• Credits
• General information
• Used parts and components
• Circuit diagram
• License

First things first, I didn't create this project on my own. It was planned and built in a German workshop for young technicians by our instructor (who 3D-printed the housing and wrote the basic software) and a handfull of electronic and mechatronic trainees, including me. The jobs that I did only were soldering the PCBs and overwriting the software, so please don't praise only me, if you even want to.

If you want to know more about this workshop, visit their website (German).

As you hopefully already noticed, the microcontroller for this project is a ESP8266 running the operating system NodeMCU. As it is programable via the Arduino IDE, we'd choose it for the CO2-sensor project. If you want to use the software for your own sensor and choose a different µC, don't forget to update the software.

Powering. The circuit is getting powered through a tiny hole on the side of the housing, were the Micro-USB port of the µC is located. The power for all external compenents is served through that port, so you won't need a second power supply. Please note that the ESP8266 only serves 3,3 Volts on its power pins. As the MHZ19B sensor has an operating volate of 5 Volts, it gets powered through the V_in pin of the µC.
Note that you can't power this circuit via your PCs USB port. Because of.. high power consumption thingy..

LEDs. When using LEDs in circuits, always be sure to calculate the current limiting resistor properly.
R_RESISTOR = ( U_OUT - U_LED ) / I_MAX
U_OUT = 3,3V
U_LED ≈ 2V (Insert the nominal voltage of your LED)
I_MAX = 10mA

Other components. Perforated boards, dupon cables, hot glue and some basic electronic tools.

Notes. If your piezo buzzer has a nominal current flow that is higher then the digital pin I_OUT, you need to limit the current with a resistor.
Also, this circuit diagram was made using Microsoft Paint and Microsoft Excel. Again, please don't hit me.

This repository is covered by the GNU General Public License 3.