laser security device for bedroom door

Discussion in 'The Projects Forum' started by betsingerb, Jan 21, 2014.

  1. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    Hi all. 1st post here. I have just a little knowledge of basic electronic theory and wanted to get some help designing something quite simple.

    Basically a good way to detect if someone passed a motion detector, preferably, or broke a laser at the entrance of my room at least once.

    After at least one of these events it would just illuminate an LED until I turned it off.

    Most of the time people have used a laser on youtube (and a buzzer instead of light), but as you can image, not having to setup a laser would be a lot better.

    It's for a dark indoor environment.

    Can anybody help my with a circuit for this? Thanks
     
  2. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    hmm, picked up an PIR infrared sensor from radio shack. Got it working just need to figure out some way to have each IR event add 1 count to a seven-segment display.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Please post a link to the PIR sensor you purchased.

    Ken
     
  4. tshuck

    Well-Known Member

    Oct 18, 2012
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    A microcontroller would make this pretty easy, but without knowing the level of your electronics knowledge, it's hard to make a recommendation...
     
  5. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    http://www.radioshack.com/product/index.jsp?productId=28386046

    it takes 5v or 3.3v. then has a ground pin and an "out pin"

    I actually did also buy an arduino uno R3 at the same time. Very little coding experience but i could check out codecademy.com or something.

    I got the IR working with the arduino with simple "if" statements to forward voltage to an LED if there is an IR event. I copied it from a youtube video someone made. It worked.

    I understand that I could just use a 9v and not use the arduino here.

    I have seven segment displays, about 100 caps, and 1000 various resistors, op amps, transistors, breadboard etc. I have some knowledge of Ohm's law and things.
     
    Last edited: Jan 24, 2014
  6. tshuck

    Well-Known Member

    Oct 18, 2012
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    Sounds like you have a direction to go in already.;)
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    An easier solution would connect the output of that PIR to an N-channel logic-level MOSFET. Get a digital counter, like a golf tally counter (dirt cheap on eBay). Open the counter and solder the MOSFET's source (and PIR's common) and drain across the pushbutton switch's contacts...watch polarity. Done!
    I've done this before with multiple stopwatches and a CD4066 quad analog switch.

    Ken
     
  8. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    ill try that out actually. Thanks for your help guys
     
  9. #12

    Expert

    Nov 30, 2010
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    Quote: a microcontroller would make this pretty easy"

    How can you possibly say this?
    Do you mean a microcontroller would make this pretty easy right after you know how to program one, have the equipment to load the program into it, and know how to design and assemble the required circuits to support the microcontroller...or is it easier than that?
     
  10. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    dunno he said he doesn't know my level of knowledge. But the golf counter thing sounds perfect.

    EDIT: ok nvm haha didn't read everything

    I took about a year of EET at a tech school here in La Crosse and am just fascinated by electronics.
    A nice win 8.classicshell computer i built so i have the computer to program a microcontroller on (or copy someone else's code onto)
     
    Last edited: Jan 24, 2014
  11. #12

    Expert

    Nov 30, 2010
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    You fooled me. That's more than, "just a little knowledge of basic theory".
     
  12. inwo

    Well-Known Member

    Nov 7, 2013
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    I have the same education.:) Taking a class there in 1964.:eek:

    I'm just across the river if you ever need a part.

    "Hokah Forever"
     
  13. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    I did the mosfet thing but with a pedometer. It works great.
     
  14. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    doh just fried the lcd somehow. Only half of the display can be read now. I had a 12V wall adapter into a voltage divider to get the 1.5V required for the meter but apparently 1.6V was too much. Dunno. Ah well
     
  15. #12

    Expert

    Nov 30, 2010
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    A string of resistors used as a voltage divider is only as stable as the current used by the load.

    How accurate do you need the 1.5V and how much current (max) does the load need?

    Here are 5 ways to do it, and this is only a start.
     
    Last edited: Feb 1, 2014
  16. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    It's was a little 1.5v pedometer. I presume the current was very low (mA?) If I were to do it again I'd try to hit 1.5v on the dot.

    BTW I had to look up what to connect the gate to and how a MOSFET works before I made that working circuit. Just to give you an idea.
     
  17. #12

    Expert

    Nov 30, 2010
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    I suppose that means the need is no longer?
     
  18. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    actually i just bid on one on ebay for $1.75. So I'll try it again in a week or so.
     
  19. betsingerb

    Thread Starter New Member

    Jan 21, 2014
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    I'll see what this pedometer uses for power.

    I know this PIR sensor says 3.3V - 600MicroAmps; or 5V - 800MicroAmps

    EDIT: I got the pedometer to work. the screen was falling off, I put the housing back on and that holds the pedometer screen to the pedometer PCB
    It was some weird rubber strip interface that just gets smashed against the PCB when in its housing.

    Just got a 1.488 V output out of a resister voltage divider and everything seems to work. Thanks
     
    Last edited: Feb 1, 2014
  20. tshuck

    Well-Known Member

    Oct 18, 2012
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    Looks like I lost this thread a few days ago...

    I was testing the waters as the OP said he/she had no experience, yet knew all the right words to say and even brought in a new technology. With this in mind, I was going to suggest something like the Arduino/PICAXE for the OP to mess around with - something that typically comes bundled with any required hardware.

    While yes, there is a rather simple design to complete the task without a microcontroller, I figured that the OP, considering a more advanced knowledge than most, would want to learn more about electronics and make more advanced projects as time went on.

    With the OP changing his/her mind so quickly on a proposed solution, a configurable device would accommodate many changes in design without changing much hardware.
     
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