Maker "rabbitcreek" has published a wall-mounted carbon dioxide meter with a difference: the recorded measurement swings an oversized analog needle around, corresponding to the parts per million (PPM) CO₂ detected.
"The current atmosphere above a mountain in Hawaii contains about 400 PPM of carbon dioxide. This number is extremely important to all that live on the planets surface. We are surrounded now by either deniers of this worry or those who wring their hands in a flurry of agitated concern," explains rabbitcreek of the inspiration behind the project. "But this number and the thousands of numbers that follow it in the news are hard to really comprehend on a daily basis. What is the amount of CO2 around me? How can I relate to this idea of gasses in the atmosphere causing overheating of the planet?
"For those interested I have built a Giant Analog CO₂ meter that with the help of a four foot long needle will enliven this discussion of any school room or museum on how CO₂ is measured and how you can become a part of this gas analysis."
The 'analog' portion refers, of course, to the action of the needle, which like panel metres of old swings to and fro to indicate changes in measurements — though at four feet long its movement is a little more dramatic than most. The actual sensing is carried out by a Sandbox Electronics MH-Z16 CO₂ sensor - good to 10,000 parts per million — connected to an Adafruit Feather 32U4 microcontroller and 2.13" three-color e-paper display. The motion of the needle, meanwhile, is provided by a digital servo.
The needle isn't the only eye-catching part of rabbitcreek's design, either: the electronics are all housed in a 3D-printed chassis designed to look like a nautilus shell, with mounts for the needle to swing and a cut-out for the low-power display. The software is a relatively simple Arduino sketch — "the only tricky part," rabbitcreek warns, "is limiting your servo range so it doesn't bang into the sides of the mount."
The full build guide, along with bill of materials, STL files for the chassis, and Arduino sketch, are available on rabbitcreek's project page.