Circuit for controlling the duration of an interval between sound signals

Claim 1

A fog horn for automatically emitting successive sound signals and in which the duration and interval of such signals may be manually preselected in accordance with prevailing weather conditions and navigation rules comprising: a. a sound emitting device; b. a source of direct current electric power; c. a timing capacitor; d. a double-pole, single-throw relay; e. a trigger circuit connected in series between said source of direct current and said timing capacitor to provide a conductive path when said capacitor is charged to a preselected value; f. a switchiNg transistor connected between said trigger circuit and said relay to connect a first set of contacts of said relay with said source of direct current when said trigger circuit and switching transistor are made conductive, said first set of contacts of said relay providing connection between said source and said sound emitting device when made, said switching transistor connecting a second set of contacts of said relay with said source of direct current when said trigger circuit is non-conductive; g. a variable resistance connected in series between said relay and said timing capacitor for discharging said capacitor when said first set of contacts of said relay is made so as to control the ''''on'''' of connection between said direct current source and sound emitting device; and h. a second variable resistance connected in series between relay and said timing capacitor for charging said capacitor when said second set of contacts of said relay are made, said second set of contacts of said relay providing no conductive path between said sound emitting device and said direct current source to provide an ''''off'''' period of connection between said sound emitting device and source, said ''''off'''' period being controlled by said variable resistance and said timing capacitor, whereby the duration of said ''''on'''' and ''''off'''' period may be varied.