U.S. patent number 3,790,848 [Application Number 05/242,351] was granted by the patent office on 1974-02-05 for automatic light control system.
Invention is credited to Thomas K. Y. Lai.
United States Patent |
3,790,848 |
Lai |
February 5, 1974 |
AUTOMATIC LIGHT CONTROL SYSTEM
Abstract
Garage lights are automatically turned on by a photocell which
is illuminated by automobile headlights. A timing circuit keeps the
lights on for a predetermined period after automobile headlights
are turned off. House current is stepped down, rectified and
smoothed. Direct current is applied across a variable voltage
divider. A starter which may be a push button, a headlight
receiving photocell or a roll over switch supplies voltage to a mid
point of the divider. Voltage at the mid point is reduced during
daylight hours by an exterior photocell in a conductive condition.
During darkness the exterior photocell's high resistance as
compared to the low resistance of a headlight actuated photocell
creates a high mid point voltage. The high mid point voltage breaks
down a zener diode, gating current to a capacitor and biasing an
electronic switch for turning on the garage lights. When the
voltage applied to the breakdown device falls, the gate turns off,
and the capacitor slowly discharges through a resistor. A
directional limiting device in the gate and cascaded transistors in
the switch biasing connection prevent discharge of the capacitor
except through the desired resistor. The electronic switch employs
cascaded transistors for controlling the application of direct
current to a reed relay. Power contacts of the relay complete a
diac circuit, which biases on a triac, turning on the lights.
Inventors: |
Lai; Thomas K. Y. (Honolulu,
HI) |
Family
ID: |
22914443 |
Appl.
No.: |
05/242,351 |
Filed: |
April 10, 1972 |
Current U.S.
Class: |
315/155;
250/208.4; 315/159 |
Current CPC
Class: |
H03K
17/292 (20130101); H05B 47/10 (20200101) |
Current International
Class: |
H03K
17/28 (20060101); H03K 17/292 (20060101); H05B
37/02 (20060101); H05b 037/02 (); H05b 039/04 ();
H05b 041/36 () |
Field of
Search: |
;315/155,159
;250/209 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Grigsby; T. N.
Attorney, Agent or Firm: Wray; James C.
Claims
1. A lighting system comprising a power source, light means for
illuminating a space, and control means for communicating the power
source with the light means, the control means comprising a
breakdown device having a first terminal and having a second
terminal connected to ground, a first resistance connected between
the first terminal and ground, resistance reducing means connected
in parallel to the first resistance, an exterior photocell for
sensing daylight conditions connected to the reducing means and for
activating the reducing means, thereby maintaining a circuit
through the breakdown device in the control means open during
daylight conditions, a controller connected to the power source and
to the first terminal for completing the circuit in the control
means from the power source through the breakdown device when the
controller is activated and when the exterior photocell is inactive
during darkness, and switch means connected to the circuit and
connected to the power source and to the light means for
communicating the power source and the light means
2. The lighting system of claim 1 further comprising energy storage
means connected to the circuit and energy drain means connected to
the circuit in parallel to the energy storage means between the
switch means and the second terminal of the breakdown device for
maintaining operation of the circuit and the switch means while
energy is stored in the storage means and for terminating operation
of the circuit and switch means when energy
3. The lighting system of claim 1 wherein the power source
comprises a source of alternating current, and wherein the light
means comprises electric lamps operable upon communicating with the
power source, and wherein the control means comprises a power
supply connected to the power source for converting the alternating
current to direct current and a voltage divider connected to the
power supply, wherein the exterior photocell is connected between a
midpoint and ground in the voltage divider, and wherein the
breakdown device is connected to the midpoint, whereby light
impinging on the exterior photocell reduces voltage of the midpoint
below a breakdown voltage, and whereby the exterior photocell
presents a high resistance during darkness, and whereby the
controller reduces resistance in the opposite portion of the
voltage divider so that voltage of the midpoint is raised to exceed
breakdown voltage of the breakdown device, and wherein the switch
means comprises electronic switch means having a control terminal
connected to the breakdown device and having power terminals
connected between the power source and the light means whereby
voltage at or above breakdown voltage passes through the breakdown
device to the control terminal, operating the switch, completing
the power terminals and communicating the power source and the
light
4. A timed automatic lighting system for providing illumination
during passage between automobile and house doorways comprising a
power supply having a primary with terminals configured for
connection to a household power source and having a secondary for
reducing primary voltage, rectifier means connected to the
secondary for producing direct current, a starting circuit
connected to the rectifier and having a starter for passing varied
current according to a condition of the starter, and shorting means
connected to the starting circuit and to the rectifier for
substantially shorting the starting circuit, the shorting means
comprising a first resistance connected between the starter and
ground, resistance reducing means connected in parallel to the
first resistance, and an exterior photoresistor connected in the
resistance reducing means for reducing resistance and shorting the
starting circuit when the exterior photoresistor is illuminated by
daylight, gating means comprising a breakdown device having a first
terminal connected to the starting circuit for gating current above
a predetermined voltage, timing means comprising a capacitor and
resistor connected in parallel between ground and a second terminal
of the breakdown device and thereby connected to the gating means
for receiving current from the gating means, and a switch means
connected to the timing means for closing when the timing means is
on, transmission means connected to the switch means and having
terminals for connection to a household power source and light
producing means connected to the transmission means, whereby the
light means are lighted when the switch
5. The lighting system of claim 4 wherein the timing means
capacitor and resistor, comprises storage means for storing energy
from the gating means, and comprises discharge control means
connected to the storage means for controlling discharge rate of
the storage means upon interruption of gated energy, whereby the
switch means is held on for a
6. The lighting system of claim 4 wherein the shorting means
comprises a transistor having power terminals communicating with
the starting circuit and with ground and wherein the external
photoresistor is connected to a base of the transistor for turning
the transistor on during daylight
7. A lighting system comprising a source of alternating current,
electric lamps operable upon communicating with the source for
illuminating a space, a power supply connected to the power source
for converting the alternating current to direct current, a voltage
divider connected to the power supply, an exterior photocell
connected between a midpoint and ground in the voltage diver, a
breakdown device is connected to the midpoint, whereby light
impinging on the exterior photocell reduces voltage of the midpoint
below a breakdown voltage, and whereby the exterior photocell
presents a high resistance during darkness, a controller connected
between the midpoint and an opposite pole of the voltage divider,
whereby the controller reduces resistance in the opposite portion
of the voltage divider so that voltage of the midpoint is raised to
exceed breakdown voltage of the breakdown device, an electronic
switch means having a control terminal connected to the breakdown
device and having power terminals connected between the power
source and the lamps whereby voltage at or above breakdown voltage
passes through the breakdown device to the control terminal,
operating the switch, completing the power terminals and
communicating the power source and the lamps, a capacitor connected
to ground and to a point in the circuit between the control
terminal of the switch means and the breakdown device for storing
energy passing through the device and a discharging resistor
connected in parallel to the capacitor for slowly discharging the
capacitor, whereby upon discontinuance of operation of the
controller, and hence discontinuance of the breakdown voltage and
discontinuance of current passing through the breakdown device, the
capacitor maintains the control terminal at a voltage sufficient to
hold the electronic switch means on for a period of time until the
resistor discharges the capacitor to a
8. The apparatus of claim 7 further comprising a filter connected
across the power supply and parallel to the voltage divider, a
current limiting resistor connected in series between the power
supply and the voltage divider, and a zener diode connected in
parallel to the filter, whereby voltages in excess of a breakdown
voltage of the zener diode are grounded.
9. The lighting system of claim 7 wherein the circuit further
comprises a reverse current preventing device inserted between the
breakdown device and the capacitor for preventing discharge of the
capacitor through the breakdown device, and wherein the electronic
switch means further comprises a high input-resistance cascaded
transistor device connected to the control terminal for preventing
discharge of the capacitor through the
10. A timed automatic lighting system for providing illumination
during passage between automobile and house doorways comprising a
power supply having a primary with terminals configured for
connection to a household power source and having a secondary for
reducing primary voltage, rectifier means connected to the
secondary for producing direct current, a starting circuit
connected to the rectifier having a starter comprising a penumatic
pulse operated switch for passing varied current according to a
condition of the starter, and shorting means connected to the
starting circuit and to the rectifier for substantially shorting
the starting circuit, gating means connected to the starting
circuit above a predetermined voltage, timing means connected to
the gating means for receiving current from the gating means, and
switch means connected to the timing means for closing when the
timing means is on, transmission means connected to the switch
means and having terminals for connection to a household power
source and light producing means connected to the transmission
means, whereby the light means are lighted when the switch
11. The lighting system of claim 10 wherein the pneumatic pulse
operated switch comprises an air hose plugged at a distal end and
connected to a nipple communicating with a base of a first cup, a
second cup inverted upon the first cup and slidable thereon, and
contacting means connected to the second cup, whereby the second
cup is slid outward and the contacts
12. A timed automatic lighting system for providing illumination
during passage between automobile and house doorways comprising a
power supply having a primary with terminals configured for
connection to a household power source and having a secondary for
reducing primary voltage, rectifier means connected to the
secondary for producing direct current, a starting circuit
connected to the rectifier having a starter comprising a photocell
and a variable resistor connected in series for passing varied
current according to a condition of the starter, and shorting means
connected to the starting circuit and to the rectifier for
substantially shorting the starting circuit, gating means connected
to the starting circuit above a predetermined voltage, timing means
connected to the gating means for receiving current from the gating
means, and switch means connected to the timing means for closing
when the timing means is on, transmission means connected to the
switch means and having terminals for connection to a household
power source and light producing means connected to the
transmission means, whereby the light means are lighted when
the
13. The lighting system of claim 12 further comprising a push
button
14. A lighting system comprising a source of alternating current,
electric lamps operable upon communicating with the source for
illuminating a space, a power supply connected to the power source
for converting the alternating current to direct current, a voltage
divider connected to the power supply, an exterior photocell
connected between a midpoint and ground in the voltage divider, a
breakdown device is connected to the midpoint, whereby light
impinging on the exterior photocell reduces voltage of the midpoint
below a breakdown voltage, and whereby the exterior photocell
presents a high resistance during darkness, a controller connected
between the midpoint and an opposite pole of the voltage divider,
whereby the controller reduces resistance in the opposite portion
of the voltage divider so that voltage of the midpoint is raised to
exceed breakdown voltage of the breakdown device, an electronic
switch having a control terminal connected to the breakdown device,
and having a reed relay, the reed relay having power contacts, a
diac connected in series to the power contacts and to the power
source, a triac having power terminals connected to the lamps and
to the power source and having a control terminal connected to the
diac for supplying power from the source to the lamps upon
completion of the diac circuit by closing of the reed
15. A lighting system comprising a source of alternating current,
electric lamps operable upon communicating with the source for
illuminating a space, a power supply connected to the power source
for converting the alternating current to direct current, a voltage
divider connected to the power supply, an exterior photocell
connected between a midpoint and ground in the voltage divider, a
breakdown device is connected to the midpoint, whereby light
impinging on the exterior photocell reduces voltage of the midpoint
below a breakdown voltage, and whereby the exterior photocell
presents a high resistance during darkness, a controller connected
between the midpoint and an opposite pole of the voltage divider
wherein the controller compr1ses a second photocell and a normally
open push button connected in parallel whereby the controller
reduces resistance in the opposite portion of the voltage divider
so that voltage of the midpoint is raised to exceed breakdown
voltage of the
16. A lighting system comprising a source of alternating current,
electric lamps operable upon communicating with the source for
illuminating a space, a power supply connected to the power source
for converting the alternating current to direct current, a voltage
divider connected to the power supply, an exterior photocell
connected between a midpoint and ground in the voltage divider, a
breakdown device is connected to the midpoint, whereby light
impinging on the exterior photocell reduces voltage of the midpoint
below a breakdown voltage, and whereby the exterior photocell
presents a high resistance during darkness, a controller connected
between the midpoint and an opposite pole of the voltage divider,
wherein the controller comprises an air hose operated pneumatic
roll over switch and a push button connected in parallel, whereby
the controller reduces resistance in the opposite portion of the
voltage divider so that voltage of the midpoint is raised to
exceed
17. A timed automatic lighting system for providing illumination
during passage between automobile and house doorways comprising a
power supply having a primary with terminals configured for
connection to a household power source and having a secondary for
reducing primary voltage, rectifier means connected to the
secondary for producing direct current, a starting circuit
connected to the rectifier having a starter for passing varied
current according to a condition of the starter, and shorting means
connected to the starting circuit and to the rectifier for
substantially shorting the starting circuit, gating means connected
to the starting circuit above a predetermined voltage, timing means
connected to the gating means for receiving current from the gating
means, the timing means comprising storage means for storing energy
from the gating means, and discharge control means connected to the
storage means for controlling discharge rate of the storage means
upon interruption of gated energy, whereby the timing means is held
on for a predetermined time after interruption of the gated energy,
the discharge controlling means comprising a resistor connected in
parallel to the storage means, a unidirectional device connected
between the storage means and the gating means for preventing
reverse flow of current through the gating means, and base
connections to cascaded transistors for preventing flow of
substantial current through base circuits of the transistors; and
switch means connected to the timing means for closing when the
timing means is on, transmission means connected to the switch
means and having terminals for connection to a household power
source and light producing means connected to the transmission
means, whereby the light means are lighted
18. A timed automatic lighting system for providing illumination
during passage between automobile and house doorways comprising a
power supply having a primary with terminals configured for
connection to a household power source and having a secondary for
reducing primary voltage, rectifier means connected to the
secondary for producing direct current, a starting circuit having a
starter switch with normally open terminals, the starting circuit
being connected to the rectifier for passing varied current
according to a condition of the starter, the starting circuit
comprising a capacitor connected to the terminals for storing
current passing through the terminals, transistor mean having a
base connected to the capacitor adjacent the terminals, for turning
the transistor means on when the terminals are closed, and the
transistor means having power terminals in the starting circuit;
and shorting means connected to the starting circuit and to the
rectifier for substantially shorting the starting circuit, gating
means connected to the starting circuit above a predetermined
voltage, timing means connected to the gating means for receiving
current from the gating means, and switch means connected to the
timing means for closing when the timing means is on, transmission
means connected to the switch means and having terminals for
connection to a household power source and light producing means
connected to the transmission means, whereby the light means are
lighted when the switch means is closed.
Description
BACKGROUND OF THE INVENTION
Known garage light systems of the prior art have employed
mechanically operated switches which are held in an on position for
a long time in order to sufficiently activate a timing system to
delay an extinguishing of lights. Such systems have used heavy duty
wiring to heavy duty relays to control the switching on and off of
light circuits and timing devices. Generally, the timing systems
are expensive because of their requirement for heavy duty
compounds, and the systems are incapable of use with devices which
supply only a very short pulse of energy. For example, none of the
known fixed lighting systems employs small aimed photocells for
triggering by quick flashes of headlights.
SUMMARY OF THE INVENTION
The present invention is a light system which is used for
controlling lights in darkened areas usually outside a house or
apartment. Lights controlled by the present system are usually
those lights within a garage or those lights within passageways
between a parking space and residences. The purpose of the usual
application of the present invention is to provide temporary
lighting for darkened spaces while one is passing from a house to
an automobile or from an automobile to a residence.
In a preferred form the control of the present invention is
packaged in a single unit with two terminal boards. One terminal
board is a low voltage board to which the remote switching or
starting elements are connected. For example, a push button switch
near a doorway for starting a system as one leaves a house, a
headlight receiving photocell and an exterior daylight sensing
photocell may be connected through long, fine, low-voltage terminal
board. The household voltage power lines and the lighting circuits
are connected to the high-voltage terminal board.
In the preferred form of the invention, supplied voltage is reduced
and rectified. AC ripples are smoothed with a filter, DC current is
limited with a resistance, and voltage surges are grounded with a
breakdown device.
The substantially constant DC voltage is supplied to a voltage
divider. In the divider, an exterior photocell is connected between
mid point and ground. Resistance of the exterior photocell is
reduced during daylight hours, bringing mid point voltage closer to
ground potential.
Starters are connected in parallel between the mid point and a
point of maximum DC voltage. Usually the starters are a push button
near an entrance to a residence and a headlight sensing photocell
or roll over pneumatic impulse switch at a garage entrance. During
darkness hours when the resistance of the exterior photocell is
high, reducing resistance of any one of the starters raises the
potential of the mid point of the voltage divider closer to the
maximum DC voltage.
A gate is connected to the mid point. When potential of the mid
point in the voltage divider exceeds breakdown voltage of a
breakdown device in the gate, such as during darkness hours when
one of the starters is activated, the DC power is gated to
immediately charge a capacitor, turning a timer on. At the same
time, an electronic switch is turned on, completing the lighting
circuit and turning on the garage and passageway lights.
When the starter is deactivated, the timer keeps the lights on for
a time predetermined by the discharge rate of the capacitor. The
discharge rate is in turn controlled by the value of a resistance
which discharges the capacitor to ground. Discharge in a reverse
direction through the breakdown device gate is prevented is
prevented by a unidirectional element. Discharge through the
electronic switch is prevented by use of a cascaded transistor with
a high input resistance, for example, a Darlington transistor. If
varied timing is desired, the apparatus may be provided with varied
resistors connected in series or in parallel or with a variable
resistor to control timing. In a preferred embodiment, a single
resistor having a sufficiently high resistance to provide a slow
rate of discharge is provided so that lights are held on for a
number of minutes.
In a preferred embodiment of a light switch, a transistor is biased
on, completing the application of the full DC current to a reed
relay. Power contacts of the relay are connected in one side of an
AC voltage divider. The relay completes AC power to a diac which is
connected in the biasing circuit of a triac. Closing of the relay
contacts turns the triac on, completing the AC power circuit to the
lights.
While the present lighting system is described with particular
application to a system for turning on garage lights, the present
system is useful in any application where a timed power supply
capable of responding to an impulse input is useful.
One object of the present invention is the provision of a lighting
system which employs a timing system capable of responding to a
brief starting activation.
Another object of this invention is the provision of a garage
lighting system which employs a headlight sensing photocell
connected in combination with an exterior daylight sensing
photocell to turn on garage lights and associated passageway lights
during hours of darkness when the automobile headlights are
detected.
Another object of the invention is the provision of a lighting
system employing starting and sensing elements in a voltage divider
circuit to control gating of energy to turn on lights and to start
a timing circuit.
Another object of the invention is the provision of an electronic
switch for use in a lighting system.
This invention has as another object the provision of a variable
voltage dividing circuit and gate for use in an automatic lighting
system.
Another object of this invention is the provision of a
self-contained electronic control system for automatically turning
on and off garage lights.
These and other objects of the invention are apparent in the
specification, which includes the foregoing and ongoing
description, and the claims and from the drawings, which taken
together, comprise the disclosure of the invention, using one
preferred embodiment by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of the apparatus of the
present invention, showing the system with its boxed electronic
controls, the power source and electric light connections and the
remote controlling devices.
FIG. 2 is a schematic representation of the main elements of the
present invention.
FIG. 3 is a schematic diagram of the circuits of the present
invention, showing in detail the interrelated elements and the
terminal board connections of a preferred embodiment of the
invention.
FIG. 4 is a schematic drawing similar to FIG. 3 with a modified
shorting portion or lower portion of the voltage divider.
FIG. 5 is a schematic drawing of circuitry provided with an impulse
switch.
FIG. 6 is a detail of an air-operated impulse switch actuator.
DETAILED DESCRIPTION OF THE DRAWINGS
Throughout the drawings, like elements are referred to by like
numerals.
In FIG. 1, the numeral 1 generally indicates the light control
system of a preferred embodiment of the present invention. Electric
light 2 represents a lighting circuit which is controlled by the
automatic device of the present invention. Plug 4 is representative
of a connection for a power source. Box 6 contains the electronic
circuits of the present invention and terminal boards.
Photocell 8 is mounted on an exterior of a building, for example, a
garage to prevent operation of the system during daylight hours.
Photocell 10 is mounted within a garage to detect headlights of
cars for starting the system when a car is parked in a garage. In a
two-car garage, photocell 10 may be centrally mounted to detect
headlights from either car. Photocell 10 may be used with
adjustable circuits to detect back up lights when automobiles are
backed into a garage.
In some cases, such as in drive-through carports, no wall is
available for mounting of an interior photocell. A pneumatic switch
12 may be substituted for photocell 10. Closed air hose 14 supplies
a pulse of air to switch 12 as an automobile crosses the hose. It
is convenient to mount a push button starter 16 adjacent a
pedestrain entry to the garage. Where more than one entry to a
garage is commonly used in darkness hours, two or more push buttons
16 may be connected in parallel.
As shown schematically in FIG. 2, exterior photocell 8 and interior
photocell 10 are connected in a variable voltage divider 20. When
darkness turns photocell 8 off and headlights turn photocell 10 on,
a potential is provided to voltage gate 22 which is sufficient to
breakdown device 24 and gate current to timer circuit 30.
Unidirectional device 26 in gate 22 prevents reverse flow of
current from timer 30.
Timer circuit 30 contains a capacitor 32 and a resistance 34 which
discharges the capacitor. When the potential is gated to the timer
circuit 30 and during the time that capacitor 32 maintains a
sufficient potential, light switch 36 is held on. Triac 38 is
schematically shown within the light switch 36 for controlling lamp
2.
Power supply 40 receives power from source 4, transmits the power
to the light switch, and reduces and rectifies current which it
supplies to the variable voltage divider, the gate and the timer
circuit.
In FIG. 3 a low voltage terminal board generally indicated by TB1
has connections A through F which are found in the upper part of
the figure. High voltage terminal board TB2 has connections A, B
and C which are shown in the upper part of the drawing as, for
example, TB2-A. Terminals A and B on the high voltage board are
connected to lamps 2, and terminals B and C are connected to a
voltage source which is shown as a plug 4. In systems which are
intended for use in new constructions, lamps 2 generally indicate
the basic garage lights, and source 4 is wired directly to the
roughed in electrical wiring. In add on systems a plug 4 and power
lines are supplied. Lamps 2 may be the existing lamps, or
externally wired lamps may be provided with a kit.
On the low voltage terminal board TB1, contacts A and B receive the
push button. Terminals C and D receive the internal photocell 10 or
roll over switch 12, or both may be connected in parallel to
terminals C and D. Terminals E and F receive low voltage wiring
from the external photocell 8.
Referring to the main circuit in FIG. 3, voltage is supplied at
source 4. A fuse 42 protects the circuit against voltage surges,
which may be caused externally or by a short circuit in the system.
Household current is applied through fuse 42 to primary 44 of
transformer 46. Secondary 48 reduces the voltage to approximately
12 volts AC. A bridge rectifier generally indicated by the numeral
50 and comprising diodes 52, 54 56 and 58 changes the low AC
voltage to low DC voltage. Capacitor 60 filters AC components and
smooths the output of the rectifier. Current limiting resistor 62
limits the current flowing through the DC electronic components.
Zener diode 64 breaks down at 12 volts, effectively shorting
voltage surges and insuring that voltage between positive power
line 68 and ground 70 does not exceed 12 volts.
In the variable voltage divider 20, photocells 8 and 10 may have
dark resistances of about 5,000 ohms, or more, which are reduced to
about 500 ohms when illuminated. 15K ohm resistor 72 is connected
in parallel to photocell 8 in the lower portion of the divider so
that the combined resistance of photocell 8 and resistor 72 is
below 500 ohms when external photocell 8 is illuminated during
daylight hours. In daylight conditions, the potential of mid point
80 is thus reduced toward ground potential. In the upper portion of
the divider, light cell 10 is connected in series with variable
resistor 74, which has a capacity of about 25K ohms. Adjustment of
resistor 74 is made to bring the mid point 80 to a potential above
the breakdown voltage of the breakdown device 24 in gate 22. When
12 volts are imposed across lines 68 and 70, resistor 74 may be
adjusted so that when photocell 10 is illuminated by headlights
during darkness hours, mid point 80 is brought to a potential
slightly above a breakdown voltage of 6.8 volts. Correctly
adjusting resistor 74 according to the fixed position of photocell
10 insures correct operation of the automatic system and insures
against starting of the system by spurious illumination of
photocell 10.
Photocell 10 may be replaced by an impulse switch 12 or other
suitable switch with a series connected resistance 76.
For convenience, one or more push buttons may be provided at
entrances to a garage. Preferably the push buttons are connected in
series with a resistor 78, which may have a value of about 470
ohms.
During daylight hours, the low resistance of photocell 8 and the
parallel resistor 72 will always keep mid point 80 below the level
of breakdown voltage required by breakdown device 24. When
photocell 8 imposes its high darkness resistance, the potential of
mid point 80 may be raised above the breakdown voltage by reducing
resistance in photocell 10 or by completing any of the
switches.
Gate 22 contains breakdown device 24 which is preferably a zener
diode. When voltage at mid point 80 exceeds breakdown voltage,
zener diode 24 conducts, supplying current to capacitor 32 and to
timer 30 and to electronic switch 36. Storage capacitor 32 is
charged immediately upon application of voltage to the timer
circuit. Resistor 34 discharges voltage from capacitor 32 after the
applied voltage has been discontinued. The rate at which resistor
34 discharges voltage from capacitor 32 controls the period of
timer 30. Discharge of capacitor 32 through voltage divider 20 is
prevented by unidirectional element 26 which is a diode. Discharge
of the timer through the light switch 36 is prevented by a high
input impedance device, in this case a Darlington transistor
84.
As an example, the capacitor 32 may have a value of 500
microfarads. Resistor 34 may have a value of from about 150 to
about 2 megaohms. Resistor 82 may have a value of about 1.5
megaohms. Resistors 90 and 92 may have resistances of about 10 K
ohms and 2.7 K ohms respectively. The function of the resistors 82,
90 and 92 and of the cascaded transistors 84 which may be comprised
of individually packaged transistors 86 and 88 is to forward bias
the light switch 36 while preventing substantial discharge of
capacitor 32.
When transistor 94 is biased on by voltage from the timer section
30, DC power is supplied to reed relay 98 via current limiting
resistor 96. Power terminals 100 and 102 of reed relay 98 close,
completing the AC circuit to diac 104. Capacitor 106 and resistor
108 cooperate as an AC voltage divider so that the appropriate
potential is applied via diac 104 to the biasing terminal of triac
38. Power terminals of triac 38 complete the circuit between power
source 4 and lights 2.
As shown in FIG. 3, diode 99 protects the transistor 94 from sudden
surges when the field collapses in relay coil 98. At the same time,
diode 99 keeps the relay polarized.
FIG. 4 is a modified form of FIG. 3, in which the variable voltage
divider circuit is changed. The modification of FIG. 4 insures that
the system is held off during times of partial potential sensed by
the exterior photocell. With the exception of the change to the
voltage divider circuit, all of the elements of FIg. 4 are the same
as the elements and circuits of FIG. 3. Similar elements are
designated by similar reference numerals. In the upper half of the
voltage divider the elements and circuitry of FIG. 4 are similar to
the elements and circuitry of FIG. 3.
In the lower half of the voltage divider resistor 106 has the same
value as resistor 72 in FIG. 3. Resistor 106 is the only resistor
which is conductive during darkness hours. Consequently, the
potential of mid point 80 is held at a level sufficiently high to
breakdown device 24 for gating current to the timer.
During daylight hours, resistor 108, which has a value of about 100
ohms, is grounded through transistor 110, effectively shorting the
high resistance element 106. Transistor 110 is turned on by raising
the value of its base connection 112 to an on voltage. The
potential of base connection 112 is established by a second voltage
divider which comprises resistor 114 and photocell 116. Resistor
114 has a value of about 150 ohms. Photocell 116 has a value of
about 5,000 ohms or more when dark and 500 ohms when illuminated.
Until photocell 116 resistance is raised to a point near 5,000
ohms, base 112 is held off.
The effect of the particular circuit of FIG. 4 is to bias
transistor 110 on, thereby effectively shorting resistance 106
during any light. When dark, photocell 116 biases transistor 110
off, cutting off the path to ground through resistor 108, and
grounding mid point 80 only through resistor 106.
When an air hose 14 is placed in such a position that a car rapidly
passes over the air hose, contacts in air switch 12 may be held
closed for a time insufficient to fully charge the timer 30. To
provide sufficient charging of timer 30, a circuit such as shown in
FIG. 5 may be employed.
In the circuit shown in FIG. 5, capacitor 118 keeps the current on
for a sufficient time to charge the capacitor in timer 30.
As in FIGS. 3 and 4, air switch 12 is connected to terminals C and
D of the first low voltage terminal board 1. When air switch 12 is
activated, terminals 150 are closed, charging capacitor 118. The
capacitor 118 holds a charge and maintains a bias through resistor
120 on cascaded transistors 122 and 124. During the time that
contacts 150 are closed and the additional time in which capacitor
118 retains a charge, transistor 124 effectively shorts resistor
132 so that resistor 128 is the only resistance in the upper
portion of the voltage divider 20. That resistance is schematically
shown as resistor 76 in FIG. 3 and 4.
In one preferred embodiment, an air switch 12 comprises two
slidable plastic cups 134 and 136. Air is supplied to cup 136
through a central opening in base 138. The upper end 146 of hose 14
fits on nipple 142. The remote end of hose 14 is closed by plug 148
as shown in FIG. 5. The upper plastic cup 134 closes contacts 150
when it is lifted by air flowing from the hose.
The invention has been described in part by specific embodiments.
The function is not limited to those embodiments. Several
modifications may be made without departing from the scope of the
invention, which is defined in the following claims.
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