avipami:
Thank you for the tip ! I can think about the wireless later on but the most important question
for my project is how can I make a board become like a mirror to the other one ?
Not really implementing a master/slave mode but having both boards react the same and together,
You need a bit of lateral thinking.
Establishing a master-slave relationship between the wireless devices does not prevent the boards from mirroring each other.
The master-slave arrangement is just to make the wireless easy. The master sends data to the slave (say 10 times per second) and the slave sends data back. Using that data both boards can adjust themselves to match the other aspects of each other.
What you really need to think about is the logic of your system. Consider a simple system in which both boards have an LED and a momentary push-switch. Let's start with both LEDs off. Suppose ButtonA (the button on board A) is pressed. Then LedA lights and a message is sent to boardB telling it that ButtonA has been pressed and that LedB needs to be turned on. ButtonB has not been pressed so boardB sends back that information. Later ButtonB is pressed and LedB is turned off and when boardA (acting as Master) sends a message that buttonA has not been pressed boardB will respond with a message saying ButtonB was pressed so boardA knows to turn off LedA
...R