I think RapooV500AllOY is the cheapest mechanical keyboard I found on TAOBAO with not bad quality. (amazing US$15...)
I want layout new board mount on back of keyboard to replace the function of original chip , but use original circuit by touch solder point (with somthing like "Battery spring").
Layout the board is the part of my whole project. (there are a lot of task like programming with mcu...etc)
First time, I use (stm32F103 + Bluetooth Module) in test version => the Main Project Image
I decided change chip to nrf51822 (mcu & BLE stack all in one) in this project.
Now still in development... (I'm new in layout baord, so I have to learn how to use CircuitMaker)