While at first I had hoped this project to be every child's 'next step' type of project from just working on the Pi alone, or adding a few 'canned sensors', and though the general 'Hack-a-Day' community/audience does tend to be 'generally mature', it has come to my attention that if you fancy yourself a 'young hacker', for one, in the previous step, yes, 'DON'T BREATHE IN THE FIBERGLASS DUST', just carefully lean the board over and blow it out like 'fairy dust' into the trash.

On the net, I have seen some people wearing surgical gloves at this step, but that simply is 'too much', as long as you are careful and gentle with your etching it is really not that kind of scenario.

However, the 'next step' does require some 'adult' supervision-- Or, if you are a really clever kid, basically what we are dealing with here is some variation the game 'Battleship!', with a keyboard matrix circuit for the buttons and with that, the presumption that only one key will be pressed at any time. So thus these traces must be leading 'somewhere' and at the end point presumably to an IC for processing.... And so why all this 'nonsense' (to come), why not intercept the signal at the source and hack the IC ? Or better yet, place a very small DIP/SMT IC between the IC and the button sources to produce just the signal one wants ?

And, yes, these would all be more clean and 'advanced' solutions, if one wants to spend a great deal of time learning about 'this particular phone', but, in the end, that is not what either hacking or engineering is about.

For example, I cannot possibly imagine this phone is running some sort of ARM processor on its front end, so it is likely commodity and small.

On the other hand, the keyboard matrix layout is likely universal to any device and almost all such class of phones. Thus it is both the easiest point of access and 'most obvious' point of attack for this particular problem.

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When starting on your own design, yes, within conventions, at least whether you want it to be 'comprehensible' (or sometimes not), you are free to design as you like-- But working backwards, always look for the 'open door'. As you get more skilled in electronics you will see more of them, standard circuits, etc.

This isn't 'being lazy', rather 'building your skill set'-- And just as a 'real' example I'd 'heard' of keyboard matrices and had some understanding of how they work, but never, before this, actually played with/constructed one myself, because in the end we all have *different* areas of expertise/experience (or I am 'more comfortable' with ICs, but I just said, in this case, let's try it).