Help with specialty alarm circuit

Thread Starter

oceanrowsolo

Joined Aug 20, 2009
2
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
 

beenthere

Joined Apr 20, 2004
15,808
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?
 

jj_alukkas

Joined Jan 8, 2009
753
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.

 

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KMoffett

Joined Dec 19, 2007
2,765
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
 

KMoffett

Joined Dec 19, 2007
2,765
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
 

Bernard

Joined Aug 7, 2008
5,227
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.
 

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Thread Starter

oceanrowsolo

Joined Aug 20, 2009
2
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
 

jj_alukkas

Joined Jan 8, 2009
753
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.
Thats the solution with minimum components.
 

Bernard

Joined Aug 7, 2008
5,227
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.
 

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