My brother use to have a book (well, probably still does somewhere) called The New Way Things Work. It had simple explanations of how tons of different mechanisms work, but it had an entire chapter dedicated to explaining how digital systems could work, using woolly mammoths and various sorts of pie transportation devices. Really brilliant and detailed illustrations throughout.

I have always thought it was a wonderfully delightful way to introduce children to those sort of concepts. It was more EE/CE than coding (and the rest of the book was heavily ME), but I think the approach adapts to coding equally well.

(http://www.amazon.com/The-New-Way-Things-Work/dp/0395938473)

The Way Things Work by David Macaulay. The way it mixes comic illustration, simplified explanation of everyday things, and fictional narrative is deeply engaging to curious minds but also very forgiving of a child's fickle attention. I'm within arm's reach of the copy I was given almost twenty years ago.

http://www.amazon.com/New-Way-Things-Work/dp/0395938473

He might like David Macaulay's _The Way Things Work_ ( http://www.amazon.com/New-Way-Things-Work/dp/0395938473/ ).

Also, libraries in general, including university libraries. Some books on homeschooling (such as Grace Llewellyn's _Teenage Liberation Handbook_) are full of pointers for self-study.