Help with specialty alarm circuit

Discussion in 'The Projects Forum' started by oceanrowsolo, Aug 20, 2009.

  1. oceanrowsolo

    Thread Starter New Member

    Aug 20, 2009
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    Hi, I'm using a special device, a radar target enhancer, and need a circuit design that will do the following:

    1. Runs on 12vDC, when a signal is detected from a radar source, the circuit should:
    A. Trigger a LED lamp
    B. Trigger an audible alarm that can be switched off

    When a radar signal is detected, a line with 5vDC goes to 0 vDC, this is the trigger/alarm line provided by the radar target enhancer already in place.
    Since the unit will be 'hit' by radar every second or seconds, it would be good to have a timer circuit, perhaps adjustable, that would 'ignore' the multiple hits for X period of time (something like 1 minute).

    This is a marine application for use on a transoceanic row boat. Any help or suggestions is greatly appreciated. I can solder and follow a circuit design, but don't have the skills to create the design. Please help if you can....

    Thanks kindly!!

    W. Vidmar
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    A "target enhancer" sounds is if it should be something to give a larger return to the radar, like a corner reflector, also called a Mongolian ghost trap.

    You seem to be interested in a radar detector that indicates when you are receiving radar energy. Radars use a wide range of frequencies. Would you happen to know the frequency and repetition rate of the radar you wish to detect?
     
  3. jj_alukkas

    Distinguished Member

    Jan 8, 2009
    751
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    You need a low logic trigger.

    In the following circuit, replace the relay with a 12V low power buzzer with switch along with an LED indicator in parallel. If your buzzer or siren is a heavy one, connect it after the relay.

    [​IMG]
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    jj,

    With 5v logic input and a +12V supply the PNP transistor and relay will be ON whether the input is +5v or 0v. If there is a 5v supply for the logic, maybe he could use a 5V relay. That could switch the 12V LED and buzzer.

    Ken
     
  5. jj_alukkas

    Distinguished Member

    Jan 8, 2009
    751
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    Oh ya, thats right. Forgot it. Thanks for pointing it out.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Cascade two NPN transistors, two resistors, and the relay from the +12V to the second collector would allow logic level switching of the 12V relay.

    ken
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Just throwing this out as a straw man- to throw darts at: Assuming +5V is not available, using optical-coupler with +5V on signal line there should be no current flow thru emitter; when sig. is lo , 20mA will flow, grounding R2, triggering C555. Select R3-C for desired blockout time[ 3MΩ, 47μF etc ]. C555 has poor hi capability, so a FET is used to drive load.R5 to fit LED's used. "S" is sonalert or other sounding device. Have a good-safe trip.
     
  8. oceanrowsolo

    Thread Starter New Member

    Aug 20, 2009
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    0
    Hi,

    Thank you for your suggestions and schematics.

    The device I'm using, an active radar target enhancer, already exists and has three wires coming from it; +12VDC, Ground, and a +5VDC signal that goes to 0 VDC when hit by marine ship radar.

    With the above in mind, which of the proposed solutions would be best?

    Beenthere; the device already works (commerically made) and is in use on ships and unmanned buoys around the globe - hence no need to worry about freqs and such. And yes, the device gives out a signal to make me look at though I'm a 150' blob on the other ships radar, rather than the 24' row boat I will be on....

    Thanks kindly,

    W. Vidmar
     
  9. jj_alukkas

    Distinguished Member

    Jan 8, 2009
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    Thats the solution with minimum components.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    JJ's two npn's ,good idea with relay or inhibit timer using 555 IC as one-shot. Blockout time about 1 sec per micro farad.
     
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Sorry Ken mis read post.
     
  12. jj_alukkas

    Distinguished Member

    Jan 8, 2009
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    5
    I think 2 transistors make it even easier ..
     
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