Distributed LoRa based CO2 monitoring network - A standalone open source system for contagion prevention by controlled ventilation

Abstract

In the face of a global pandemic, such as that caused by the SARS-CoV-2 virus, the prevention of new infections is essential to stop the spread and ultimately return to normality. In addition to wearing masks and maintaining safe distances, regular ventilation in enclosed spaces where several people are gathered has proven to be an effective protective measure as advised by the World Health Organization. Additionally, as has been shown in a recent study of other airborne viruses, there is a strong correlation between the CO₂level and aerosol content in a confined space under the assumption humans are the only CO₂source. This can be exploited by means of a low-cost infrared CO₂sensor to indirectly monitor the aerosol content and to provide targeted ventilation if predefined thresholds are exceeded. The distributed CO₂monitoring network presented in this paper extends that idea and provides an inexpensive, comprehensive and modular monitoring network based on readily available components and 3D printing. By using a long-range communication link (LoRa) to centrally collect the real-time CO₂concentration in a multitude of rooms, this network is particularly suitable for larger building complexes such as kindergartens, schools and universities without requiring partial or even full WLAN coverage.

Keywords: 3D-Printing; CO2 monitoring network; COVID-19; Contagion prevention; General protective equipment; SARS-CoV-2.

Graphical abstract

Fig. 1

Shown is the concept of the CO₂ Monitor System. Each individual transmitter node is equipped with a display, a visual and an acoustic signal. The communication with the receiver node is done via LoRa. The receiver node additionally transmits the real-time data to a Raspberry Pi using the MQTT protocol over the Pi’s own access point, thus allowing integration into other systems.

Fig. 2

4-step instruction on how to duplicate the provided Node-RED flow CO2-Monitor-Station.json to accommodate the user interface to the required amount of CO₂ traffic lights.

Fig. 3

Wiring diagram of the CO₂ monitor.

Fig. 4

Crucial dimensions when wiring the components onto the DOT PCB. The dimensions of the shown PCB are 100 mm × 65 mm (h × w).

Fig. 5

Step-by-step wiring: connecting the CO₂ sensor.

Fig. 6

Step-by-step wiring: connecting the OLED display.

Fig. 7

Step-by-step wiring: Connecting the LoRa modul.

Fig. 8

Step-by-step wiring: connecting the RGB LED.

Fig. 9

Photograph of a) the assembled DOT PCB, b) the empty ‘casing (back)’, c) the ‘casing (front)’ with the ‘Touch plate’ wire visible and d) the completely assembled CO₂ traffic light.

Fig. 10

The presented CO₂ monitor allows simultaneous monitoring of several rooms at the same time as shown in the screenshot above. Here the CO₂ concentration, the room temperature and the received signal strength indicator of the LoRa modul are displayed i.e. for system debugging during installation.

Fig. 11

Validation of the CO₂ concentration measurement capability of the presented hardware. A total of four predefined gas mixtures were prepared. The measured static concentrations (blue) were taken after the sensor had been flushed for approx. 25 min. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 12

Validation of the CO₂ monitoring network through a field test in a school. Shown is a sketch of the classroom’s layout and the relative position between CO₂ traffic light in red and windows in blue. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 13

Validation of the CO₂ monitoring network through a field test in a school. Shown is the measured course of CO₂ concentration over 6 school hours (07:45–12:15). A gray shading corresponds to no ventilation, during a blue one there is ventilation and in the dashed areas the classroom was empty. A ventilation-dependent decrease in CO₂ concentration with an expected delay after opening the windows can be clearly seen. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 14

Validation of the CO₂ monitoring network’s LoRa capabilities according to Table 2 using a sketched layout of the school building. The red dot represents the position of the fixed receiver (connection station). The numbered blue dots show the relative positions of the transmitter (CO₂ traffic light). Distances used are estimated and differences in height are not shown in this sketch. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)