This is the (rather trivial) code for a simple LED-based CO₂ light meter (more or less a continuous CO₂ "traffic light") based on the following hardware components:

• A Raspberry Pi or similar single board computer (SBC) with a 40-pin GPIO bar. In my case I first used an older Raspberry Pi 2B with an matte-black Pibow Midnight (Coupé) case which I bought in 2017 from Pimoroni. Later I used a Raspberry Pi Zero H with a 8086 Solderless Zero Dongle to be able to use it like a USB stick.

• The Pimoroni LED Shim as LED bar.

• The Pimoroni SCD41 CO₂ Sensor Breakout as CO₂ sensor.

• One of following as socket for the CO₂ Sensor Breakout:

  • the Pimoroni Breakout Garden Mini (I2C) pHAT,

  • the Pimoroni Breakout Garden Mini (I2C+SPI) pHAT, or

  • the bigger Pimoroni Breakout Garden HAT.

• Optionally, if used with a fullsize Raspberry Pi, the Waveshare Raspberry Pi 400 GPIO Header Adapter to on the one hand turn the pHAT or HAT vertical (so I don't have to setup the Raspberry Pi vertically) and on the other hand allow to mount the LED Shim even if a case is used which encloses the GPIO pins to some height.

• Optionally, if used with a Raspberry Pi Zero, either

  • the more recent Solderless Zero Dongle by 8086.net, or

  • the original ZeroStem which requires some soldering, but is more compact and still allows to attach a keyboard. (Also available at e.g. Pimoroni.)

The code in here is heavily based on two example scripts from Pimoroni's LED Shim and SCD4x Python libraries (which are needed anyways, too), namely on:

• scd4x-python/examples/basic.py
• led-shim/examples/gradient_graph.py

Since the code is heavily based on two scripts published under the MIT License, this code is licensed under the MIT License as well.

• Copyright 2017, 2018 Pimoroni Ltd.
• Copyright 2022 Axel Beckert