A Portable Alarm System
While a bag stuffed with a power source and a bunch of black and red cables might be suspicious at the airport check-in, the Alarm Bag project is, in fact, extremely educational! It's an excellent lesson in designing and building a project from parts not normally used for this purpose. In other words, it's about considering possible uses of the components involved, above and beyond those suggested by the manufacturer. It's about getting creative with your hardware!
The Alarmed Messenger Bag
Like most alarm systems, this one requires specific steps to be performed, in sequence, in order to properly set the alarm. Otherwise you run the risk of triggering the diminutive but powerful Piezo siren. At 102dB, that thing is a screecher! So while you might think to plug in the external jack last, you actually want to plug this in first, then remove the internal jack. And of course, the alarm system doesn't need to be confined to a messenger bag. It could be easily reconfigured as a window or door trip, classic alarm style! If you come up with any other clever uses for the alarm or for wiring two audio jacks in series in an equally unorthodox fashion, send us an email
with your ideas.
A Little Bit More About Diodes
A couple of newsletters back, we introduced you to the rectifier diode, whose unique function only allows electricity to flow in one direction. Well, up to a certain limit, that is. And thankfully, there are spec sheets online like this one, which rates the 1N4004 diode we used in the Solar TV Remote
up to 400V of "repetitive reverse," or Peak Inverse Voltage (PIV). This is the value at which electricity will start to flow backwards, a phenomenon known as breakdown, which typically will permanently damage your device. We sure hope a PIV of 400V is plenty for most of you Weekend Project makers out there!
Resistor Color Wheel
Reading resistor values can be a bit tricky, but that's why there's an electronic color code. A color wheel calculator is a fun way to calculate a resistor's values: digit, digit, multiplier, (space), tolerance. Remember that the first three bands will always be spaced equidistant from each other; the fourth band (tolerance) will have a noticeable gap between it and the third band. There are printable versions of this wheel online, or check out this nifty interactive HTML5 resistor calculator – just spin the wheels with your mouse to calculate your colors!
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