Published July 10, 2026 © GPL3+

CO₂ Ampel Stick – Gadget for Monitoring Indoor Air Quality

The CO₂ Ampel Stick is a compact desktop monitor to continuously measures CO₂ concentration, temperature and humidity.

BeginnerShowcase (no instructions)2 hours43

CO₂ Ampel Stick – Gadget for Monitoring Indoor Air Quality

Things used in this project

Hardware components

M5Stack M5StickC ESP32-PICO Mini IoT Development Board

M5Stack UNIT CO2

Software apps and online services

M5Stack UIFlow 2.0

Story

The CO₂ Ampel (= Traffic Light) Stick is a small device that displays three essential environmental parameters at once: CO₂ concentration (C), temperature (T), and humidity (H). With its intuitive interface and traffic‑light color system, it allows users to assess indoor air quality at a glance — perfect for offices.

CO₂ concentration is a key indicator of air quality. As levels rise, concentration and cognitive performance decrease, fatigue increases, and the risk of aerosol exposure grows. The simple color‑coded feedback — green, yellow, red — makes it immediately clear when it’s time to ventilate.

At the heart of the project is the M5StickC, a compact microcontroller from the M5Stack family. It offers:

a built‑in display
small form factor
battery operation
flexible expansion options

Programming is done using UIFlow 2.0, a graphical development environment that is especially beginner‑friendly. With drag‑and‑drop blocks, the logic can be implemented quickly without writing complex code.

The M5Stack Unit CO2 sensor provides all relevant environmental data. This makes it ideal for monitoring indoor air quality in real time. The CO₂ concentration is visualized using a clear color system:

Green – good air quality
Yellow – elevated levels, ventilation recommended
Red – poor air quality, ventilation necessary

This intuitive display makes the device easy to understand even for non‑technical users.

Another useful improvement for the CO₂ Ampel Stick would be an intelligent power‑saving feature when running solely on battery. After a certain period of operation, the display brightness could automatically be reduced to significantly lower energy consumption and extend battery life. Optionally, the brightness could even be adjusted dynamically based on the CO₂ status or the remaining battery level to achieve an optimal balance between visibility and energy savings.

Code

co2-ampel-stick.py

import os, sys, io
import M5
from M5 import *
from unit import CO2Unit
import m5utils
import time
from hardware import Pin
from hardware import I2C



TITLE = None
STATUS = None
BATTERY = None
CONCENTRATION_VALUE = None
TEMPERATURE_VALUE = None
HUMIDITY_VALUE = None
HUMIDITY_BAR = None
TEMPERATURE_BAR = None
CONCENTRATION_BAR = None
TEMPERATURE_TEXT = None
CONCENTRATION_TEXT = None
HUMIDITY_TEXT = None
i2c0 = None
co2_0 = None


concentration_value = None
humidity_value = None
temperature_value = None
concentration_bar = None
humidity_bar = None
temperature_bar = None
power_mode = None
screen_brightness = None

# get and show concentration as value and bar
def Show_Concentration_Value_and_Bar():
  global concentration_value, humidity_value, temperature_value, concentration_bar, humidity_bar, temperature_bar, power_mode, screen_brightness, TITLE, STATUS, BATTERY, CONCENTRATION_VALUE, TEMPERATURE_VALUE, HUMIDITY_VALUE, HUMIDITY_BAR, TEMPERATURE_BAR, CONCENTRATION_BAR, TEMPERATURE_TEXT, CONCENTRATION_TEXT, HUMIDITY_TEXT, i2c0, co2_0
  concentration_value = int(co2_0.co2)
  concentration_bar = int(m5utils.remap(concentration_value, 300, 2100, 0, 135))
  CONCENTRATION_VALUE.setText(str(concentration_value))
  CONCENTRATION_BAR.setSize(w=concentration_bar, h=20)
  if concentration_value < 800:
    CONCENTRATION_BAR.setColor(color=0x33cc00, fill_c=0x33cc00)
  if concentration_value >= 800 and concentration_value < 1000:
    CONCENTRATION_BAR.setColor(color=0x66ff99, fill_c=0x66ff99)
  if concentration_value >= 1000 and concentration_value < 1400:
    CONCENTRATION_BAR.setColor(color=0xffff00, fill_c=0xffff00)
  if concentration_value >= 1400:
    CONCENTRATION_BAR.setColor(color=0xff0000, fill_c=0xff0000)

# get and show humidity as value and bar
def Show_Humidity_Value_and_Bar():
  global concentration_value, humidity_value, temperature_value, concentration_bar, humidity_bar, temperature_bar, power_mode, screen_brightness, TITLE, STATUS, BATTERY, CONCENTRATION_VALUE, TEMPERATURE_VALUE, HUMIDITY_VALUE, HUMIDITY_BAR, TEMPERATURE_BAR, CONCENTRATION_BAR, TEMPERATURE_TEXT, CONCENTRATION_TEXT, HUMIDITY_TEXT, i2c0, co2_0
  humidity_value = int(co2_0.humidity)
  humidity_bar = int(m5utils.remap(humidity_value, 0, 100, 0, 135))
  HUMIDITY_VALUE.setText(str(humidity_value))
  HUMIDITY_BAR.setSize(w=humidity_bar, h=20)

# get and show temperature as value and bar
def Show_Temperature_Value_and_Bar():
  global concentration_value, humidity_value, temperature_value, concentration_bar, humidity_bar, temperature_bar, power_mode, screen_brightness, TITLE, STATUS, BATTERY, CONCENTRATION_VALUE, TEMPERATURE_VALUE, HUMIDITY_VALUE, HUMIDITY_BAR, TEMPERATURE_BAR, CONCENTRATION_BAR, TEMPERATURE_TEXT, CONCENTRATION_TEXT, HUMIDITY_TEXT, i2c0, co2_0
  temperature_value = int(co2_0.temperature)
  temperature_bar = int(m5utils.remap(temperature_value, 0, 100, 0, 135))
  TEMPERATURE_VALUE.setText(str(temperature_value))
  TEMPERATURE_BAR.setSize(w=temperature_bar, h=20)

# Describe this function...
def Show_Battery_Voltage_and_Capacity():
  global concentration_value, humidity_value, temperature_value, concentration_bar, humidity_bar, temperature_bar, power_mode, screen_brightness, TITLE, STATUS, BATTERY, CONCENTRATION_VALUE, TEMPERATURE_VALUE, HUMIDITY_VALUE, HUMIDITY_BAR, TEMPERATURE_BAR, CONCENTRATION_BAR, TEMPERATURE_TEXT, CONCENTRATION_TEXT, HUMIDITY_TEXT, i2c0, co2_0
  STATUS.setText(str((str((Power.getBatteryVoltage())) + str('mV'))))
  BATTERY.setText(str((str((Power.getBatteryLevel())) + str('%'))))


def setup():
  global TITLE, STATUS, BATTERY, CONCENTRATION_VALUE, TEMPERATURE_VALUE, HUMIDITY_VALUE, HUMIDITY_BAR, TEMPERATURE_BAR, CONCENTRATION_BAR, TEMPERATURE_TEXT, CONCENTRATION_TEXT, HUMIDITY_TEXT, i2c0, co2_0, concentration_value, humidity_value, temperature_value, concentration_bar, humidity_bar, temperature_bar, power_mode, screen_brightness

  M5.begin()
  Widgets.setRotation(0)
  Widgets.fillScreen(0x000000)
  TITLE = Widgets.Title("CO2 Ampel", 13, 0xffffff, 0x000000, Widgets.FONTS.Montserrat18)
  STATUS = Widgets.Label("0000mV", 78, 220, 1.0, 0xffffff, 0x000000, Widgets.FONTS.Montserrat12)
  BATTERY = Widgets.Label("000%", 5, 220, 1.0, 0xffffff, 0x000000, Widgets.FONTS.Montserrat12)
  CONCENTRATION_VALUE = Widgets.Label("0", 30, 35, 1.0, 0xffffff, 0x000000, Widgets.FONTS.Montserrat18)
  TEMPERATURE_VALUE = Widgets.Label("0", 30, 95, 1.0, 0xffffff, 0x000000, Widgets.FONTS.Montserrat18)
  HUMIDITY_VALUE = Widgets.Label("0", 30, 155, 1.0, 0xffffff, 0x000000, Widgets.FONTS.Montserrat18)
  HUMIDITY_BAR = Widgets.Rectangle(0, 180, 135, 20, 0x0025ff, 0x0025ff)
  TEMPERATURE_BAR = Widgets.Rectangle(0, 120, 135, 20, 0xf705ec, 0xf705ec)
  CONCENTRATION_BAR = Widgets.Rectangle(0, 60, 135, 20, 0xffffff, 0xffffff)
  TEMPERATURE_TEXT = Widgets.Label("T:", 5, 95, 1.0, 0xffffff, 0x000000, Widgets.FONTS.Montserrat18)
  CONCENTRATION_TEXT = Widgets.Label("C:", 5, 35, 1.0, 0xffffff, 0x000000, Widgets.FONTS.Montserrat18)
  HUMIDITY_TEXT = Widgets.Label("H:", 5, 155, 1.0, 0xffffff, 0x000000, Widgets.FONTS.Montserrat18)

  power_mode = False
  screen_brightness = 10
  Widgets.setBrightness(screen_brightness)
  i2c0 = I2C(0, scl=Pin(33), sda=Pin(32), freq=100000)
  co2_0 = CO2Unit(i2c0)
  co2_0.set_stop_periodic_measurement()
  co2_0.set_factory_reset()
  co2_0.set_start_periodic_measurement()
  while not (co2_0.is_data_ready()):
    time.sleep_ms(100)
  Show_Concentration_Value_and_Bar()
  Show_Temperature_Value_and_Bar()
  Show_Humidity_Value_and_Bar()
  Show_Battery_Voltage_and_Capacity()


def loop():
  global TITLE, STATUS, BATTERY, CONCENTRATION_VALUE, TEMPERATURE_VALUE, HUMIDITY_VALUE, HUMIDITY_BAR, TEMPERATURE_BAR, CONCENTRATION_BAR, TEMPERATURE_TEXT, CONCENTRATION_TEXT, HUMIDITY_TEXT, i2c0, co2_0, concentration_value, humidity_value, temperature_value, concentration_bar, humidity_bar, temperature_bar, power_mode, screen_brightness
  M5.update()
  if co2_0.is_data_ready():
    Show_Concentration_Value_and_Bar()
    Show_Temperature_Value_and_Bar()
    Show_Humidity_Value_and_Bar()
  Show_Battery_Voltage_and_Capacity()
  time.sleep(15)


if __name__ == '__main__':
  try:
    setup()
    while True:
      loop()
  except (Exception, KeyboardInterrupt) as e:
    try:
      from utility import print_error_msg
      print_error_msg(e)
    except ImportError:
      print("please update to latest firmware")

Credits

esferatec

2 projects • 0 followers

CO₂ Ampel Stick – Gadget for Monitoring Indoor Air Quality

Things used in this project

Hardware components

Software apps and online services

Story

Schematics

setup block

loop block

concentration function

temperature function

humidity function

battery function

Code

co2-ampel-stick.py

Credits

esferatec

Comments

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CO₂ Ampel Stick – Gadget for Monitoring Indoor Air Quality

CO₂ Ampel Stick – Gadget for Monitoring Indoor Air Quality

Things used in this project

Hardware components

Software apps and online services

Story

Schematics

setup block

loop block

concentration function

temperature function

humidity function

battery function

Code

co2-ampel-stick.py

Credits

esferatec

Comments

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