What is it?
A KiCad PCB project plus firmware for a portable CO2 sensor based on the WCH CH32X033 MCU. This is my first PCB with this chip and so far it's impressing me quite a bit. I was able to buy a small quantity for about 23 cents each. The 033 is part of the CH32X035 family and has a 48Mhz RISC-V core with 20K SRAM, 62K FLASH, USB full speed and many of the typical I/O capabilities of 32-bit MCUs. This project was more of an experiment to see if I could easily add some USB functionality to my battery powered CO2 sensor.
What's special about this project?
By using a low cost display, MCU and sensor, my aim for this project was to make a practical and low cost way to carry a true CO2 sensor in your pocket. The CH32X033 also allowed me to easily add USB CDC support so that a PC could receive the sensor readings too. I use a clever single pushbutton circuit to control power and input. By using the enable pin of the 3.3v regulator in software control, the device can turn itself off. I use this feature to make sure the battery isn't accidentally left for dead. After 5 minutes of use, it will turn itself off.
Building the Project
I used KiCad to design the PCB and all of the source files and Gerber zip is in the PCB folder ready to send for production. I assembled the board myself, so I don't have any assembly instructions/files with it. The firmware was built using MounRiver Studio IDE and the CH32X035 EVT provided on the WCH website.
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