The Interactive Air Quality Map - A Step Towards Portable Monitoring in Lagos

The date is September 8, 2023, It's a nice Friday when you have just received a package from JLCPCB in the mail; you can imagine the kind of weekend I am about to have. I spent the weekend populating the components on the PCB, and before I delve into the challenges I faced getting the PCB to work as intended, I will summarize the schematic and PCB design for the new logger.

My microcontroller of choice is the ESP32 chip. I chose this chip for its well-known IoT capabilities. The other main components on the schematic are the SEN55 air quality sensor from Vlog 12, the MAX-10S GPS chip, and the A9G SOC, which is the same as the module used in the original mobile logger made from the ESDK in earlier days of the project. There is also an onboard SD card for on-device air quality logging, and since this is meant to be a mobile device, there is a battery charging circuit integrated.

Creating the schematic was easy enough; the challenge was fitting all the components into a very specific size PCB. The SEN55 took up about 45% of the available space, leaving very little room for the other components. Once I realized my desired size could not accommodate all my parts, I decided to introduce a secondary PCB to the design.

The idea was to use the inevitable height that the SEN55 module would take up to still maintain a reasonable device size. The secondary PCB would be connected to the main PCB via a flexible PCB. The secondary PCB holds two additional sensors, the CO sensor and the NO2 sensor mentioned in Vlog 4. This board also contains additional circuitry for connecting an alternative way to power the logger in the future, like a solar panel. This board generally contains things that I consider add-ons and not essential to the logger's functionality.

Once the new logger was put together, after implementing some of the solutions mentioned in the video, it was time to test the device's practicality as a whole. This is unfortunately where the logger fell short. All the electronic functions work as intended, but the physical design of the logger is not yet where I want it to be.

The idea of magnetic mounting, although sensible in concept, has only added bulk to the logger. While the mechanism works, the magnetic field produced is not strong enough to securely attach the logger. To keep this design, I will have to redesign the mechanism and also use stronger and bigger magnets to achieve the necessary attraction force.

The simpler solution is, not surprisingly, the better option here, and that's simply to use an array of non-switchable magnets attached directly to the main unit. This should significantly cut down on the size and complexity of the logger.

The other part of the logger that requires iteration is the overall PCB design and size. While I am quite happy with how small the new logger will be once the magnet switches have been removed, I will be updating the design to get the logger down to its final size.

Summary

The current iteration of the mobile logger has been utilized to collect air quality readings in select places around Lagos. Although it is not quite street-ready yet, it is a valuable addition to a journey that, hopefully, will lead us to what I believe will be the most portable air quality sensor network ever created. The goal remains to establish an air-quality network in Lagos State based on sensors that are easy to manufacture and quick to distribute.