The SCO2 is a small scale personal initiative to create CO2 sensors for the school my kids go to. Goal is to make the sensor:

• Easy to use for teachers and kids
• Show details for those interested
• Looks good draws attention when needed
• Solid to survive the challenging school environment
• Decent but relatively cheap to build

The first version is a completely home made device using some electronics, a soldering iron and a 3D printer (or an online 3D ordering service).

The following components are used to build the sensor:

• Wemos D1 Mini ESP board (this is the computer) https://www.wemos.cc/en/latest/d1/d1_mini.html
• Sensirion SCD30 (This is the CO2 / Temp / Humidity sensor) https://www.sensirion.com/en/environmental-sensors/carbon-dioxide-sensors/carbon-dioxide-sensors-co2/
• Wemos TGB Led Shield (to coler indicate air quality) https://www.wemos.cc/en/latest/d1_mini_shield/rgb_led.html
• Some wires, shrinking tube and screws
• 3D model existing out of 5 parts to put the sensor together. I fiddled around a bit with the tolerances to make the parts fit together nicely, so you might need to do so too.

I started out programming the thing myself in Visual code, that gives me great abilities but also is quite cumber stone since I'm not a programmer by trade. So I switched to ESPhome (https://esphome.io/). ESP Home abstracts the actual programming for you and all you need is a configuration file to tell the system what to compile for you. It can be ran alone or integrated into Home Assistant if you want an easy and comprehensive overview of all the sensors in for example your school.

To be clear, the device can run alone without WiFi of back-end, but when you're up for it you can connect it and save the data in various systems.

The device exists out of 5 3D printer parts you can print on your own printer of via a service. You find the here, and assembling should be possible in one way only. :)

Maybe I'll create a visual guide one day, but for now: The hardware assembly consists out of 2 part, the D1 mini in the foot of the unit, and the sensor array holding the CO2 sensor and the LEDs. I build it like this so we can create new sensor array's later on and just swap them out.

This is the easy part, just solder a MALE pin header strip on the board ON ONE SIDE ONLY. We're only using the side of the board with the pin headers 5V to TX. once done, use 2 small screws to screw the board in the 3D printed bottom plate.

This is a bit trickier, since we need some wire and a couple of more connections. You need to:

• 5V pin to 5V on the CO2 sensor and 5V on the LEDs
• GND pin to GND on the CO2 sensor and GND on the LEDs
• D4 on the board to D4 on the LEDs
• D2 on the board to SDA on the CO2 sensor
• D1 on the board to SCL on the CO2 sensor

When you have all the parts in house and printed the enclosure make sure you have ESPHome running. For me it's part of my Home Assistant installation and for the school I build this for I have a Raspberry PI where I run HASSOS with ESP Home in. To get HASSIO running, please find the software and instructions here: https://www.home-assistant.io/installation/ .

When you have ESPHome running as a Add-on:

• Open the ESPHome interface
• Connect the Device with a USB cable to your HA device
• Open the "Secrets" File in the rop right corner to enter your passwords you will use (example in this github called secrets.yaml)
• Create a new device, give it the right name straight away, but the rest of the information can be bogus IF you are using exactly the same ESP board
• Now change the interface to upload the code to your device from over the air to the USB port (you can use OtA after initial flash)
• Once created open the config by clicking "Edit" and past the example config from the repo into you config (sensor.yaml).
• check if all the password and config options are correct and upload the file with "Upload"
• See what happens.
• You can add the sensors to HA if you want under Integrations or under Device.

Cheers! Drop me comments or improvements here in GitHub please.

• Home Assistant for building great software that makes this easy to run a OS and a great Add-on ->
• ESPHOME! This is amazing. Next gen programming language to make IOT easy IMHO.
• Autodesk for having a free edition of Fusion360
• Ultimaker for providing the best slicer software for free to slice the 3D design and print them.