I've re-test :
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with KEY pin (GND) & STATE pin (A0) disconnected => OK
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with KEY pin (GND) re-connected = OK
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with KEY pin (GND) & STATE pin (A0) re-connected = KO
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with KEY pin (GND) & STATE pin (another analogic pin than A0) re-connected = OK !!!
So, I don't know what's wrong with the A0 pin used as INPUT pin, but it was working and now, it doesn't work anymore, but I use A1, A2, A3... it works fine !
No idea...