Bulb outage indicator for multi-lamp circuits

Claim 1

A lamp flashing circuit having lamp outage indication comprising a constant voltage source; first relay means including a coil and first and second sets of normally open contacts, the coil being operable when energized to close the first and second normally open contacts; a second relay means including a current sensitive coil and a set of normally closed contacts, the current sensitive coil being operable when energized to open the normally closed contacts; a first series circuit including the constant voltage source, the first set of normally open contacts, the current sensitive coil and a plurality of lamps connected in parallel; a transistor connected in series with the coil and the constant voltage source; a capacitor coupled to the transistor, the capacitor rendering the transistor non-conductive when charged and rendering the transistor conductive when discharged; resistive means connecting the capacitor to the constant voltage source through the first set of normally open contacts when the coil is energized and connecting the capacitor to the plurality of lamps when the coil is deenergized, whereby the capacitor is alternately charged and discharged to render the transistor alternately non-conductive and conductive to alternately supply current from the constant voltage source to flash the plurality of lamps, the current supplied to the plurality of lamps having a greatest magnitude when all the lamps are operable and having a magnitude less than the greatest magnitude when one or more of the lamps have failed, the current sensitive coil being operable to open the set of normally open contacts upon the flow of a predetermined minimum current therethrough, the predetermined minimum current being equal to the current supplied to the plurality of lamps when all the lamps are operable; and a series circuit including the constant voltage source, the second set of normally open contacts, the set of normally closed contacts and indicating means, the indicating means being energized by a flow of current therethrough, whereby the indicating means is periodically energized to indicate a lamp failure when one or more of the plurality of lamps have failed.