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Showing posts from December, 2009

Toy decoding: vtech Push and Ride Alphabet Train

So, it's Christmas and you end up visiting people with kids... and they've got a fancy new vtech Push and Ride Alphabet Train. Now, you're the world's worst child minder because you see it and think: how does that work?


Specifically, when you insert one of the 26 alphabet blocks into the side of the train how does it know to say the correct letter? And how does it know which side (letter or word) is facing outwards (so it can say a letter or a corresponding word: "A is for Apple" etc.).

Now it quick examination shows that there are 6 small switches in each block receptacle and that each block has corresponding bits of plastic and holes to make different binary patterns. The top bit (bit 5) seems to be used to indicate which side of the block is showing.

That leaves 5 bits for the alphabet. Of course that means there are 32 possible combinations (actually 31 since 'block not present' indicated by all switches up is important), and 26 letters in the al…