This is a fun project for which I created the UX/UI specs including controls, animations, 3 games - Snake, Breakout, Match, and a whole series of transitions and animations. They also used some of the icons for the hardware I created. Here's a link to a review of the product: https://www.youtube.com/watch?v=sJ839wIddN4
To write the specs, required an interview with the Creative Lead to discuss what they want the toy to do. My job is to take those wishes and turn them into a document that can be shared with programmers to turn it into code for the toy. The first thing I do is create a virtual prototype/mockup including the basic inputs, outputs, and modes/functions - in this case, Free Play, 3 Games, and Scripted Animation Sequences.
From there, I use what I call the 'Play Logic' method of words and pictures to describe interfaces, animations, and sequences for each mode, including introductions, game behaviors, and rewards. In this case, a demo animation for a version of the classic 'Brick Out' game is built using the existing grid of LED buttons as the interface. Some times the gameplay changes as I build the sequences and these changes are captured in the text areas of the document. The more complex the play, the longer this takes.