxide CO (0-1000ppm), Oxigen O2 (0-25%vol), Ammonia NH3 (0-100ppm), Hydrogen Sulphide H2S (0-100ppm), Nitrogen Dioxide NO2 (0-20ppm), Hydrogen Fluoride HF (0-10ppm), Sulphur Dioxide SO2 (0-20ppm), Chlorine CL2 (0-10ppm), Ozone O3 (0-20ppm), Ethylene C2H4 (0-100ppm), Formaldehyde CH2O (0-10ppm), Ethylene Oxide ETO (0-20ppm), Hydrogen H2 (0-1000ppm), Hydrogen Chloride HCL (0-20ppm).

Now that the chemistry lesson is over, I'll take you to another favourite hobby of mine, software.

Calibration parameters

The datasheet indicates two ways of accessing the data. There is the Digital format that comes with registry data that compensates the readings on the fly, and the raw analogue output where the compensation parameters need to be added to the data.

First option is the easy way, but for flexibility I went for the second. Raw data is being obtained from the 4 sensors and sent to the server. There, a database holds the unique sensor identifiers and the calibration parameters for each.

The calculations are easy:

Finally when you call the RESTFul API to see the actually readings from the unit, you get the final data, with the calibration parameters added to the result. Perfectly calibrated sensor readings.

The advantage to this is that maintenance work is reduced to a minimum: in case you need to replace old sensors, you just insert them in the sockets, then change the numbers on the server, in a simple dashboard.

The same approach should you want to configure a detector unit to work with different sensors, any from the list will work, you can even use 4 sensors for the same gas, for maximum redundancy.

The first assembled PCBs were a beauty:

The sensors fitted the sockets perfectly. After spending a few hours trying to access sensor data, it became clear that unfortunately, the device didn't work. On each of the 4 electrochemical sensors, the voltage output was a constant value, no matter the fluctuations in test gases (SO2).

What happened was that I did a mistake when drawing the sensor footprint for the PCB design: the positions were mirrored, so the pins were all wrong. A stupid mistake that rendered the PCBs useless.

To finalise this product I had to design an enclosure and I opted for anodised aluminium profiles. These can be cut to various lengths to match the PCB, you just need to make sure that the other sizes fit. Luckily the manufacturers offer a large set of profiles to choose from, and I was able to find one that matches the height of the sensors, but also gives some space at the bottom where the copper sockets are soldered, protruding the PCB limit.

Using the existing profile as a starting point, I had to identify PCB position and sensor sizes to do the holes, logos, and other silkprint elements. I opted for a black anodised aluminium finish with a white silkprint. As the design includes an air pump, holes for air intake and exhaust where added:

This construction started as a prototype, and I used it a lot in its initial form. I decided to make the next step, and use the field data and sensors tests to build a product out of them. For air pollution in cities, I checked the requirements on Air Quality Index and it became evident that many international evaluation standards go for 6 main parameters. These are Ozone, Carbon Monoxide, Sulphur Dioxide, Nitrogen Dioxide, Particulate Matter PM2.5 and Particulate Matter 10.

As I said my sensor homework was done, so I knew exactly what to go for. I designed a board with 6 electrochemical sensors and a laser light scattering PM sensor. The 6 electrochemical sensor slots would allow two additional gases to be detected, optionally.

Then, checking the BOM it was clear the costs are too high. 6 4Series electrochemical sensors in a box is not exactly cheap. And talking about the box, that became rather large too. So I removed 2 slots to meet just the Air Quality index requirements. Next was a few hours of fun, doing the PCB traces manually (like I always do):

As this will have built in Internet connectivity, the final device will be an IOT detector. I went for two connectivity options, one was LoraWAN and the second Wifi, to cover multiple usage scenarios in City deployments across various ranges and with different power requirement. Here is the LoraWAN:

And this is the Wifi variant:

I used some interesting new tools for part of the design, the online tools from EasyEDA. I also used their services to order the PCBs, as my DIY toner transfer attempts failed on this.

I had the chance to visit the former uranium mining colony of Ciudanovita in Romania, while having the detector installed on my vehicle. This is a story of what I saw, combined with the data recorded by the device.

Every gain comes at a price, and so the comfort of technology claims its cost at some other end. For nuclear energy – what it gives is known, modern living conditions, heating, illumination, transportation and all in one the civilised world as we know it. Yet what it takes sometimes remains in the shade, like what an environmental mess irresponsible uranium mining can be, and how hard it is to clean that up?

As for the device, this short trip proved its utility.

Additional resources:
Fosta mina de uraniu de la Ciudanovita neecologizata nici acum
Ciudanovita locul din Romania unde radiatiile de uraniu depases de 100 de ori limita de alerta
Moartea poarta numele de Ciudanovita
Marturisiri din Ciudanovita

To collect enough data I drove for a few hours across the city of Timisoara. Thanks to my beautiful assistant I got to have a demo video of the entire procedure:

There are three software components. One is the firmware running on the device, then a mobile application running on the smartphone (most likely an Android app) and finally the server side software that receives the data via HTTP Post, stores it in a mysql database and draws a heatmap for the frontend. The firmware is mostly focused on the sensors drivers and reading the data, the mobile app works as a relay getting the data over bluetooth and sending it to the server (the phone is a good solution for Internet connectivity) and the server component shows the results in a visual form.

Here are a few pictures showing a mobile app I wrote, that works as a Bluetooth relay, taking the data from the sensor unit and sending it only to the server:

It's obvious this was designed for Android OS, with a nice Bluetooth discovery option, a connect button, and lots of text boxes for showing sensors output. There are even 3 buttons to control the unit, the shutdown, and two for audio effects since the sensor board, based on uRADMonitor-D, also has a speaker: https://hackaday.io/project/4977-portable-environmental-monitor