Tear Down: Simple, Inexpensive CO2 Sensing Device
April 26, 2022
The CO2GO is a mobile CO2 sensor that’s simple to use and sells for about $130. Built around the Infineon Xensiv PAS CO2 sensor, the system contains green, yellow, and red LEDs that reflect the ambient air quality. Since it’s USB-powered and weighs just a few ounces, the CO2GO can be plugged into a wall charger, computer, and used just about anywhere.
The CO2GO sensor system is accompanied by a desktop and smartphone app with a real-time “CO2-o-meter” that provides much more granular detail about CO2 emissions than the onboard LEDs. This information includes specifics about various CO2 levels, when you should be concerned, and tips on what to do if levels become dangerous. It also charts levels over time, showing the maximum and minimum readings for each session. These results can be exported as a .csv file for further analysis in the future.
Even though my CO2GO — post Tear Down — is in multiple pieces, it’s still functioning and runs full time in my office. I use the desktop app (shown in Figure 2), and so far, so good for me and my office.
Figure 2. The CO2GO app displays, amongst other things, the amount of CO2 that’s present in the room.
The brain of the CO2GO is an Infineon Xensiv photoacoustic spectroscopy (PAS) CO2 sensor, seen in Figure 3.
Figure 3. The heart of the CO2GO CO2 sensor is the Infineon Xensiv PAS CO2 sensor, found on the module in the metal can.
The Xensiv PAS CO2 sensor is a relatively simplistic device. In use, the CO2 that’s present emits a resonance; the sensor excites that resonance and measures it. It measures the content of CO2 that gets trapped in a particle area at an accuracy ±30 PPM.
The sensor module contains four components, with the CO2 sensor being the main one. There’s also an Arm Cortex-M0-based Infineon MCU and some voltage-regulators. The MCU, along with a USB bridge, provides an interface to the host device.
The sensor module also controls the three LEDs, a green, a yellow, and a red. In safe conditions the green LED will remain lit. If a certain level is exceeded, the yellow LED will illuminate, warning the user that the level is rising, and potentially nearing a dangerous situation. You can probably guess what the red LED means.
“This technology results in a better accuracy compared to some of the incumbent technologies like nondispersive infrared (NDIR) or electro-mechanical or any of the older technologies,” says Kim Lee, a Senior Director of System Applications Engineering at Infineon. “That allows us to package the sensor in a very small form factor, apply some intelligence and bundle it into a module.”
Infineon was deeply involved with the CO2GO design team, offering design suggestions along the way. They helped with the power subsystem, ensuring that it ran as optimally as possible. They also assisted with some of the software writing. They were not involved in the industrial design which, frankly, is quite cool.
If you’re bold enough to break yours down, a configuration that’s not currently available from CO2GO but could easily be designed in is a Bluetooth version of the device. You could just replace the USB circuitry with a Bluetooth transceiver, but you’d also have to include a battery and a way to charge it.
I’m not sure if that one is on the drawing board, but wouldn’t be surprised to see one soon.