Do-not-disturb adapter for telephone receivers

Claim 1

In a telephone system having a ring control line for conducting ringing signals to a telephone receiver, apparatus comprising: a switch connected to the ring control line, said switch including a first and second contacts, said switch moveable between said contact position and connecting the ring control line to the ringer of said telephone receiver in said first contact position; a resistor substantially equal to the telephone receiver ringer impedance connected between said second contact and ground, said resistor coupling the ringing signals to ground whenever said switch is placed in said second contact position; a plurality of cams having substantially circular peripheral edges, each of said peripheral edges having at least one indentation therein; means for rotating said cams at a predetermined rate for a selectable time interval comprising a mechanical timer, said timer including a rotatable shaft coupled to said timer, said cams being mounted on said rotatable shaft; and means for moving said rotatable shaft longitudinally to selectively engage one of said cams along said peripheral edge with said switch; said cam opening and closing said switch between said first and second contact positions as said peripheral edge of said selected cam moves past said switch.