co2ampel

idea

higher concentrations of CO2 inside will make you sleepy and have an impact on your wellbeing. during the current pandemic higher CO2 concentrations inside are also a pretty good indication for higher levels of aerosol and as such a higher risk for infection. the 'CO2 Ampel' (CO2 traffic light) will give you a visual representation of the current situation and remind you to open windows to keep you happy and healthy

parts list

description	part	link
ESP32	ESP-32 30Pin	Aliexpress Link
Infrared CO2 Sensor	mhz-19	Aliexpress Link
Active piezzo buzzer	KY-012	Aliexpress Link
OLED Display	SSD1306
LED-Ring (9 Pixel)	WS2812	Aliexpress Link

build

• solder everything according to the connection schema
• get yourself a copy of esphome (https://esphome.io/)
• compile the firmware with co2ampel=USER_ROOM esphome co2sensor.yaml run (replace user with a nick that identifies you or your organisation and room with the place the sensor is located at - these will be used for online graphing!)
• hold boot on your esp32 until fw upload starts.

setup

• place the sensor in your room, keep it away from direct exposure of breath (give it at least 1-2m distance to humans or other co2 sources to get the average co2 level of the room)
• when there is a freifunk wifi around there is nothing to do for you, same when you defined your own wifi via secrets.yaml.
• else just wait a bit and the sensor will spawn an wifi without a password. connect with your phone and choose to login or open http://192.168.4.1 in a browser to enter your wifi credentials
• when everything is done, the default config will send the sensor readings back to the project where you can view online graphs (see grafana)

grafana

there is a quick setup on http://co2.cyber23.de:3000/d/1axlpIdGk/co2?orgId=1&refresh=10s your sensor should apper in the list on the left as soon it is connected via wifi

schema

ESP32 PIN	peripherals	note
VIN	mhz-19 (VCC)
GND	mhz-19 (GND)
GND	KY-012 (GND)	passive buzzer will do as well
D12	KY-012 (Signal/+)
3V3	SSD1306 (VCC)
3V3	WS2812 (VCC)
GND	WS2812 (GND)
GND	SSD1306 (GND)
D4	WS2812 (DI)
RX2 / D16	mhz-19 (TX)
TX2 / D17	mhz-19 (RX)
I2C SDA / D21	SSD1306 (SDA)
I2C SCL / D22	SSD1306 (SCL)

ws2812

if your ws2812 don't work on 3.3V power (most will do) you can try to use 5V instead. there are plenty different ws2812 builds so ymmv... if the leds don't work with 5V try to add a pullup resistor to your data line and a diode towards D4 to raise your high level while protecting your GPIO (https://forum.arduino.cc/index.php?topic=578735.msg3941756#msg3941756) looks like this:

either way it might be a good idea to have a capacitor between VCC and GND. my prototype worked without any of these, but from time to time some LEDs just randomly turn on...

readings for inside rooms

CO2 measure	light	buzzer	meaning
400 ppm	none	no	more or less the baseline of the sensor hardware and means 'fresh air quality'
400-800ppm	none	no	safe zone and can be considered good air quality
800-1500ppm	yellow	no	warning zone (consider to open windows) and is between medium and bad air quality
> 1500ppm	red + blink	no	bad air quality, ppl in the room will be affected in a negative way

todo

• cooldown time for buzzer (alarm only once every n minutes) -> lambda/interval/on_time?
• add openings for mh-z19 to the case
• adjust light tunnel to use frosted acrylic glass
• add a silent switch for meeting rooms and such (no buzzer, but flash at a regular interval to attract attention)