Help: external siren/output from radar detector?

[mnapuran]

Wasn't sure exactly how to phrase the title.. but here's the possible scenario's.

1) Looking for a circuit that can go inline w/ the power connector of a radar detector, detect a voltage draw from the detector (indicating it is going off) and then trigger an external siren or even just provide a relay output.

2) Looking for a circuit that can plug in to a 3.5mm audio headphone jack, and provide output as above (see #1)

I would think #1 would be easiest.... anyone?

-Mike

 

[Hero999]

You really need to provide more information.

What type of output does your radar protector provide and at how much current?

The chances are, all you need is a transistor and a relay.

 

[mnapuran]

Well, going route #1, I'd like this to circuit to be pretty generic. In other words, be able to work with various radar detectors. Obviously, each will have it's own idle current (quite low) but when lights/alarm on the unit goes off, the draw will certainly change. Of course, the detectors work on roughly 10 to 15 volts DC. On the output side of the circuit, it really only needs to be a latching relay or something similar to drive an external 12v siren, light, or whatever.

 

[Hero999]

Have you already got the detector?

I was assuming that you just needed a switch that will connect on to the output of it.

 

[Super_voip]

I've seen these circuits before , maybe in "Radio-Electronics" back in the early 80's. Place a resistor(small value) in the power lead and use a comparator to detect the voltage change across the resistor.

 

[Hero999]

That's a good idea.

He might even be able to use a current transformer, the pulsed current generated from the siren might be enough to create an AC signal in the secondrary.