1.54 double-layer plug-in board - motherboard

• Thanks to Lichuang user @1174247739lc for providing ideas!
• The functional hardware is basically the same as that of Duck.
• By adding the lower layer, functions such as ink screen access control keychain, portable small calendar, photo decoration, etc. can be realized.
• The motherboard can use esp8266, msp430, stm, etc. All can be replaced to expand playability .
• 2.00mm pins are used instead of the commonly used 2.54mm, because 2.00mm is shorter and takes up less space.
• There is no built-in burning module, because except for debugging, in practice, burning is rarely needed and can be solved with OTA. However, the Xianneng burning port is still used for burning, and it can be burned with just one clip, which is very convenient. It saves costs, reduces welding volume and reduces welding difficulty.
• Using HT7833, theoretically no tantalum capacitor is needed, but the position of the tantalum capacitor is still retained.
• Use Type-c.
• esp12s is compatible with esp12e etc.
• Thanks to Weixue wiki.
• Regarding the source code, there will be some, and open source is supported. Pay tribute to the big guys who are active in open source!

I'll try to answer all your questions as best I can, thanks for the comments!