Focus control for search lights

A focus control for narrowing and widening the focus angle of a search light beam emitted by a search light on a platform having a DC power source, wherein the search light includes a DC motor, a cam driven to rotate by the DC motor and a focus control operated by the cam for narrowing and widening the focus angle in response to control signals over a single wire interface between a remotely positioned control switch and the motor, the focus control comprising:

• an open position, a power source position and a ground position assumable by the remotely positioned control switch;
• a relay arrangement comprising a first coil adapted to be connected to the power supply and a second coil adapted to be connected to ground with both coils adapted to be connected to the remotely positioned control switch by the single wire interface;
• a first relay switch operated by the first coil and adapted to be connected to a first pole of the DC motor, the first relay switch being selectively connected to ground when the first coil is energized and to the DC voltage source when the first coil is deenergized, and a second relay switch operated by the second coil and adapted to be connected to a second pole of the DC motor, the second relay switch being selectively connected to ground when the second coil is energized and to the DC power source when the second coil is deenergized;
• whereby upon energizing the first and second coils while leaving the remotely positioned control switch open, the cam driven by the DC motor is positively held stationary;
• upon deenergizing the first coil while the second coil is energized, the cam is rotated in a first direction to alter the magnitude of the focus angle in the first direction, and upon deenergizing the second coil while the first coil is energized the cam is rotated a second direction opposite the first direction to alter the magnitude focus angle in a direction opposite the first direction.

A focus control for narrowing and widening the focus angle of a search light beam emitted by a search light mounted on a platform having a power source, wherein the search light includes a D.C. motor, a cam driveable by the motor to rotate and a focus control operated by the cam for narrowing and widening the focus angle in response to control signals over a single wire interface between a remotely positioned control switch and the motor, the focus control comprising:

• an open position, a power source position and a ground position selectively assumable by the remotely positioned control switch, wherein when the remotely positioned control switch is in the power source position, the single wire interface is in a first state different from a second state of the single wire interface which occurs when the remotely positioned control switch is in the ground position, and
• a switching circuit connected between the power source and the motor for reversing polarity of current flowing through the motor, the switching circuit being connected to the remotely positioned control switch by the single wire interface and including an input responsive to a change in state on the single wire interface to reverse the polarity of current flowing through the motor to reverse rotational direction of the motor and the cam to thereby reverse the widening or narrowing of the focus angle, the switching circuit further including a circuit arrangement for connecting both poles of the DC motor to ground when the remotely positioned switch is in the open position and the power source is energized to thereby positively hold the cam driven by the motor is the last position selected upon releasing the remotely positioned switch.