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making cheap security circuit

Discussion in 'Misc Electronics' started by Mack, Aug 7, 2006.

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  1. Mack

    Mack Guest


    I am an electrical engineering student at the University of Cape Town,
    South Africa. I just wanted to know how to connect a circuit using 555
    timer, beeper etc to the plugs in the wall. I thought of the
    transfromer of course, but I'm having trouble with drawing the circuit
    for it. I intend on using a laser with a LDR in a voltage divider to
    detect motion. Is it possible for someone to maybe sketch something
    that i can work on?
  2. default

    default Guest

    Try google. What you ask for is already out there. The problem is
    sifting through all the chaff to find it.

    Look at
    simple circuit to detect a laser or other light source to use in a
    "break beam" detector circuit. Scroll down to "Laser Surveillance."

    Likewise . . . you mention 555 you want the thing to alarm for a
    predetermined time? Those circuits are on the web and in the "data
    sheet" information for the 555.

    Transformer - use a wall wart power supply

    Tons of circuit sites to comb through with similar information on
    them. has a few links on it

    robot builders and model train buffs use similar circuits

    Plenty of IR detector circuits out there too - substitute a visible
    light detector element or just incorporate some of the circuit into
    your design

    I've designed several ir circuits that use a modulated light beam -
    harder to foil by just swamping the detector with white light - it
    only detects light that is modulated with the right frequency. I
    haven't used lasers for the light source but all it should take is
    substituting the laser for the visible LED (and reduce the power
    supply voltage to something the laser could live with - I pulse the
    diodes from a +22 volt source with peak of a half amp and average
    power of only 60 milliwatts)

    I can email a jpg of the circuit - three integrated circuits and more
    complicated than the basic circuit on sam's repair web site. Just the
    transmitter and receiver and frequency modulation circuit - no timer
    or other stuff an alarm would require.
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