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Working with relays

relay

SparkFun’s latest tutorial shows you how to work with relays. A relay is an electrically operated switch. In this case, they’re using it to switch a 120V AC outlet. The article carries the standard warnings about how not to kill yourself with AC (plus some non sequitor linking throughout). As an extra precaution, they chose a GFI outlet. You probably know how a relay works, but it’s worth seeing how they implemented it. They use a transistor to prevent overloading the microcontroller’s GPIO pin. The control pin is pulled to ground to keep the relay off. A diode is placed across the relay coil to manage the power flow when it discharges. An indicator LED is included to show when the relay closes. This is a great foundation for an automation project, or maybe you just want to terrorize your cat.

Kill A Watt teardown

killawatt

Come on, folks. If we keep tearing apart everything that’s handed to us, we’ll never get nice things. SparkFun got their mitts on two Kill A Watts and proceeded to plug them into everything and then dismantled them to see how they work. The Kill A Watt keeps track of how much power is used over time. The largest load they found was their soda machine using 500W (should probably add a motion sensor to that). They plugged a meter on either side of a UPS and found out that it uses 5W just to charge. On the inside of the meter, there isn’t anything too substantial. One unlabeled IC runs the whole show.

Tesla coil tuner


Here’s one more use for the insanely handy LM555 chips. [Terry] put together a Tesla coil tuner around one. The 555 is used to generate a range of frequencies while a simple double LED arrangement indicates the presence of an output spike from a coil due to the resonance.

Maker Faire 2008: Electric motorcycles


Builder [Justin Gray] brought a pair of electric motorcycles to Maker Faire last weekend. Pictured above is the R84, which has 28 LiFePo cells and an 84v AC induction drive providing 54HP. All of that is stuffed in a 2000 Yamaha R1 frame. You can buy it now for $14,000.

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