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A Tiny Wireless Motion SensorAll > Tech > Inventions > A Tiny Wireless Motion Sensor by natetrue
Prologue You pause just before turning the corner into the dark hallway. You've evaded the guards thus far, but your adventure is not yet half over. Hearing a noise, you duck into the nearest doorway, disappearing into the shadows. A guard passes by. Damn, why do they always have to hire guards with muscles? It's, like, intimidating. Nevermind that now. After a tentative glance you move back into the hallway. At the end a glass door with the words "Secret File Room" etched into it stands, beckoning to you. You glide down the hallway silently to the door. You switch on your wireless motion sensor and stick it on the wall next to the door, then advance inside the room. The receiver makes a soft click as you slide its switch to the 'on' position. A gentle hiss lets you know it's receiving properly. You'll know if anyone is coming. Suddenly, you hear the familiar ringing sound come from the receiver. You timed it just right - the hot female secretary just walked in. Looks like this mission just got a little more interesting. The Concept This time, I wanted to create a gadget for the super-spy in all of us. I'll say right up front - I know this device isn't useful in the everyday, law-abiding lifestyle we all practice during the day. But I made it anyway. The idea was to put together a movie spy-gadget grade device both on the cheap and very small. Usually the gadgets you see in movies are fictionally created by well-funded government agencies with top scientists. It's not all Hollywood magic - you too can create fun spy gadgets without needing to break the bank! Wow, that sounded really cheesy. On with it, then. 
Motion sensors (or, to be more specific, "passive infrared motion sensors" or "PIR motion sensors") sense motion based on changing levels of infrared heat in their field of view. 
contains two pyroelectric sensors. When there is a difference in heat between the two sensors, the alarm is raised. The big white lens serves to divide the outside world into alternating bands lighting each half of the sensor in turn. Thus, when someone crosses between the bands, the motion sensor trips. Initially, I saw this specific motion sensor module at MPJA.com, but they're out of stock now. Theoretically, any motion sensor can be used for this purpose. All it needs to do is send a temporary logic high level somewhere on its circuit board when the alarm trips. Most motion sensors should have that. What piqued my imagination with this motion sensor was the size. It's very small and quite suitable for covert-style use. I wondered, what could I do with it? 
Ah, my old friend, the TX433. As seen on my wireless color-changing abstract decoration writeup, the TX433 transmits any signal over the 433MHz unlicensed radio band to the receiver. It's currently available at the Canadian QKits, or you can find similar modules on eBay (look for 433 transmitter). These things are wicked awesome - they pack a whole lot of usefulness into a tiny, tiny package. 
at QKits or ebay://433 receiver) with batteries and a small piezoelectric speaker. When it receives the transmission from the transmitter, the sound plays on the speaker. I opted for this approach over having a hardware detector because it's far easier to hear a signal than it is to genuinely decode it. Notice the ghetto power switch on the wrought-wire battery holder. Now that's professional. Conclusions I'll admit again that it's not the most useful thing in the world, but whether you're committing international espionage, corporate espionage, private investigation, jewelry heisting, or just good old-fashioned dumpster diving, this device finds its niche in many not-so-common situations. Comments:  |
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