Elevator TARDIS

Posted on Feb 5, 2014

The core of this project (play a sound when a sensor is activated) is applicable to all sorts of areas (Halloween, art installations, scaring your little brother, Burning Man, etc. ), so read this with an eye to applications you`d like to see. My first thought was to hack straight into the elevator`s up and down buttons, but I quickly came to my senses. Building

Elevator TARDIS
Click here to download the full size of the above Circuit.

managers do NOT want you messing with critical infrastructure (for good reason), and I personally don`t want to get on the bad side of anyone who gets stuck in an elevator because of me. (Around here the winner has been known to choose the loser`s tattoo. ) However, it occurred to me that it might be possible to make a completely self-contained unit, discreetly placed above the elevator`s drop-ceiling, that could detect when the elevator starts moving all by itself. How By using an accelerometer. An accelerometer measures, logically enough, acceleration. This is different from velocity - while a car (or an elevator) is accelerating from stopped to cruising speed, the accelerometer will read > 0. But once the car (or elevator) has reached cruising speed and the velocity is constant, the accelerometer will read 0. When you decelerate, the opposite happens - the accelerometer will read < 0, until the car (or elevator) has stopped, at which point the accelerometer will again read 0. To see what kind of numbers we were dealing with, I hooked up an Arduino, an ADXL345 and an Openlog. (Tip: the Openlog is a great tool for early development work like this - it stores all the data you can generate, making it easy to analyze later and see what you can do with it). I took a quick trip up and down in the elevator, popped out the SD card, loaded the data into a spreadsheet, and made a quick graph: In the above graph, the approximate...

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