Fuse cap warning light

A warning light device for blown fuse caps having a photosensitive circuit mounted inside an adapter casing that mounts over and is exposed to the fuse element of the fuse caps. The device is powered by batteries contained inside the casing and includes battery energy saving circuits in the form of an intermittent circuit or a low duty cycle circuit that is suitable to provide a visual indication periodically to the user. Light emitting diodes are used as a low power consumption indicating light.

SUMMARY OF THE INVENTION 
It is the main object of the present invention to provide a self-powered 
light indicating warning device that can be easily installed on existing 
conventional round fuse caps. 
It is yet another object of the present invention to provide such a device 
that is inexpensive to manufacture and maintain while retaining its 
effectiveness. 
Further objects of the invention will be brought out in the following part 
of the specification, wherein detailed description is for the purpose of 
fully disclosing the invention without placing limitations thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings where the present invention is generally 
referred to with numeral 10, it can be observed in FIG. 1 that it includes 
a cylindrical adapter casing 20 with a light emitting diode 30 on its 
upper surface 25 and a reset switch 40. Circuit 50 shown in FIG. 2 is 
housed within casing 20. Adapter casing 20 has a diameter that is 
sufficiently large to allow a snug fit over a conventional round fuse cap 
C. Fuse cap C has to be of the type that includes a transparent window 
element W that visually exposes fuse element F. Circuit 50 shown in FIG. 2 
is comprised of basically four sub-circuits or assemblies plus a battery 
assembly 60 feeding them. 
Photoelectric sub-circuit 70 includes a photosensitive element 75 that is 
characterized by changing its internal resistance when exposed to light. 
In the preferred embodiment, an MRD920 light-activated SCR, Radio Shack's 
catalog No. 276-1085A was used to implement the function of the 
photosensitive element 75. Element 75 is connected in series with 
resistive element 77 and the Vcc voltage of battery assembly 60 is apllied 
across the series combination so that a certain suitable voltage division 
is achieved at point P, giving voltage V.sub.PL when element 75 is exposed 
to light and V.sub.PN when there is no light. Point P is connected to 
latching sub-circuit 80 which comprises, primarily, of integrated circuit 
82 which in the preferred embodiment corresponds to a TLC 555 chip 
manufactured, among others, by National Semicondutors. An RC network is 
applied to the inputs of integrated circuit 82 to provide a suitable time 
constant for the bistable flip flop configuration of integrated circuit 
82. When light is applied to element 75, point P comes to voltage V.sub.PL 
which is connected to input pin 2 of integrated circuit 82 and adequate to 
activate integrated circuit 82 producing a logic 1 (high) or positive 
voltage at output pin 3. The output will stay positive at pin 3 for as 
long as the enabling voltage at P is V.sub.PL. To reset it, switch 
(normally open) 40 needs to be closed discharging capacitor 86 through 
resistor 84. 
The output of pin 3 in integrated circuit 82 is connected to the input 7 of 
integrated circuit 92 in oscillator sub-circuit 90. Integrated circuit 92 
is identical to integrated circuit 82 but wired as an astable 
multivibrator (flip-flop) with capacitive element 96 and resistive element 
94, which provide a suitable RC time constant that produces an oscillating 
signal with a relatively low duty cycle at output pin 3 of integrated 
circuit 92. It has been observed that a duty cycle of as low as 1.5 
percent with a Vcc voltage of 3 volts has been sufficient to drive LED 
sub-circuit 100 and providing enough energy to LED device 30 to create a 
visual indication. In the preferred embodiment, however, a duty cycle 
between 1.5 and 4.0 percent has been utilized to achieve the best 
compromise between insuring a visual indication and obtaining battery 
energy savings. This way, the battery energy savings are obtained by using 
a low duty cycle plus an intemittent indication. 
The circuit of FIG. 2 is housed within adapter casing 20 (FIG. 1) in such a 
way that photoelectric sub-circuit 70, and more particularly, 
photosensitive element 75, is aligned with fuse element F of conventional 
cap C when device 10 is mounted thereon. When fuse element F is blown, 
photosensitive element F sees the spark created, triggering integrated 
circuit 82 so that an enabling signal is applied to integrated circuit 92 
thereby sending low duty cycle pulses with just enough energy to produce a 
visual indication on LED element 30. 
It is believed the foregoing description conveys the best understanding of 
the objects and advantages of the present invention. Different embodiments 
may be made of the inventive concept of this invention. It is to be 
understood that all matter disclosed herein is to be interpreted merely as 
illustrative, and not in a limiting sense, except as set forth in the 
following appended claims.