Thanks for your reply. As a matter of fact, my intention about the Led turn it on and off doing a fade in/out effect, like a dimmer. At the same time the FX sound is played. That's why I need the mini Arduino board. Those are the internal dimensions available for this project:
Grip Top Box (Bordeaux part) is 112mm x 38mm x 15mm (L,H,W)
Grip Handle (Mustard part) is 39mm x 95mm x 19mm (L,H,W)
Need space for a battery pack and for one mini speaker as well.