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A Tiny Wireless Motion Sensor

All > Tech > Inventions > A Tiny Wireless Motion Sensor by natetrue
NEW! - see me present the Wireless Motion Sensor in action on Gear Live's Bleeding Edge episode 006!

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.

The Motion Sensor

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.
This is accomplished through the virtue of a pyroelectric sensor, seen here as the metal can at the right. Pyroelectric sensors convert infrared heat energy into electrical currents which can be processed. In motion sensors, each metal can
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?
The Wireless Transmitter

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.
In my implementation, since the motion sensor only puts out a logic high pulse, I needed to use an IC to generate a sound when the motion is detected. This was accomplished with the HT12E Remote Control Encoder IC, but you can use a simple oscillator or sound effect IC or whatever you want. The idea is to make something audible so the receiver can pick it up. Hookup is easy - the HT12E just needs power and a resistor for its oscillator. The pulse from the motion sensor powers the HT12E encoder and the transmitter. This way the transmitter and encoder aren't powered when they don't need to be, saving mondo battery life.
Here's the transmitter prototype on a breadboard. You can see the motion sensor dangling off toward the back and the HT12E in the board. The TX433 is off to the right.
Here's the assembled transmitter. As you can see, it is very small.
Here's a back view. You can see the transmitter mounted to the rear of the motion sensor, and a small board attached to the bottom with the HT12E on it.
The receiver couldn't be simpler. It's the lovable old RX433 (again, available
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.

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Comments:

Posted by devcayer 7 years ago ( 02-Dec-2006 13:22:29 )

Hey natetrue,

Dude the stuff you make is very awesome, i'm very impressed. A lot of your stuff deals with electronics. I've taken a few programming classes, but I'm not sure how to apply like what you do. Is there any way you could direct me to books you or sites you may have learned at that teaches how to connect circuit building/software, ? Thanks a lot man, and keep up the good work

Devcayer

Posted by squashman 7 years ago ( 08-Jan-2007 15:00:48 )

can someone out there help me I want to put into a bird nest box a cctv camera and want to include a motion sensor to swich on the camera when the bird comes into the nes box I have the cameras my email adress is pajanes@hotmail.com
peter
Attached image:

Posted by konceptskool 7 years ago ( 01-Feb-2007 01:22:01 )

Hey natetrue this is really something...I would like to talk to you about this...

Posted by cincyghosthunter 7 years ago ( 26-Apr-2007 12:30:21 )

What type of range does this have, it might be usefull in my ghost hunting/investigations

Posted by natetrue 7 years ago ( 26-Apr-2007 12:53:26 )

It should reach for about 500 feet, but that depends on building and/or terrain.

Bust any ghosts yet?

Posted by joeinvegas 7 years ago ( 18-Jul-2007 16:12:32 )

Can this be used to close or open a window on my computer if I don't want someone to see what I am doing online. (internet poker perhaps) I think it would be a cool application of this device.

Posted by trixter 7 years ago ( 23-Jul-2007 13:06:00 )

Hi, I like the gadget and may have a use for it. Would like to know if this motion sensor could trigger a stand alone light and a audio pitched reciever?

\cheers mate

trixter

Posted by deffboi 7 years ago ( 10-Aug-2007 12:25:17 )

hey nate,

this thing rocks! i really could do with one of these... but i'd opt for a vibrating alert... because ppl hearing it all the time might get sussed, and also cuz i'm hearing impaired and might not be able to pick up the frequency:P... other than that, awsome! i can see lots of uses for this lil gadget.

-deffboi

Posted by rickyboy 6 years ago ( 07-Dec-2007 02:53:17 )

hi, i think this stuff fits to my needs which i urgently need. I found something like this but it's to expensive. how can i be able to have this gadget for my use? I tend to use this gadget in my pickup type vehicle. hoping for your response and email me asap. Nice stuff.

Posted by bitsangou 6 years ago ( 10-Jun-2008 12:53:42 ), comment hidden (show)

this is a very good invention. I think that this could keep the ladies in my life safe like when they are in the laundry room by them selfs, so no one can sneak up on them. It will also be fun to play around with. I saw a few of the other comments and thought that it would be cool if the receiver had 4 different settings: 1)flashing light mode 2) audio mode 3) and a vibration mode, and it would also be cool to have a combo between them. I don't have any skills in this field yet and was wondering if you had any suggestions on how to put something like that together, or if you had any existing kits for the motion sensors for sell. It would be cool to hear your input, and once again (if you haven't heard it from everyone else a thousand times already), Great invention.

This comment was edited at 2008-06-10 13:02:57


Posted by bitsangou 6 years ago ( 10-Jun-2008 12:58:37 ), comment hidden (show)

this is a very good invention. I think that this could keep the ladies in my life safe like when they are in the laundry room by them selfs, so no one can sneak up on them. It will also be fun to play around with. I saw a few of the other comments and thought that it would be cool if the receiver had 4 different settings: 1)flashing light mode 2) audio mode 3) and a vibration mode, and it would also be cool to have a combo between them. I don't have any skills in this field yet and was wondering if you had any suggestions on how to put something like that together, or if you had any exiting kits for the motion sensors for sell. It would be cool to hear your input, and once again (if you haven't heard it from everyone else a thousand times already), Great invention.

Posted by esegre 6 years ago ( 25-Jul-2008 20:38:09 )

hi Nate:

I build these kind of gadgets for a living ,and the main problem
with your sensor or any sensor for that case is that if installed
in a place where many people pass during the day for example
for every pass the battery will drain and after one day you will
have no battery.
In proffesional IR sensors we use a microprocessor to turn off the
transmitter for 30 seconds after each trigger ,that way you dont
lose reliability but the battery drain is drastically reduced
Enrique Segre

Posted by rahulsingh 6 years ago ( 25-Sep-2008 12:39:30 )

Hii...i liked this creation....
i am thinking of designing a motion sensor that can detect the head movement to control the pointer of the computer whih is othrwise controlled by d mouse....cn dis sensor prove to b of any use...????
plz reply...ma id---raul.singh87@gmail.com

Posted by johnsegg 5 years ago ( 26-Jan-2009 03:15:52 )

thats very cool

This comment was edited at 2009-01-28 10:59:02


Posted by stubie 5 years ago ( 14-Jul-2009 09:32:28 )

Hi natetrue

I love the gadget! I'd really like to try something like this out with intruders. Anyway I could convince you to tell me more?? Please contact me at aus_executer@hotmail.com

Cheers
Stubie

Posted by denisdjdss 4 years ago ( 18-Feb-2010 11:53:01 )

I was looking for sites on pirs and found yours. Im not familiar with this much but thought you may help. I want to put a pir on a usb and plug it in to my computer. Why? Well I dont know for sure but thought it would be nice to see what it reads. Does this make since?? I want to make a sensor that triggers a response and a program that reacts to it. (using usb cable or blue tooth). Thanks My email denisdjdss@gmail.com

Posted by bymadak 3 years ago ( 30-Jul-2011 03:11:42 )

Hi natetrue

I love the gadget! I'd really like to try something like this out with intruders. Anyway I could convince you to tell me more?? Please contact me at kamilsense@gmail.com

Cheers
www.b-8.net

This comment was edited at 2011-07-30 03:12:10


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