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Our pals at Design News have an awesome "Gadget Freak: Backyard Barbeque Bonanza" with 4 projects (all with full build instructions) -

Air Conditioned Tent
Be a happy camper and stay cool as a cucumber in the sweltering heat! This portable cooling device ensures complete climate control in even the most humble of tents. Plus an optional motion sensor discourages both curious neighbors and hungry bears.

Model Rocket Launcher
What's cooler than launching model rockets? Putting on an entire air show, of course! By allowing you to sequence your launches to the tune of Yankee Doodle Dandy and more, this device is your ticket to the best backyard show this season. Guaranteed.

Model Rocket Altimeter
Fly high this summer, or at least know how high your model rockets are flying with this battery-powered model rocket altimeter. Cheap enough for even "risky" launches, thrill and amaze your friends with your NASA-like computational abilities.

Skateboard Speedometer
Kickflips and rock fakies are so pedestrian. Show your friends how really cool you are by calculating your speed, miles, and other parameters with your own DIY skateboard speedometer. Warning: Given the slight imbalance created by the magnet, the only thing you'll need to compute is a quick fix for road rage! Get Build Instructions "

Gadget Freak: Backyard Barbeque Bonanza II - Link.