I am attempting to modify an O gauge whistling tender (K-Line) to work with an existing Lionel Train transformer. The transformer powers the engine with 0-18 VAC. The whistle in the tender is activated by a switch on the transformer that sends out a 2.5VDC carrier wave on the AC line. What I'm attempting to do is activate a relay inside the tender with the 2.5 VDC. The relay then activates the motor for the whistle using the AC power (through a bridge rectifier because the motor is DC). I've been mapping out a schematic and now I'm stuck on how to separate the DC carrier from the AC at the relay coil in the tender. Since this is a preliminary drawing I'll also need to add at least one capacitor and I'm also not sure the 5V regulator is correct either so help on those issues will be appreciated too.