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anyone knw photoelectric smoke detector circuit?

Discussion in 'General Electronics Discussion' started by l.rence8, Oct 18, 2010.

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  1. l.rence8

    l.rence8

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    Oct 18, 2010
    i nw do this project..but dun knw hw to start..got any simple circuit of it tat i can use for building and testing it????
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I think you need a new keyboard, and this.
     
  3. ayush

    ayush

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    Oct 31, 2010
  4. davenn

    davenn Moderator

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    Sep 5, 2009
  5. LTX71CM

    LTX71CM

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    May 23, 2010
    Here's a circuit, all known parts and some theory of operation -> lierda.com/product/down_id/755/down.html
     
  6. ayush

    ayush

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    Oct 31, 2010
    @davenn
    The ckt I gave above doesn't use any specialized sensor IC but easy to obtain parts. Since he's asking for a simple circuit I thought he'll be better off with it.

    It's true that a specialised sensor IC like one suggested by LTX71CM works much better, but for project purpose one can always try something simpler.

    @l.rence8
    Whichever you make, do a thorough testing before using it in your building.
     
    Last edited: Oct 31, 2010
  7. davenn

    davenn Moderator

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    Sep 5, 2009

    well what is that COB then ?? its not listed obviously some fancy hard to get part ????
    the designer couldnt even list what it was and many people on that forum were all asking what the COB was and where to get it

    Dave
     
  8. ayush

    ayush

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    Oct 31, 2010
    @davenn
    sry i din mean to offend u

    I forgot to mention about the COB. It's just an ordinary 3 pin melody IC, a UM66 maybe? The circuit maker has left the choice of buzzer to the user. Nothing fancy really.
     
  9. ChosunOne

    ChosunOne

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    Jun 20, 2010
    No! Don't use it in your building.

    Not unless you're using it in addition to a UL-or-equivalent-rated smoke detector. It's okay to put it up as a project experiment, but it's NOT okay to use a first-time homemade project as a life-safety device.
     
  10. LTX71CM

    LTX71CM

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    May 23, 2010
    I second this recommendation. Absolutely don't rely on something you've made for safety, especially when a commercially made and tested iR smoke alarm can be had for $30, the cost of parts for most DIY electronics projects.
     
  11. saradalton

    saradalton

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    Nov 8, 2010
    The home smoke detector circuit warns the user against fire accidents. It relies on the smoke that is produced in the event of a fire and passes between a bulb and a LDR, the amount of light falling on the LDR decreases. This type of circuit is called optical smoke detector. Do not use it as a home smoke detector it’s just for electronic projects.

    This causes the resistance of LDR to increase and the voltage at the base of the transistor is pulled high due to which the supply to the COB (chip-on-board) is completed. The sensitivity of the smoke detector depends on the distance between bulb and LDR as well as setting of preset VR1. Thus by placing the bulb and the LDR at appropriate distances, one may vary preset VR1 to get optimum sensitivity.

    hope this helps.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    In practice that circuit needs either constant adjustment or some form of automatic compensation to allow for aging of the bulb and other long term affects unrelated to smoke.

    Using a LED will improve things somewhat but you still need to consider battery aging and temperature. For instance, you would not want the circuit to get markedly less sensitive as temperature increases!

    But if you're just making it for "fun" then these things are not real issues.
     
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