32u2 minimum system

The minimum system of atmega32u2.
It can be used for customized keyboards.
It provides electrostatic protection, overvoltage protection, anti-reverse connection, etc.
The reason for the production is that the price of atmega32u4 is too magical.
Advantages: Extremely compressed volume, but does not use the devil package that humans cannot weld. It uses 0402 package, single-sided patch, significantly improves welding efficiency, facilitates welding on the welding table, reduces welding difficulty, reduces height, and the minimum version is only the size of a coin.
There are multiple versions, please use them according to your needs, but please do not use version 1.5 because it has bugs.
Provide two-pin crystal oscillator and four-corner crystal oscillator versions, pay attention to distinguish.
Please be sure to read the schematic in advance!
This project can be used commercially, but be sure to indicate the project address.
Except for 1.5, all versions have been tested and passed, and the cost is about 35.
It is for learning only, and any consequences are at your own risk.