The Raspberry Pi Pico has been making a lot of waves since it hit the market earlier this year. The Pico is a microcontroller development board, like the popular Arduino Uno, but it is much smaller, far more powerful, and a lot more affordable. Part of the Pico's success is a result of the RP2040 microcontroller that Raspberry Pi designed for the board. Several other boards now feature the RP2040 and you can even design your own, if you're lucky enough to find an RP2040 in stock. Guido Burger created a 3D-printed ring that uses the RP2040 to measure CO2.
The Raspberry Pi Pico's RP2040 is a desirable microcontroller, because it is very cost-effective and also one of the most powerful microcontrollers on the market. It has dual Arm Cortex-M0+ cores running at 133 MHz, 264 kB, and supports up to 16 MB of off-chip flash memory through a QSPI bus. With up to 30 GPIO pins, including four analog inputs and goodies like dedicated SPI and I2C controllers, the RP2040 is quite the package. In this case, it is probably overkill, since Burger is only using the microcontroller to read CO2 sensor readings and to drive a handful of NeoPixel LEDs. But the price of the RP2040 is comparable to many less-powerful microcontrollers, so there is no reason not to use it.
To make use of the RP2040, Burger designed a tiny development board. It resembles the Adafruit QT Py RP2040 development board, but appears to be a custom design. That small board contains the RP2040 microcontroller, a single Adafruit NeoPixel RGB LED, and a Sensirion SCD4x CO2 sensor. There is also an additional Adafruit NeoPixel Ring, with 12 RGB LEDs, which surrounds the board. Power comes from a LilyPad coin cell battery holder board, which includes a power switch. Those boards all attach to a 3D-printed ring, which looks a bit like a Ring Pop with the candy missing. Burger hasn't provided many details about the functionality, but it is safe to assume that the LEDs indicate the current CO2 readings.
We aren't sure why someone would need a wearable CO2 monitor, but this is definitely the one that we'd choose if we did find ourselves in need.