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Stealth-Action Motion Sensor System

Have you ever watched a spy film, or played a stealth-action video game (like Metal Gear Solid) where the hero deftly bypasses the high-tech alarm system? Well, this system is just like that – gives the intruder a sporting chance. (And it’s even shootable if you add some parts.)



Have you ever watched a spy film, or played a stealth-action video game (like Metal Gear Solid) where the hero deftly bypasses the high-tech alarm system? Or watched a Cat Burgler/diamond heist movie or show (like Impossible Heists) and thought that navigating the obstacle-course security systems looked kind of fun? That’s because those “movie-style” security systems are pretty fun, and this project is how to make a movie-style motion sensor with floodlamp and audible alarm. It’s specifically designed so that you can easily make modifications.

It’s the motion-sensor equivalent of saying “Before I kill you, Mister Bond…”

WHAT THIS IS

This is a motion sensor alarm, meant to be used as part of a “Hollywood movie-style” security system. It’s made from a portable lamp, a personal alarm, a PIR (passive infrared) motion sensor, and a microcontroller to tie it all together. It can easily be modified and can even be made “shootable”. That last part is a plus because while in the real world a sensor’s destruction might cause an alert, but in a movie-style security system a sensor being destroyed is just plain ignored!

What do I mean by “Movie-style”? Well, in Movie-land security systems are more like an obstacle course than a barrier. There are copious blind spots to coverage, and sensors can be fooled or bypassed with simple tricks. Air ducts are big enough to crawl through. Guards shrug and say “I must be imagining things!” before turning their backs. It’s great fun.

In the REAL world, the laser tripwire grid would not have gaps big enough for a human to slip through. Motion sensors will not indicate to an intruder how close they are to triggering. Shooting the keypad doesn’t open the door, and shooting a camera or other sensor to destroy it will probably cause an alert because sensors aren’t supposed to suddenly go offline… But what fun is all that? None! That’s what Movie-Style Security Systems are for, and this is how to make a motion sensor for part of your own movie-style security system.

HOLLYWOOD SECURITY SYSTEM

REAL WORLD SECURITY SYSTEM

USES OF THE MOVIE-STYLE MOTION ALARM

  • Making your own movie-style (or videogame-style) Assassin/Spy/Diamond-Thief training course.
  • Making your own reality-show style game, like in the TV show Impossible Heists.
  • Terrifying your drunken housemate as they come in at 4am.
  • Making your own Airsoft or Laser Tag based obstacle/challenge course.
  • Or even as props for making your own movie.


PREREQUISITES

This project uses some electronics and a PIC (12F629). If you own or have access to a PIC programmer (and know how to use it!) you will be able to make and modify this project as long as you possess basic electronic skills. If things and terms like regulated voltage, HEX files, relays, and pullup resistor don’t mean anything to you then you will have problems if you try to make this project.

WHAT THE MOVIE-STYLE MOTION SENSOR DOES

The movie-style motion sensor has a slow-blinking heartbeat LED to indicate an active state in “scan” mode. When motion is first sensed, the LED lights a solid red and enters an “attention” mode for 10 seconds. If further motion is sensed while the sensor is in “attention” mode, the ALARM is tripped. If 10 seconds pass and no further motion is sensed, the sensor returns to “scan” mode and the LED resumes a slow blink. (The ALARM consists of an audio alarm and a floodlamp, but you can easily add or substitute your own devices to be triggered.)

A “Reset” button exists to cancel the ALARM. A “Disable” input also exists to shut down the sensor until it is reset.

HOW TO BYPASS THE MOVIE-STYLE MOTION SENSOR

As a result of the design, the motion sensor can be bypassed by carefully and slowly walking past it and closely observing the LED indicator. When the LED indicator lights solid (the sensor enters “attention” mode), the intruder must FREEZE until the sensor goes back to “scan” mode. If the sensor detects movement while in “attention” mode, the alarm will be triggered!

If the ALARM is sounded, the RESET switch can be hit to return the sensor to a “scanning” state.

Alternately, the intruder may disable the sensor (and alarm, if triggered) at any time by hitting the DISABLE switch. The sensor is returned to normal operation after a DISABLE by hitting the RESET.

By the way: PIR (Passive Infrared) motion sensors, such as the one used in this project, are most sensitive to movement ACROSS their field of vision, but less sensitive to movement directly towards or away from them.

HOW TO BUILD THE MOVIE-STYLE MOTION SENSOR

The Movie Motion Sensor is battery-powered and designed around a portable and rechargeable floodlight (which is really just a battery, a switch, and a bulb), a motion sensor unit ordered from a supplier, a personal alarm from the 1$ store, a PIC, and a few other bits and pieces. Since I managed to get the lamp on sale for 10$, the total cost of all the parts wasn’t much more than 30$.

The core of the sensor is the PIR Motion Sensor and the 12F629 PIC. The PIR unit provides the raw motion sensing and the PIC processes the output from the PIR and decides what to blink or turn on when. This design does two things when the ALARM is triggered. It turns on the floodlamp (via a relay), and turns on the loud personal alarm. The outputs can easily be used to trigger other devices of your choice instead of (or in addition to) the lamp and audio alarm.

OPERATION DETAILS

Here are some details regarding the operation of the sensor:

1. When first powered up, the LED does a fast blink for 2 minutes to let the PIR unit calibrate and settle. During this time, the unit cannot be triggered.
2. When the ALARM is triggered, the ALARM state lasts for 5 seconds (or until Disable or Reset is hit).
3. When the Disable button is pushed, the entire device is shut down until RESET is hit.
4. When the Reset button is pushed, the device goes back to “scanning” mode.

SCHEMATIC

Click for larger version

Files:
HEX file ready to be programmed into a PIC: 12f629-PIR-Alarm.hex
PICBASIC Code: 12f629-PIR-Alarm.bas

Parts:
1. The audio alarm is a simple “110dB personal alarm” from the 1$ store; any audio alarm that is powered by approximately 5-6V should work.
2. The PIR unit is item #35050 from HVW Technologies which ships to Canada and USA.

ONE STEP FURTHER – HOW TO MAKE IT SHOOTABLE

If you own an Airsoft gun, you can make the sensor “shootable” by connecting a piezo element and a small sensor circuit to a small piece of plexiglass/lexan/polycarbonate and feeding the output into the “/Disable” input of the PIC. The Movie-Style Motion Sensor will be disabled if the sheet of polycarbonate is shot. The sharp impact from the BB hit will transfer into the piezo element (superglued to the sheet of polycarbonate) which will trigger the DISABLE input of the motion sensor circuit.

(This was only made with Airsoft guns in mind. If you own a Laser Tag gun, you’ll need to roll your own sensor for detecting a “shot”. If you’re using a paintball gun, you’re probably better off actually shooting a switch with a target on it to trigger the Disable input, since paintballs carry a lot of Oomph to them and can easily trigger a beefy switch. Also paintball hits are messy, so keep that in mind. Finally, if you’re using a real gun… well, I think any way you slice it the disabling of the device will be permanent in that case.)

This modification assumes you have the electronics knowledge to follow the schematic below. The circuit shown will pull the /Disable pin on the PIC low when the piezo element detects a sharp and strong impact on the polycarbonate plate it is bonded to.

This is not a foolproof system, but it seems to work fine on my workbench with a spring-powered USP and it uses very few parts. Your mileage will probably vary.

Remember that the polycarbonate sheet is what has to be hit for the shot to be detected! Don’t shoot the PIR element or other parts of your sensor unit – even with Airsoft BBs – unless you want them possibly damaged or disabled for real!

Note: The PIR sensor will not work properly through a sheet of polycarbonate – so since you can’t put the PIR behind the polycarbonate, you might want to put it somewhere it isn’t likely to get hit. At 10-15$ each they’re not exactly cheap.

Click for larger versions

VIDEO DEMO

This is a brief video demonstrating the basic operation of the completed prototype.

It demos the triggering of the alarm as well as the disabling of the alarm by shooting the added lexan plate with an Airsoft spring gun.