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NASA style outdoor countdown clock

My problem;  as a father of two young girls, for years I have joked about getting NASA's countdown clock and placing it on our yard when they begin to date.  And start cleaning my largest guns when the clock hits @ 15 minutes or so.  Originally I thought this would be cost prohibitive- I mean, the thing is huge, and they used tax dollars to pay for it, so how cheap could it be?  Reading online about it today, I see it's been in use since the Apollo days, and it uses 40 watt bulbs, so I'm thinking (pardon the pun here), it can't be rocket science.  I don't need this to be in scale, but Id like something view able from the street, rather than a kitchen timer kind of thing.  And while I'm handy with a skill saw, I'm more of a car guy than a computer geek, so I don't even know where to start.  Ideally, I guess Id like the numbers somewhere around 12" or so, maybe larger.  Any thoughts, or experience?  The oldest starts dating in less than a week... 

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