Location independent dimmer switch for use in multiple location switch system, and switch system employing same

A wall mountable dimmer switch for controlling the level of AC power delivered to a load, such as a lighting load. The switch is capable of being used as a single pole, three-way or four-way dimmer switch. The switch is responsive to signals supplied by auxiliary devices to increase, decrease or toggle on/off the power delivered to the load irrespective of the location of the switch when it is used in a multiple location switching system, and irrespective of the wiring of its hot and dimmed leads.

FIELD OF THE INVENTION 
The present invention relates to a wall mountable dimmer switch that can be 
wired for use in any location of a multiple location switch system without 
regard to the arrangement of the system wiring to the dimmer switch. The 
present invention also relates to a multiple location switch system 
employing such a dimmer switch. 
BACKGROUND OF THE INVENTION 
Three-way and four-way switch systems for use in controlling loads in 
buildings, such as lighting loads, have long been known in the art. The 
switches used in these systems are wired to the building's AC wiring 
system and are subjected to AC source voltage and carry full load current, 
as opposed to low voltage switch systems that operate at low voltage and 
low current and communicate low voltage commands (usually low voltage DC 
logic levels) to a remote controller that controls the level of AC power 
delivered to the load in response to the commands. Thus, as used herein, 
the terms "three-way switch", "three-way system", "four-way switch" and 
"four-way system" mean such switches and systems that are subjected to the 
AC source voltage and carry the full load current. 
In a three-way switch system, there are two three-way switches for 
controlling the load, e.g., one adjacent each passageway into the room, 
and each switch is fully operable to independently control the load 
irrespective of the status of the other switch. A four-way switch system 
is required when there are more than two switch locations from which to 
control the load. For example, a three switch system requires two 
three-way switches and one four-way switch, wired in well known fashion, 
so as to render each switch fully operable to independently control the 
load irrespective of the status of any other switch in the system. In the 
exemplary three switch system, the prior art requires the four-way switch 
to be wired between the two three-way switches in order for all switches 
to operate independently, i.e., one three-way switch must be wired at the 
AC source side of the system (sometimes called the "line" side), the other 
three-way switch must be wired at the load side of the system, and the 
four-way switch must be electrically situated between the two three-way 
switches. As another example, a four switch system requires two four-way 
switches and two three-way switches, wired in well known fashion, to 
render all switches fully operable to independently control the load. In 
this exemplary four switch system, the prior art requires one three-way 
switch to be wired at the line side of the system, the other three-way 
switch to be wired at the load side of the system, and the two four-way 
switches to be electrically situated between the two three-way switches. 
In the prior art four-way switch systems, the electrical location of the 
four-way switches is critical to maintain proper system operation; they 
must be electrically situated between the three-way switches, else system 
wiring changes may be necessary. 
Three-way dimmer switches can be used in four-way switch applications, but 
the dimmer switch must, when used in conjunction with standard three-way 
and four-way switches, be wired into one of the locations where the 
three-way switch would normally be placed, i.e., at either the line side 
or the load side of the system. In the prior art, faulty operation of the 
switching system results if the dimmer switch is wired at one of the 
(intermediate) four-way switch locations. Another drawback is that the 
power level delivered to the load (dimming level) can only be adjusted at 
the location where the dimmer is situated. 
Three-way and four-way dimming systems that employ a dimmer switch and one 
or more specially designed auxiliary (remote) switches that permit the 
dimming level to be adjusted from multiple locations have been developed, 
but they suffer from the same drawback as described above, i.e., the 
dimmer switch must be wired at either the line or load side of the system. 
Moreover, the pair of wires of the dimmer switch that are used to connect 
it to system wiring (and that also carry the load current--sometimes 
called the "hot" and "dimmed hot" lead wires), must be properly connected 
to the system wiring (i.e., with the hot lead wire connected to the line 
side of the system and the dimmed hot lead wire connected to the load side 
of the system); if the wiring of these wires is reversed, the dimming 
system may not operate properly. 
Commonly assigned U.S. Pat. No. 5,248,919 (the 919 patent), incorporated 
herein by reference in its entirety, discloses a multiple location 
lighting control system, including a wall mountable dimmer switch and wall 
mountable remote switches for wiring at all (N) locations of a multiple 
location switch system. The dimmer switch and the remote switches, all of 
which are subjected to AC source voltage and carry full load current, each 
have intensity raise, intensity lower and toggle load on/off actuators, 
and the dimmer switch is responsive to actuation of any of these actuators 
to alter the dimming level (or power the load on/off) accordingly. In 
particular, actuation of an actuator at any of the remote switches causes 
an AC control signal or partially rectified AC control signal (having 
source voltage) to be communicated from that remote switch to the dimmer 
switch over one of the wires of the AC wiring interconnecting the various 
switch locations, and the dimmer switch is responsive to receipt of the 
control signal to alter the dimming level or toggle the load on/off. Thus, 
the load can be fully controlled from any of the N locations. A drawback 
of the system disclosed in the 919 patent is that the dimmer switch must 
be wired at the line side or load side of the switch system. Stated 
otherwise, if the switch location wired to the line side of the system is 
defined as the first switch location, and the switch location wired to the 
load side of the system is defined as the last, or Nth, switch location, 
then the dimmer switch cannot be wired at a switch location electrically 
intermediate the first and last switch locations. 
The dimmer switch of the 919 patent employs a triac to control the dimming 
level, and a microprocessor controls the firing angle of the triac via the 
gate terminal. Each main terminal of the triac is coupled to a hookup wire 
of the dimmer switch, one through a choke (not shown); one hookup wire 
defines the hot lead of dimmer switch and the other hookup wire defines 
the dimmed hot lead of the dimmer switch. Thus, these two hookup wires are 
subjected to source voltage and carry full load current during system 
operation. The dimmer switch also has a third hookup wire, a control wire, 
that interconnects all of the switches in the system, and that carries the 
above mentioned control signals to the dimmer switch. The control wire 
does not carry full load current, but as mentioned, the signals are of the 
same voltage as the AC source. A conventional four-way wiring scheme may 
be employed to interconnect various switch locations, i.e., they may be 
interconnected by three conductor wire, such as type NM 14/3 or 12/3 
wiring. Thus, the system of the 919 patent is particularly suited for use 
in an installation that has already been wired for a four-way switch 
system. However, one drawback of the dimmer switch of the 919 patent is 
that the dimmer switch will not respond to the actuation of the actuators 
on some, or possibly all, of the auxiliary switches if the hot and dimmed 
hot leads of the dimmer switch are reversed. 
A commercial embodiment of the dimming system disclosed in the 919 patent 
is presently manufactured by the assignee hereof, Lutron Electronics Co., 
Inc., Coopersburg, Pa. ("Lutron"), under the trademark MAESTRO.RTM.. The 
MAESTRO.RTM. dimmer switch and remote switches function as above 
described, and also as further described in the 919 patent. The 
MAESTRO.RTM. system and components are more fully described in the Lutron 
publications entitled "LUTRON.RTM. Wallbox Lighting Catalog" (P/N 
360-178); "Symphony Series.TM..--A New Standard for Lighting 
Controls--MAESTRO.RTM.--The Smart Dimmer . . . " (P/N 360-326); and 
"Introducing Lutron's Symphony Series.TM.--A new Standard for Lighting 
Controls--MAESTRO.RTM.--The Smart Dimmer" (P/N 360/324), all of which are 
incorporated herein by reference. The MAESTRO.RTM. dimmer switch suffers 
from the same drawbacks discussed above in connection with the 919 patent. 
Thus, for example, in the MAESTRO.RTM., where the hot lead wire of the 
dimmer switch is a black wire, and the dimmed hot lead wire of the dimmer 
switch is a red wire, the dimmer switch will not respond to actuation of 
the actuators on the remote switches if the wiring of the black and red 
lead wires to the AC wiring is reversed. In the MAESTRO.RTM. dimmer 
switch, the third hookup wire, i.e., the control wire, is blue. 
Commonly assigned U.S. patent application Ser. No. 08/614,712 filed Mar. 
13, 1996 entitled "Lighting Control with Wireless Remote Control and 
Programmability" (the 712 application) incorporated herein by reference in 
its entirety discloses a dimmer switch similar in many respects to the 
MAESTRO.RTM. dimmer switch, but with the added feature of wireless remote 
control capability. According to the 712 application, an infra-red 
receiver is disposed within the dimmer switch and is responsive to 
infra-red commands from a handheld infra-red transmitter to adjust the 
dimming level. A commercial embodiment of such a dimmer switch is 
presently available from Lutron under the trademark SER.TM., and is 
more fully described in the Lutron publications entitled "SER.TM. 
Personal Space Light Control" (P/N 360-487), "Introducing SER.TM. 
Personal Space Light Control" ((P/N 362-899) and "SER.TM. Personal 
Space Light Control" (P/N 360-486), all of which are incorporated herein 
by reference. The SER.TM. dimmer switch also supports hard-wired remote 
switches that can be used to control the dimming level in much the same 
manner as the MAESTRO.RTM. dimmer switch. The SER.RTM. dimmer switch 
suffers from the same drawbacks as above described in connection with the 
919 patent and the MAESTRO.RTM. dimmer switch. 
The above described dimmer switches and their respective remote switches do 
not require connection to the neutral line of the AC source for their 
operation. But some dimmer switches that use controllable conductive 
devices (such as a triac) to control electronic loads do require a 
connection to the neutral line. Additionally, a neutral wire may be 
necessary when using a dimmer switch with a power supply in order to allow 
small loads (e.g., 25 watts) to be controlled. In a building with 
electronic loads and three-way and four-way switches that is being 
retrofitted with new controls that include a dimmer switch, it is possible 
that the neutral line is only located in one of the particular wall boxes. 
If this particular wallbox happens to be electrically situated between the 
wallbox wired to the line side and the wallbox wired to the load side, 
none of the above described dimmers can be used for the reasons previously 
explained, at least not without expensive rewiring. 
The ONSET.RTM. dimmer switch from Lightolier Controls, 2413 South Shiloh 
Road, Garland, Tex. 75041, and its associated remote devices use only two 
switches on the dimmer switch or the remote devices to perform multiple 
location dimming and on/off control. This dimmer switch is location 
dependent, i.e., it is incapable of being wired into a wall box wired for 
a four way switch. It also is wiring arrangement dependent, and the load 
current carrying wires cannot be interchangeably wired to the AC wiring. 
Systems of this type, modified as described herein, are considered to be 
within the scope of the instant invention. 
So-called "cycle" or "touch" dimmer switches, such as those manufactured by 
Leviton Manufacturing Co., Inc., 59-25 Little Neck Parkway, Little Neck, 
N.Y. 11362, and others, can be used in a multiple location switching 
system, but are also location dependent and wiring arrangement dependent. 
This type of dimmer switch has a plate that, when quickly touched, toggles 
the load, and when touched continuously, cycles the dimming level up and 
down until the touch is removed. 
It is desirable to provide a dimmer switch and switch system that overcomes 
the above shortcomings, and in particular, wherein the dimmer switch is 
location independent and wiring polarity independent. The present 
invention achieves these goals. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a wall mountable 
dimmer switch for controlling the level of AC power delivered from an AC 
source to a load, such as a lighting load. The dimmer switch of the 
present invention is particularly adapted for use in a multiple location 
switch system having at least three switch locations (i.e., a four-way 
switch system) although the present dimmer switch may be employed in 
three-way applications and as a stand alone (i.e., single pole) switch. 
The dimmer switch of the present invention may be wired into any one of 
the multiple switch locations, without regard to the arrangement of the 
wiring of the hot and dimmed hot lead wires of the dimmer switch to the AC 
system wiring. 
A dimmer switch according to the present invention comprises an electronic 
dimming circuit, preferably including a microprocessor that, in response 
to input data, provides an output signal that controls the firing angle of 
a triac in the dimming circuit. When employed in a multiple location 
switch system, the switch system preferably includes at least one remote 
device that, in response to actuation of intensity raise, intensity lower 
and toggle on/off switches disposed on the remote device, provide control 
signals over the AC system wiring to the dimmer switch. An auxiliary 
circuit is provided with signal and location detection circuitry. This 
circuit provides signals to the microprocessor; the microprocessor also 
receives signals from the zero crossing detector that indicate the 
polarity of the present half cycle of the AC source. The microprocessor 
determines, based upon these signals, whether to increase or decrease the 
power level to the load, or whether to toggle the on/off. As a result, the 
dimmer switch can be wired into any one of the locations of a multiple 
location switch system, without regard to the wiring of the hot and dimmed 
hot lead wires to the AC system wiring, while remaining responsive to the 
control signals from all of the remote switches in the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention is described herein as an improvement to the dimmer 
switch disclosed in the 919 patent, and more particularly, as an 
improvement to the MAESTRO.RTM. commercial embodiment thereof, but it 
should be understood that this is merely one preferred embodiment of 
carrying out the invention. The present invention is not limited to this 
particular disclosure, or to application in these particular types of 
dimmer switches, except as expressly set forth in the following claims. 
The present invention has applicability to any electronic dimmer switch, 
and to any multiple location dimming system. The present invention is 
described herein for use in controlling AC loads, but has particular 
application to controlling lighting loads. 
Referring now to the drawings, wherein like numerals and letters represent 
like elements, the following labeling conventions are used in the FIGS. 
B=black wire 
R=red wire 
BL=blue wire 
WH=white wire 
AC=alternating current source (typically 120 volts RMS) 
H=line side of the switch system, or hot lead wire of a switch, as 
appropriate 
Ne=neutral (AC source) wire 
WC=wire connector 
S=switch 
DS=dimmer switch 
LD=load 
l=lower switch 
r=raise switch 
t=toggle switch 
Turning now to FIG. 1, there is shown a system wiring diagram for a 
multiple location switching system, having N locations, 1 through N, each 
wired to receive a switch S. Each location N is preferably defined by a 
NEMA standard 3" high by 131/32" wide wall box, and each switch S.sub.1 
through S.sub.N is adapted to be received therein and wired to AC wiring 
present therein, as more fully described below. If the switching system 
employed is the above described MAESTRO.RTM. switching system, then the 
dimmer switch may be wired only at locations 1 or N, and not intermediate 
thereto, and the remaining switches S may be the above described remote 
switches (see the 919 patent for further details). Thus, if the dimmer 
switch is the switch S.sub.1 wired at location 1, then the remaining 
switches S.sub.2 through S.sub.N wired at locations 2 through N are the 
remote switches, and the dimmer switch S.sub.1 must be wired as shown, 
i.e., the black wire B.sub.1 of switch S.sub.1 (i.e., the hot lead wire of 
S.sub.1) must be wired to the line H and the red wire R.sub.1 (i.e., the 
dimmed hot lead wire of S.sub.1) should be wired to the black wire B.sub.2 
of the remote switch S.sub.2, etc., as shown. The system will still 
function if the arrangement of any of the red R and black B wires of any 
of the remote switches is reversed, e.g., if the red wire R.sub.2 of 
remote switch S.sub.2 is wired to the red wire R.sub.1 of the dimmer 
switch S1. As also shown, each of the switches S is interconnected by a 
control wire BL, which, as mentioned, is the blue wire of the prior art 
MAESTRO.RTM. switches. Each of the B, R and BL wires, the source (AC) and 
the load (LD) is shown as being interconnected by means of system wiring 
and wire connectors WC. It will be appreciated that the B and R wires 
(defining, for purposes of this application, first and second hookup 
wires) are subjected to source voltage and carry the full current drawn by 
the load LD; the BL wires are subjected to source voltage and carry low 
current, as their function is merely to communicate signals to the dimmer 
switch. As shown, the neutral wire (Ne), which is usually the white wire 
(WH) in an installation wired according to the National Electrical Code, 
does not need to be wired to any of switches S, and therefore the WH wire 
need not be, but can be, carried through any of the locations 1 through N. 
Thus, for purposes of this application, the term "AC wiring", when used to 
describe the wiring interconnecting the locations 1 through N means at 
least the wires interconnecting the locations 1 through N needed to 
connect the B and R wires of the switches S, and the term may include (but 
for purposes of the appended claims, does not necessarily include, except 
as specified therein or as may be implicit therein) the wires 
interconnecting the locations 1 through N needed to connect the BL wires 
of the switches S, as well as the wires connecting location 1 to the 
source and location N to the load. 
According to the present invention, the dimmer switch may be wired into any 
of the locations 1 through N, and the wiring of the B and R wires thereof 
wires may be reversed, and the system will operate properly. In other 
words, the dimmer switch of the present invention is location independent 
and wiring arrangement independent. 
In FIG. 2, the AC wiring 200 interconnecting the locations 1 through N is 
shown as having three wires. Preferably, the wiring 200 is three conductor 
wire, such as type NM 14/3 or 12/3 wiring. Two conductor wire, such as 
type NM 14/2 or 12/2, is preferably employed to interconnect location 1 to 
the source (wire 202), and to interconnect location N to the load (wire 
204). In the illustrated wiring diagram of FIG. 2, the neutral Ne is shown 
as being carried through each of the locations 1-N, but, as mentioned 
above, this is not necessary, and other wiring schemes are permissible. 
FIG. 2 illustrates the feature of the present invention that, irrespective 
of which of the locations 1 through N the dimmer switch of the present 
invention is wired, the wiring of the B or R wires to the AC wiring is 
independent; this is illustrated by the use of parenthesis at each 
location, e.g., B.sub.N (R.sub.N). It will be seen that the AC wiring 200 
also interconnects the BL wires, which are wired as shown in FIG. 1 to 
carry the control signals to the dimmer switch. In the example of FIG. 2, 
the dimmer switch may be any one of the switches S.sub.1 -S.sub.N. It will 
be appreciated that the particular wires of wiring 200 that interconnect 
the B and R wires of the switches S.sub.1 through S.sub.N define an AC 
load current carrying line, and that, when the B and R wires are connected 
thereto, they define a portion of the AC load current carrying line. 
FIG. 3 illustrates, in block diagram form, a dimmer switch 10 according to 
the present invention. As mentioned, dimmer switch 10 hereof may be the 
same dimmer switch 10 described in the 919 patent, and the MAESTRO.RTM. 
commercial implementation thereof, modified as described herein. Elements 
20, 22, 24, 26, 28, 29, 30, 34, 36, 36', 38 and 38' (and, except as noted, 
the interconnections) of FIG. 3 hereof are identical to those of FIG. 2 of 
the 919 patent, and therefore the 919 patent's description of its dimmer 
switch 10 is applicable to FIG. 3 hereof. Accordingly, a detailed 
description of FIG. 3 hereof is not required here, and reference is made 
to the 919 patent therefor. It will suffice to say that signal and 
location detector 33 serves the function of receiving signals from local 
switches "t", "r" and "I" and remote switches labeled "REM" in FIG. 3, and 
providing the same to microprocessor 28, which is responsive thereto to 
increase or decrease the dimming level, or to toggle the load on/off. In 
particular, when the actuator for the "I" switch is actuated at one of the 
local switches (or the auxiliary switches REM), diode 38 (38') permits 
only half cycles of one polarity of the source voltage to be communicated 
over the AC wiring interconnecting the BL wires to the signal and location 
detector 33. Similarly, actuation of the actuator for the "r" switch 
(together with operation of diode 36, 36') permits communication of only 
half cycles of the other polarity. Actuation of the actuator for the "t" 
switch (which has no associated diode) permits communication of full 
cycles. Each of these signals, which is either full AC (actuation of "t" 
switch) or rectified AC (actuation of "I" or "r" switches), and which has 
the magnitude of the AC source, is converted to logic levels by signal and 
location detector 33 suitable for input to microprocessor 28. 
Microprocessor 28 is programmed to be responsive thereto, and to an input 
from a zero crossing detector 30, to raise or lower the dimming level or 
to toggle the load on/off. Each actuator for the "I" and "r" switches is a 
user operable actuator, preferably in the form of a rocker actuator or the 
like, and the actuator for the "t" switch is preferably in the form of a 
push button actuator, as in the MAESTRO.RTM. dimmer switch. 
In certain embodiments, it may be desirable to design the dimmer switch 10 
so that the power supply 34 thereof (and other circuit elements, if 
desired) receive and utilize the neutral line of the system wiring. This 
is shown by the dashed line Ne' in FIG. 3. 
In FIG. 3, the designations B, R and BL have been provided to designate the 
wires previously discussed. According to the present invention, the 
circuitry (FIG. 2) of the 919 patent is modified in that a location 
detector has been added, and interconnections 37 and 35 to the hot (B) and 
dimmed hot (R) sides of triac 22 are provided to the signal and location 
detector 33, as shown. Signal location detector 33 defines "auxiliary 
circuitry". A connection 41 between the control wire BL and signal and 
location detector 33 is also provided. Signal and location detector 33 
provides inputs to microprocessor 28 on line 39 and line 43. Programming 
of microprocessor 28 is also modified as described hereinafter. As 
explained hereinafter, signal and location detector 33 provide inputs to 
the microprocessor 28 for processing, along with inputs from the zero 
crossing detector 30. This is described in further detail hereinafter. 
This feature of the present invention not only permits the dimmer switch 
to be wired into any of the locations 1 through N while preserving the 
operation of all of the auxiliary switches, it also permits the hot (B) 
and dimmed hot (R) lead wires of the dimmer switch to be interchangeably 
wired to the AC wiring. 
FIG. 4 illustrates further features and details of the present invention. 
In FIG. 4, the dimmer switch 10 is shown as being wired in location 2, 
i.e., electrically situated between the remote switches wired in locations 
1 and 3 through N. The remote switch on the source side of dimmer switch 
10 is labeled REM S, and the remote switch on the load side of dimmer 
switch 10 is labeled REM L. Each remote switch comprises "I", "r" and "t" 
switches, and diodes 36', 38', as above described, and as further 
described in the 919 patent. However, in accordance with yet another 
aspect of the invention, each remote switch may be provided with an 
infrared (IR) or radio frequency (RF) receiver 12 adapted to receive 
commands from a hand held IR or RF remote transmitter having similar "I", 
"r" and "t" switches thereon that provides, in response to actuation 
thereof, IR or RF signals indicative of desired lower, raise and toggle 
on/off conditions. The IR/RF receiver 12 is responsive to receipt of such 
signals to provide the same AC signals (negative half cycle only, positive 
half cycle only, or full cycle) on the control wire BL as are provided 
when any of the hard-wired switches "I", "r" and "t" on the remote 
switches are actuated. The IR/RF receivers 12 may be provided in addition 
to the hard-wired switches, or, may be implemented as part of a remote 
unit that is only a receiver having no local controls. Moreover, an IR/RF 
receiver may be provided in the dimming switch 10 (not shown), if desired. 
It will be appreciated from both FIGS. 3 and 4 that the dimmer switch 10 
is preferably provided with local "I", "r" and "t" switches for carrying 
out dimming level and toggle on/off functions locally at the dimmer 
switch. It should also be noted that the B(R) convention has been employed 
to indicate that the wiring of the B and R hookup wires is reversible. 
Implementation of the IR/RF transmitter and receiver functions will be 
readily apparent to those skilled in the art, and therefore details 
thereof are not provided herein. For example, the above referenced 712 
application, and the above referenced SER.TM. lighting control unit, 
teach such an implementation. U.S. Pat. Nos. 5,005,211; 5,099,193; 
5,146,153; and, 5,237,264, each of which is incorporated herein by 
reference, also teach implementation of an IR remote control system. 
FIG. 4 illustrates each of the remote switches REM as having two 
conductors, labeled B and R, both of which are subject to source voltage 
and carry full load current during system operation. In the above 
mentioned MAESTRO.TM. commercial implementation, the remote switches are 
provided with mechanical, user operable, air gap switches not shown, and 
the B and R wires are coupled to opposite sides of the air gap switch. 
Those skilled in the art will readily appreciate that only one conductor 
for connection to the system wiring is required if the air gap switch is 
not employed. Thus, it is possible to provide a remote switch having only 
two lead wires, i.e., a control wire (BL) and a wire for connection to the 
system wiring and, in operation, both of which are subject to source 
voltage but do not carry full load current. A system employing such a 
switch is within the scope of this invention. 
Turning now to FIG. 5, circuitry for implementing block 33 of FIG. 3 is 
illustrated. Essentially, the signal and location detector 33 comprises 
optical isolators 16, 14 and voltage divider (R1, R2, R3) circuitry for 
providing a pair of logic outputs OPT1 and OPT2 that change state 
depending upon the nature of the command ("I", "r" or "t"), its direction 
of origin relative to the dimmer switch, and, in some cases, the present 
half cycle (positive or negative) of the waveform of the AC source. 
Generally speaking, opto-isolator 14, resistor R3, and capacitor C1 and 
opto-isolator 16, resistor R4 and capacitor C2 define signal and location 
detector 33. Since OPT1 and OPT2 may, in some cases, change state with 
changes in the polarity of the AC source waveform from positive to 
negative, and negative to positive, the microprocessor 28 must be provided 
with input indicative of when such changes in the AC source waveform occur 
so that it can properly interpret the OPT1 and OPT2 inputs. That is the 
function of zero crossing detector 30 in FIG. 3. In one preferred 
embodiment of the invention, the values of the components R1-R6, C1 and C2 
are as follows: 
______________________________________ 
R1, R2 33 Kohm 
R3 4.7 Kohm 
R4 1 Kohm 
R5, R6 7.5 Kohm 
C1, C2 0.1 uF 
Opto isolators Toshiba P/N TLP-620-D4-6B 
14, 16 
______________________________________ 
Though the disclosed circuitry employs optical isolators for isolating the 
AC side from the low voltage digital side, those skilled in the art will 
readily appreciate that other isolation devices, such as transformers, may 
be employed, and that a dimmer switch without any isolation devices may be 
provided. Both of these alternatives are considered to be within the scope 
of the present invention. 
The operation of the circuitry of FIG. 5 is best illustrated by reference 
to both FIGS. 4 and 5, and by discussion of the current paths for various 
actuations of the switches "I", "r" and "t" of the remote switches REM S 
and REM L. In the following discussion, the current path is described in 
relation to the circuit components of FIG. 5; references to B, R and BL 
are to the wires labeled B, R and BL in FIG. 5. 
1) Actuation of "t" on REM S 
During all half cycles, the main current path is the same, since there is 
no diode in the current path when "t" on REM S is closed. The main current 
path is defined by BL, R4, R2 and R. Some of the current also flows 
through opto-isolator 16. Opto-isolator 16 is therefore "on", and OPT1 is 
low (L) (essentially ground), for all half cycles during which "t" is 
closed. No current flows through R3, and therefore opto-isolator 14 is 
"off" and OPT2 is high (H) (+5 v) for all half cycles during which "t" is 
closed. 
2) Actuation of "t" on REM L 
During all half cycles, the main current path is the same, since there is 
no diode in the current path when "t" on REM L is closed. The current path 
is defined by BL, R4, R3, R1 and B. Some of the current also flows through 
opto-isolators 14 and 16. Opto-isolators 14 and 16 are therefore both 
"on", and both OPT1 and OPT2 are low for all half cycles during which "t" 
is closed. 
Hereafter, it will be appreciated that whenever current flows through R3, 
some current will also flow through opto-isolator 14; and that, whenever 
current flows through R4, some current will also flow through 
opto-isolator 16. 
3) Actuation of "r" on REM S 
When "r" on REM S is closed, diode 36' of REM S conducts during positive 
half cycles. During positive half cycles, the current path is defined by 
BL, R4, R2 and R, and no current flows through R1 or R3; during this time 
opto-isolator 16 is "on" and opto-isolator 14 is "off", and thus OPT1 is 
low and OPT2 is high. During negative half cycles, the current path is 
defined by R, R2, R3, R1 and B; during this time, opto-isolator 16 is 
"off" and opto-isolator 14 is "on", and thus OPT1 is high and OPT2 is low. 
4) Actuation of "r" on REM L 
When "r" on REM L is closed, diode 36' of REM L conducts during negative 
half cycles. During negative half cycles, the current path is defined by 
B, R1, R3, R4 and BL, and no current flows through R2; during this time 
both opto-isolators 14 and 16 are "on", and thus OPT1 and OPT2 are low. 
During positive half cycles, the current path is defined by B, R1, R3, R2, 
and R; during this time, opto-isolator 16 is "off" and opto-isolator 14 is 
"on", and thus OPT1 is high and OPT2 is low. 
5) Actuation of "I" on REM S 
When "I" on REM S is closed, diode 38' on REM S conducts during negative 
half cycles. During negative half cycles, the current path is defined by 
BL, R4, R2 and R, and no current flows through R1 and R3; during this 
time, opto-isolator 16 is "on" and opto-isolator 14 is "off", and thus 
OPT1 is low and OPT2 is high. During positive half cycles, the current 
path is defined by B, R1, R3, R2 and R; during this time, opto-isolator 14 
is "on" and opto-isolator 16 is "off", and thus OPT1 is high and OPT2 is 
low. 
6) Actuation of "I" on REM L 
When "I" on REM L is closed, diode 38' on REM L conducts during positive 
half cycles. During positive half cycles, the current path is defined by 
B, R1, R3, R4 and BL and no current flows through R2; during this time, 
both opto-isolators 14 and 16 are "on", and thus OPT1 and OPT2 are low. 
During negative half cycles, the current path is defined by B, R1, R3, R2 
and R; during this time, opto-isolator 14 is "on" and opto-isolator 16 is 
"off", and thus OPT1 is high and OPT2 is low. 
7) No Actuation 
When no actuator is actuated, the current path is the same for both half 
cycles. The current path is B, R1, R3, R2 and R, and opto-isolator 14 is 
"on" and opto-isolator 16 is "off", and thus OPT 1 is high and OPT2 is low 
for both half cycles. 
The above operation is summarized in FIG. 6. Microprocessor 28 may be 
programmed with a look-up chart similar to that of FIG. 6 to process the 
OPT1, OPT2 and zero crossing inputs, and provide the appropriate 
raise/lower or toggle on/off drive signals to gate drive circuitry 26 and 
triac 22. 
Prior art dimmer switches cannot detect the direction of origin of the 
control signals from the remote switches, and this is one reason that 
prior art dimmer switches are incapable of being wired electrically 
intermediate the auxiliary switches. In the present invention, 
microprocessor 28 interprets the OPT1 and OPT2 signals along with the zero 
cross detector signals and carries out the correct dimming function. 
FIGS. 7 and 8 illustrate an alternative embodiment of the invention 
wherein, instead of a single control wire BL, the dimmer switch employs a 
pair of control wires BL and BL/WH (BL in the embodiment illustrated) over 
which control signals are communicated by the remote switches. In the 
embodiment of FIG. 7, remote switches wired on the line side of the dimmer 
switch DS have their control wire BL wired to one of the BL or BL/WH 
(BL/WH in the embodiment illustrated) control wires of the dimmer switch, 
and the remote switches wired on the load side of dimmer switch have their 
control wire BL wired to the other one of BL or BL/WH control wires of the 
dimmer switch. FIG. 8 illustrates circuitry for generating the signals 
OPT1 and OPT2 in this alternative embodiment. Circuit components in FIG. 8 
have been labeled with like designations as in FIG. 5 to indicate like 
component values as set forth above with the exception of R3, which is 1 
Kohm in this embodiment. FIG. 9 is a chart illustrating the outputs of 
OPT1 and OPT2 of FIG. 8 for various conditions of the "r", "I" and "t" 
switches at positive and negative cycles of the AC waveform, and for the 
"r", "I" and "t" switches on remote switches connected on both the line 
and the load side of the dimmer switch. 
The operation of the circuit of FIG. 8 will be readily apparent to one 
skilled in the art after having read and understood the above description 
of the operation of FIG. 5. By way of example, the operation of the "r" 
actuator on REM S and of the "I" acturator on REM L is as follows: 
1) Actuation of "r" on REM S 
When "r" on REM S is closed, diode 36' of REM S conducts during positive 
half cycles. During positive half cycles, the current path is defined by 
BL, R4, R2, R; during this time, opto-isolator 16 is "on" and thus OPT2 is 
low. During negative half cycles, there is no current path; during this 
time opto-isolator 16 is "off" and thus OPT2 is high. The status of the 
output from OPT1 is irrelevant. 
2) Actuation of "I" on REM L 
When "I" on REM L is closed, diode 38' of REM L conducts during positive 
half cycles. During positive half cycles, the current path is defined by 
B, R1, R3, BL/WH; during this time, opto-isolator 14 is "on" and thus OPT1 
is low. During negative half cycles, there is no current path; during this 
time, opto-isolator 14 is "off" and thus OPT1 is high. The status of the 
output from OPT2 is irrelevant. 
Though the present invention has been described for use in a multiple 
location switch system, it will be appreciated that the instant dimmer 
switch is capable of stand-alone use, as well as in three and four way 
applications. 
In either case, it is preferred that the dimmer switch and remote switches 
described above be wall mountable, preferably for mounting in a NEMA 
standard 3" high by 131/32" wide wall box 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof, and 
accordingly, reference should be made to the appended claims, rather than 
to the foregoing specification, as indicating the scope of the invention.