should I use capacitor between gnd & Vcc ?? how could I calibrate them?
It's always a good idea to have some. Normally a little one to get rid of high frequencies (0.1uF to 0.01uF) and a big one for the DC response like 100uF or bigger. It's not too critical, you can have too little but not too much.
- ok for linking of Gnd... BUT, how it goes? Directly on the PCB?
Any way you like, I normally run another wie from the PSU but you can link from the PCB. It's not too important as there is not a lot of current being drawn on this connection but it needs to be connected to provide a reference for the switching signals.
Seeedstudio
You remind me of my old professor
I used to be what you would probably call a professor (but in the UK professor is something rather different being a head of research at a university)
What is the difference between strict and accurate?