Recently saw several interesting projects
this project is based on arduino pro micro, I am more interested in him based on qmk firmware
https://hackaday.io/project/163491-yampad-feature-packed-open-source- macropad # menu-description
This is stm32f103 do, the cost will be lower a lot
https://hackaday.com/2019/03/19/venabili-is-the-delightful-keyboard-you-cant-buy/
This is github address
https: // github.com/alx741/venabili/tree/master/src
This is not bad, seem to be able to arduino under the code
https://www.kickstarter.com/projects/jacoburge/touchpad-the-arduino-compatible-customisable-keybo
Reproduced in: https: //www.jianshu.com/p/fb11be5ffaf7