In this project, I used capacitive sensors as the input of users' gesture.
There are 5 problems in total I solved and I can imagine there still more need to consider about.
The first one is to choose the right sensor.
My first try, I used a MPR121 adafruit breakout to prototype which worked well and gave me 12 touch pads. As I order my parts all the suppliers said the sensor was retired. Fine, I shifted to an upgrade one, cap1188, which on adafruit also have a breakout can be used to prototype and works pretty good as well.
Here comes the second problem, the sensor is lead free, which means it's so tiny and no pins and only has a square GND.