Relay for siren on police car

I am installing a video camera (Watchguard) in a police car and I am needing a 12 volt (+) input off the siren speaker for a siren sensor. The speaker output wires show a 35 volt AC current. Any ideas how to apply a relay to the 35 volts AC so I can get a 12 volt (+) feed to one of the sensors in the camera. I am trying not to have to go inside the siren controler itself to get a 12 volt (+) feed when the siren is activated.

Thanks for any help.

Bobby

leeso20@wmconnect.com

R1 and R2 drop the input voltage since the regulators max is 35.

D1 stops the sirens negative phase from bleeding C1

C1 keeps the regulator alive during the negative phase. You made need to adjust it up to maintain a flat output.

U1 is a standard 12 volt linear regulator

Thanks for the diagram. I am getting the stuff together now.

B. Bean

All of them do turn on with the lights.

The siren feed is most often used to put an icon on screen to indicate that the siren was active. Its a liability thing in case the cop t-bones someone going through intersection and the other driver claims did not here him coming. Or when a driver claims he didnt pull over becouse he didnt here the cop.

The siren feature is rarely hooked up for the reason you stated and because its a major pain. Out of 8000 vehicles I've only done about 10 with siren.

Most video camera systems have a siren interface option board. It taps in to the siren speaker wire with a small transistor and sends a signal back to a sensing wire in the camera system harness. This usually records a "S" on the display to show the siren was sounding at that time.

John Liguori