PIR's and infared emitters

Discussion in 'General Electronics Chat' started by mbohuntr, Aug 16, 2010.

  1. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Well, here is a question for the PIR experts. One of the suggestions for my mailbox surveilence project involved a heated resistor. I'd like to place a piece of tape over the fresnel lense, and place an infared emitter under the tape on one side of lense. My question is; If I understand the PIR operation correctly, it acts something like a comparator. If either of the sensors goes high, the output goes high.
    If I place an IR emitter in the 940 nm range, and 13-15mW output, will this damage the PIR by hypersaturating the sensitive sensor? Thanks all.
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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  3. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Try this quick experiment first, cover half you lens and light a bic lighter in front of the exposed side. Chances are it won't fire.

    The Freznel lens is actually made up of many finely divided lenses over it's viewing angle. Covering half the lens will only reduce the viewing angle. It would be impossible to cover up the lens to omit one of the sensors. The action of the freznel is to have the infrared source cross the two sensors, oppositely biased, to create a trigger pulse. If you take a magnifying glass you can see how finely divided the lenses are.
     
  4. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Hmm, thanks you guys, perhaps i'll try to trigger it without the tape in a controlled enviroment. The tutorial mentioned it could be triggered by a bright light suddenly flashing.
     
  5. BMorse

    Senior Member

    Sep 26, 2009
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    PIR's are sensitive to a change in temperature, so if the "light" source was a source for "Heat" then it may work, But in my personal experience with PIR's, I do not believe you can trigger them with just an IR emitter......

    Why not wire a switch to the mailbox? When the door is opened it could close the switch to have the camera take a picture (You could even wire the switch directly to the shutter switch)? Although you may get a picture of your postman, but it is much simpler than trying to mount a sensor to do so, with the switch, it will not be bothered by passing cars or any other moving object, only time it will trigger is if the mailbox opens.....

    And another thing too, most digital cameras have a power down time out, so if the camera was not being used for a few minutes, it will power down, How are you going to address this issue?

    B. Morse
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Good point, even when run off an aux supply my camera times out.

    I'm all for the (see other thread) fake camera with the very bright flashing LED aimed at the box.

    Alternately a simple "latching switch" can be made by mouting an insulated spring contact then keeping it from touching the box with a piece of plastiic. Tie a piece of string from the plastic to the box door, when it's opened it pulls the plastic and sets off one of those nasty sounding sirens somewhere. Set the logi and horn up away from the box such as up in the tree so he can't go and start pulling wires, chances are he'll just run.

    Again with this idea you've got to temporarily suspend mail delivery.

    Wireless monitor cameras also abound, an old VCR with timed record or your PC can be the recorder.

    And again - complain to the postmaster. One complaint by your neighbor may not be enough to trigger action, two or more may.
     
  7. marshallf3

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    Jul 26, 2010
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  8. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Thanks, I would have to hack into that as well. (just the on/off switch) hmmm... now I just need some free time...
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Hack perhaps but as you mentioned it would be an easy one. Full motion video would likely be preferred in your situation as you'd stand a better chance of getting some full face pix of the entire gang if there's more than one involved.
     
  10. Markd77

    Senior Member

    Sep 7, 2009
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    I've got one of those MD80 spy cams. It's not bad, better quality than my mobile phone. It's got a sound activated mode, but that might get triggered by passing cars. To record normally you have to press the power button, then wait a couple of seconds and press record so that would be a grade 2 hack. Maybe hacking the microphone would be easier.
     
  11. mbohuntr

    Thread Starter Active Member

    Apr 6, 2009
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    Update... the sensor appears to get overloaded with direct flashlight or Infared emitter light, in the test mode, it will freeze up and refuse to trigger. Soooo I managed to partially crack the case, and it has about nine wires. 5 going to the camera from the board, and 4 from board to board. When I get more time, I will power up the cam, and trigger the PIR circuit. I think I might find a 0v pin that goes high when the PIR is triggered. It would be nice to get the unit completely apart to find the PIR output.
     
  12. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    The scouting cam industry is well developed, and you can find some good information online about several of the boards that where popular during the birth of these units. If you camera is a 35mm, chances are there where only several boards being used commercially back then. As well, there is plenty of info as to how many of these early cameras where hacked into to access the shutter.

    It sounds like you are at the point of questioning, do you rip apart a good scout camera unit, or borrow it's concept and apply it to another imaging device.

    The earlier digital cameras are cheap these days, and with some carefull intrusion, can be hacked for remote operation.

    My favourite is hacking the Canon 510/520 where I connect the power switch to the unused USB pin. This then gives full remote capabilities over the USB port. In my devices, the controller is a simple 8051 that accepts a number of triggers.
     
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