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TECHNICAL FIELD OF THE INVENTION
The technical field of the invention is wall-mounted timers which turn off
associated loads after a prescribed interval of time.
BACKGROUND OF INVENTION
The subject matter of the invention is a delay switch whereby electrical
loads, such as electric lights controlled by a wall-mounted light switch,
may be turned on either to remain on indefinitely, or alternatively to
turn off after the elapse of a predetermined period of time as measured
from the instant of switch actuation. Such devices in one form or another
are long known in the art, and have proven themselves to be quite useful
in automatically turning off such electrical loads as, for example, garage
lights. In such situations the garage lights are turned on for a period of
time while the operator is leaving the house to enter his car and drive
off, the light automatically shutting down after a predetermined period of
time. Alternatively, such timers find similar applications in lighting
circuits, wherein the user actuates the timer to an automatic delayed
power-off condition when he knows that he will be leaving the room with
his arms encumbered, as a consequence of which he will be unable to turn
the light switch off by hand.
A variety of timers are known in the art. Thus, for example, U.S. Pat. No.
4,002,925 issued to Monahan discloses a wall receptacle-mounted timer
having a single toggle switch extending through a front mounting plate,
the switch being actuatable to a variety of positions and providing not
only delayed power-off, but also a delayed power-on feature as well.
Because of the provision for a delayed power-on feature, the number of
necessary switch positions is accordingly increased. The Monahan system
suffers from the disadvantage that it cannot be inserted directly into the
existing hot line wiring, but requires access to the low side of the line
as well so as to provide power for an associated power supply used to
power the timing circuitry, the supply being connected at all times across
the power lines. Thus, to apply the Monahan system to existing wiring, an
additional wire must be brought up to the conduit to the wall receptacle
box. Morever, since the power supply in always on, there is a constant
expenditure of power by the system, and as stated above, it is considered
a desirable feature to eliminate all such parasitic power losses when the
timing system is not operating in timing mode.
A related approach is disclosed in U.S. Pat. No. 4,336,464 issued to Weber,
which discloses a timer insertable directly into the hot line without
requiring access to the low (common) line, and which further shows a
load-energized power supply deriving its current from the hot line without
requiring connection to the low line. It therefore has the direct
insertion feature previously described as desirable; however, no provision
is made for turning off this power supply and the concomitant power
consumption when the associated electrical load is driven in a
conventional power-on condition, this power loss being present in both the
power-on and timer-on modes of the system. Thus, an additional energy
wastage is encountered. Additionally, the Weber system requires a pair of
independent switches and does not show the desirable feature of a single
actuating switch.
Thus, the prior art does not show in any one embodiment a simple time delay
three-position wall mountable switch configured for direct replacement of
conventional wall-mounted toggle switches and having associated timing
circuitry which can be powered solely by access to the hot line to the
load, and which draws no parasitic power whatever except when specifically
actuated to the timing mode. Such a device would constitute a new, useful,
and non-obvious contribution to the art.
SUMMARY OF INVENTION
According to the invention, a simple power-off timing circuit is configured
to be mounted as an assembly in a conventional wall switch plate
receptacle, and is selectively actuatable by a single three-position
switch to a power-on, a power-off, and a timer-on condition, wherein the
unit remains in a power-on condition for a preset period of time after
actuation thereto, thereafter reverting to a power-off state. In contrast
to the Monahan system, the timing circuit and its associated power supply
are completely disconnected from the power lines except during the limited
period of operation of the timer in its active phase. Moreover, the timer
can be connected directly to the "hot" wire of the power line to which a
conventional switch is normally connected, without requiring feeding the
common side of the line to the timer. Only a single switch is employed,
and no power supply current is required while the switch is in the regular
power-on condition, in contrast to the Weber system. The number of
necessary parts is held to an absolute minimum, and a substantial measure
of circuit simplicity in cost economy is achieved by using the
self-resetting feature of a commonly available integrated circuit timing
chip.
Additionally, the assembly is designed to match with the customary toggle
accepting slotted front cover plate used in conjunction with conventional
wall switch box assemblies, so that no modification of an existing wall
plate is necessary, the entire assembly using existing standard, the
actuating switch handle of the timer being configured to fit through the
vertically oriented slot of view cover plate to be actuated in a vertical
direction, but having three stable positions, as contrasted with the
normal two position assemblies.
The above described invention is to be contrasted with the teachings of
U.S. Pat. No. 4,349,749 issued to Goldstein, et. al. This patent discloses
a complex programmable timer wherein the user sets various intervals of a
24 hour period to be automatically switched on or off. To this end, an
internal timer circuit must always be in operation, since it carries a
representation of the present time of day. This kind of timer, unless
manually repeatedly overridden continues to cycle loads, such as light on
and off automatically during various preset intervals. This patent does
not in any case show the simple feature whereby at any time an operator,
simply by flipping a switch, may initiate an elapsed time actuation of a
remote device without going through a series of elaborate reprogramming
steps. Moreover, this timer fails to accomplish another feature of the
present invention, namely power economy.
U.S. Pat. No. 4,096,542 issued to Pappas et. al. discloses a timer which
performs some of the features of the present invention, but performs them
in an inverse order to that desired, in that this system turns a timer on
automatically at a preset time and thereafter turns off an associated
device solely by means of sensing a decrease in the associated system
load. As contrasted to the present invention, the objectives are
completely opposite; the timer of the present invention is turned on
manually to remain in such condition for a fixed period of time
thereafter, and is moreover configured to remain in such configuration
quite irrespective of any variation of the system load. Thus the timer of
the present invention will function perfectly well under widely varying
current conditions to the system load, e.g. high motor start-up currents
followed by lower sustaining currents. Moreover, the Pappas system
apparently needs a constant supply of direct voltage for a power supply to
allow the sensing amplifiers to respond to a timer-on signal. Thus,
additional power dissipation from the power mains is incurred during
power-off conditions, whereas a feature of the present invention is that
such power consumption is present solely while the timing system is in its
active phase, to be totally disconnected thereafter.
Other features and advantages of the present invention will be apparent
from the following more particular description of the invention. The
accompanying drawings, listed hereinbelow, are useful in explaining the
invention.
DESCRIPTION OF DRAWINGS
FIG. 1 shows in schematic block diagram form a power control circuit of the
present invention used to control electrical power supplied from a source
to a load, the actuation of the control circuit being governed by an
interposed three position switch;
FIG. 2 is an expanded schematic view of the elements of FIG. 1, showing in
particular the internal circuitry of the power control circuit of FIG. 1;
FIG. 3 is an exploded view of a preferred embodiment of the power control
circuit and three-position switch of FIG. 1 configured to be assembed into
a box having a control switch extending outwardly therefrom; and
FIG. 4 is an exploded view showing the insertion of the box of FIG. 3 into
a standard wall mounted switch box, and having an associated covering face
plate mounted thereon.
DESCRIPTION OF INVENTION
As shown in block diagram form in FIG. 1, a switch timer is used to control
power to a pair of a.c. lines M--M powering load 11. More specifically,
line 44 represents a line (typically already installed in wiring conduit)
leading from a wall-mounted switch box (See FIG. 4) to the load 11 to be
controllably actuated. Line 44 connects to one input control line 30' of
the switch timer via a connector 33. Similarly, the remaining line 41 goes
directly to system mains, and is connected to the other input control line
32 via a connector 33'.
It is desired that the load 11, as for example a light, be optionally
automatically turned off after a predetermined time period after switching
it on. For this purpose there is provided a three-position switch 12,
which can be actuated by movement of the pole 14 to a "timer" position
contacting contact 15, an "off" position contacting contact 16, and an
"on" position contacting contact 17. When the switch 12 is actuated to the
"on" position, there is a direct circuit connecting the load to the power
lines M--M, and in this case the switch acts exactly like a single
pole-single throw switch currently found in standard wall fixture. When
the pole is moved to the "off" position, there is no complete circuit to
the load, and no energy is supplied therethrough. When the pole 14 is
moved to the "timer" position, the load circuit is completed through a
power control circuit 18, this circuit having the property of presenting a
very low impedance across switches 15 and 17 while the timer is on, and
thereafter presenting an extremely high impedance.
The overall functioning of the control circuit 18 is shown in block diagram
form. A power triac circuit 19 is connected between switch contact 15 and
17 so that when the switch 12 is turned to the "timer" position wherein
pole 14 makes contact to contact 15 the power triac circuit serves as a
controllable switch through which the current passes to the load. A triac
trigger circuit 20 controls the power triac circuit selectively to put it
either in conductive or nonconductive mode, and the timer circuit 21 is
provided to act as a control for the triac trigger circuit. The power
supply circuit 22 derives its output voltage from the voltage drop across
the power triac circuit 19 to supply power to the timer circuit 21.
Referring now to the detailed schematic circuit shown in FIG. 2, it will be
noted that the immediate effect of throwing switch S12 to the timer
position wherein pole 14 contacts terminal 15 alternating voltage from the
means M--M when applied to lines 30 and 32 respectively. Across these
lines are connected a power triac T1, a triac trigger circuit consisting
of a series connected string of elements consisting of trigger triac T2,
Zener diode Z1 having its anode connected to triac T2, and a resistor R1
completing the series string to line 32. Resistor R1 is nominally of 10
ohms, and the Zener diode Z1 has a nominal value of 10 volts breakdown,
and as will subsequently be shown, this diode serves as a voltage
regulating element for those elements comprising the power supply 22 of
FIG. 1. Similarly disposed across the power lines and running from line 30
to line 32 are the principal elements of the power supply 22, consisting
of a resistor R2 of nominal value 10,000 ohms, this resistor feeding the
cathode of a diode D1, the diode D1 in turn feeding a parallel capacitor
pair C1 and C3, the other end of the capacitor pair being coupled to the
cathode of diode D2, the anode of D2 finally being connected to line 32 as
will be discussed in more detail subsequently.
The remaining elements of FIG. 2 shown to the right of the power supply
elements just described constitute the elements of the timer circuit 21 of
FIG. 1, the details of which will subsequently be discussed in detail. At
this point, only the broad features need be outlined.
The central element of the timer is a programmable commercially available
integrated circuit timer 31 having the property that it is reset to an
initial timing condition upon application of power thereto, the timer then
placing its output at pin 8 in a high state to remain there until the
elapse of a predetermined time set by a charging network, at the end of
which time the timer automatically goes into a disabled state, placing its
output in a low state. The figure reference numbers 1, 2, 3, and 8 shown
with respect to the integrated circuit 31 represent the actual pin
connections of the Motorola type MC14541B integrated circuit. Also, the
positive supply terminal A of timer 31 represents the common
interconnection of terminals 9, 12, 13, and 14 of this particular unit.
Terminal B of integrated cicuit 31 represents terminals 5, 6, 7, and 10 of
the Motorola circuit, and is the point where negative power supply voltage
is to be supplied. It will be seen from FIG. 2 that the junction of diode
D1 and capacitor C1 is connected to terminal A of integrated circuit 31,
via line 24, and that the opposite side of this capacitor is connected to
terminal B the line 25. The output terminal 8 is connected via line 26
through resistor R6 to drive the base of transistor Q1, the emitter being
returned to terminal B, and the collector being returned via resistor R7
to the trigger terminal of triac T2. Resistors R6 and R7 have nominal
values of 20,000 and 1,000 ohms respectively. A resistor R5 is connected
between terminal 8 of integrated circuit 31 to terminal A thereof.
The functioning of the circuit of FIG. 2 upon closure of the switch 12 to
the timer position 15 will now be considered in detail, with initial
consideration being mainly directed at the power supply. Immediately
before closure, the capacitor pair C1-C3 is in a bled-down condition as a
result of a variety of leakage paths through the integrated circuit 31, as
well as to through the resistors R5 and R6, and the emitter of transistor
Q1. Immediately upon closure of switch 12, and upon the first positive
rise in voltage of line 30 with respect to line 32, since no power has
been supplied to the timer circuit via lines 24 and 25, accordingly output
terminal 8' of integrated circuit 31 is, low resulting in transistor Q1
being turned off. As a result of this, the trigger electrode of transistor
T2 is effectively floating, with the result that triac T2 is initially in
a nonconducting state.
As the positive voltage rises on line 30, capacitor C1 charges through the
string consisting of resistor R6 and diodes D1 and D2. The voltage across
capacitor C1 therefore begins to rise, ultimately reaching a value
sufficient to reset the timer element 31 to a reset condition, driving
output terminal 8' high and turning on transistor Q1, thereby pulling the
trigger electrode of triac T2 to a conducting potential, resulting in the
energization of this element to a conducting state. Whether this
energization occurs during the first positive half-wave of applied voltage
to lead 30 or after a series of positive half waves is immaterial; the
diodes D1 and D2 block capacitor C1 against discharge during the reverse
half cycles. It will, however, be noted that since transistor Q1 is on,
the potential of the end of resistor R7 tied to the collector of
transistor Q1 will be within less than 1 volt of the potential of the
integrated circuit local ground connected to terminal B, hence triac T2
will remain energized generally throughout all four quadrants of the full
voltage wave form applied to lines 30 and 32, triac triggering occuring
almost immediately upon each voltage axis crossing.
Thus, since triac TR1 may be viewed as being a conducting state at all
times after reset of the timer 31, thereafter on all positive excursions
of line 30 with respect to 32, capacitor C1 is charged through the low
impedence of triac T2 and the forward drop of diode D2. As these positive
excursions rise from zero, however, the Zener diode Z1 will fire at
approximately 10 volts of line potential, thereby largely pinning the
maximum voltage supplied to the capacitor C1 to approximately 10 volts. A
well regulated direct voltage therefore appears across the terminals of
capacitor C1 to supply power to the integrated circuit timer 31. The
charge on capacitor C1 is thus replenished on each positive excursion of
line 30 with respect to line 32. Moreover, when the Zener diode Z1 breaks
down, the series resistor R1 now undergoes a substantial current
therethrough, with the result that the trigger electrode of the main power
triac T1 is pulled via line 34 well away from the potential of line 32,
resulting in switching this triac to an on condition. This power triac T1
thus serves to provide the principal current carrying path to provide
current to the load 11. It will be noted, however, that during these
positive half cycles, this current is not provided until the voltage on
line 30 rises to approximately 10 volts above the potential of line 32. As
previously stated, during this interval the power supply circuit is
replenished, and the loss of power available to the load is relatively
trivial, the system being designed to operate from source voltages
provided by the power mains M--M being of the order of 110 volts or more.
Recalling that triac T2 energizes almost instantly upon each axis crossing,
it follows that during negative excusions of line 30 with respect to line
32, a substantial current flows through this triac via resistor R1 and
Zener diode Z1, which is now biased in the forward direction. Here again
the result is, as before, to raise the potential of the trigger electrode
of triac T1 is almost immediately again pulled away from the potential of
line 32 to energize this unit to a conducting condition, thus again
supplying power to the system load 11. After an elapsed time set by the
charging network R3, C2, connected to terminals 1', 2', and 3' integrated
circuit 31, the output 8' reverts to a low state to remain there until the
next reset operation, thereby de-energizing transistor Q1, and
de-energizing triac T2.
Under such conditions, however, although the charging of capacitor C1
through diodes D1 and D2 continues as before, the current through Zener
diode Z1 on breakover in the positive cycle is limited by the high 10,000
ohm value of resistor R2, as a result of which insufficient current flows
through resistor R1 to trigger the main power triac T1 on the forward
cycle. On reverse cycles, triac T2 again remaining in an open condition,
since no current flows through resistor R1 because of the blocking action
of diode D1. Thus, the main power triac T1 cannot fire and the load is
disconnected accordingly. Because of the built-in inability of the
integrated circuit 31 to revert to a reset condition until power is
removed from terminals A and B and is subsequently reapplied thereto, it
follows that the load is permanently shut down by the overall action of
the circuit, to remain in such condition until it is reactuated.
To reactivate the timer to initiate a new timing operation, the pole 14 of
switch 12 must be moved for a period of a second or so to either of the
two remaining positions 16 or 17. During such interval capacitor C1 will
bleed down by mechanisms as previously described. The integrated circuit
31 will thereafter be ready to initiate a new one-shot timing cycle upon
actuation of the rotor 14 to the timer-on position where it contacts pole
15 thereof. A varister V1 is provided across the system power leads 30 and
32 to provide a measure of surge suppression so as to protect the various
components of the power control circuit.
Considering the timing circuit based upon integrated circuit 31 in more
detail, it will be recalled that this circuit uses the Motorola MC14541B
unit, a low-power complementary metal-oxide-semiconductor integrated
circuit having the property that it is reset to an initial timing
condition upon each application of power. The timing period is set by the
values of resistors R3 and R4 and the value of capacitor C2. After
expiration of the timing period the output terminal 8' goes high. As
previously described, the terminal designations shown are in consonance
with the terminal designations of this particular unit as manufactured;
however, it will be evident to those knowledgeable in the art that a
variety of timing circuits may equally well be applied to provide a
similar one-shot output pulse, provided that provision is made that the
output goes to a temporary first state for the duration of a timing period
after intial application of power to the timer, and provided that at the
expiration of said timing period the output terminal reverts to a latched
second state to remain there until power is removed from the timer and
subsequently applied thereto. This latching feature is central to the
operation of the circuit as describe herein.
FIG. 3 shows a preferred embodiment of the circuit of FIG. 2 adapted to be
mounted in a standard wall switch receptacle, the unit consisting of a
circuit board 28 carrying thereon the elements of the power control
circuit 18 of FIGS. 1 and 2. A face plate 34 carries the three position
switch 12 of FIGS. 1 and 2 mounted thereon and having a forwardly
projecting associated actuated handle 12', the handle being disposable to
center, upper, and lower positions respectively corresponding to a
selective contact to contacts 15, 16, and 17 of the switch. In the
embodiment shown in FIG. 3, the switch S12 (not shown) is contained within
a rearwardly extending housing 36 mounted to the panel 34 preferably by
conventional front-insertion snap-in means (not shown) of a type
frequently provided on commercially available faceplate-mounted switches,
the switch housing extending rearwardly from the panel 34. The housing 36
is fixedly attached to the circuit board 28 to provide support therefor.
This attachment may be by variety of means, most preferably by fastening
the circuit board 28 to the rear of the switch housing 36 either by means
of screw terminals (not shown) passing through the circuit board from the
rear, or alternatively by solder lugs (not shown) extending rearwardly
from the switch housing 36 and passing through appropriate openings in
circuit board 28 to be fastened thereto by conventional means, e.g. by
soldering to adjacent metallization paths on the circuit board itself. The
assemby 40 shown in FIG. 3 is held together by screws 42 extending
rearwardly through the front panel 34 via clearance holes 43 therein and
into threaded screw holes 44 in the box 27. The power leads 30' and 32
shown in FIGS. 1 and 2 are seen exiting from holes in the circuit board 28
to exit the housing 27 from the rear as indicated.
FIG. 4 shows the completed control circuit assembly 40 positioned for
insertion into a conventional wall switch receptacle 27a, the power leads
30' and 32 thereof being connected to conventional power switching lines
44--44 via connectors 33--33. A face plate 35 is provided bearing the
legends "ON", "OFF", and "TIMER" placed to one side of a matching cut-out
50 configured to accept the outwardly extending switch handle 12' of the
power unit 40. The entire assembly is secured to the wall receptacle box
27a by means of screws 45--45 passing through clearance holes 52 in the
cover plate 35, clearance holes 54 in the front plate 34 of the assembly
40, and threadingly engaging holes 48 in the wall mounted switch box 27a.
It will be noted that the switch is of the vertically actuated toggle
type, and is configured to fit a standard face-plate vertical slot
cut-out.
Thus, there has been described a simple power-off timing circuit configured
to be mounted in a conventional wall switch plate receptacle, and
selectively actuatable by a single three-position switch to a power-on, a
power-off, and a timer-on condition. Moreover, in contrast to the Monahan
system cited in the Background of the Invention, the timing circuit and
its associated power supply are completely disconnected from the power
lines except during a limited period of operation of the timer in its
active phase, and can be connected directly to "hot" wires of the power
line to which a conventional switch is normally connected, without
requiring feeding the common side of the line to the timer. In contrast to
the Weber system mentioned in the Background of Invention, only a single
switch is employed, and no power supply current is required while the load
is in the regular power-on condition. The number of necessary parts is
held to an absolute minimum, a substantial measure of circuit simplicity
and cost economy being achieved by using the self-resetting feature of a
commercially available integrated circuit timing chip.
While the invention has been described with reference to a preferred
embodiment, it will be understood by those skilled in the art that various
changes may be made and equivalents may be substituted for elements
thereof without departing from the scope of the invention. In addition,
many modifications may be made to adapt a particular situation or material
to the teachings of the invention without departing from the essential
scope thereof. Therefore, it is intended that the invention not be limited
to a particular embodiment disclosed as the best mode contemplated for
carrying out the invention, but that the invention will include all
embodiments falling within the scope of the appended claims.
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