Method and apparatus for remotely controlling an electrical appliance

A transmitter (12) has an output (13) adapted to be connected across an alternating current power line (AC1, AC2) at a point remote from an appliance (24) to be controlled. The transmitter generates one pulse per cycle of the alternating current. The pulse phase has a predetermined value with respect to the alternating current. A receiver (21) is adapted to be connected across the power line to couple the line to the appliance. When the receiver detects transmitter generated pulses during phase windows occurring each alternating current cycle, power is applied from the line to the appliance for the remainder of such alternating current cycle. The transmitter has an adjustment (14) that permits the phase of the transmitter generated pulses to be modulated and the receiver has an adjustment (26) that permits the position of the phase windows relative to the alternating current to be changed. The transmitter generated pulses and the phase windows occur only on every other half cycle of the alternating current. The transmitter includes a controlled rectifier which is fired on every other half cycle of the alternating current to generate the transmitter pulses; after firing, the controlled rectifier remains in a conducting state during the remainder of the alternating current half cycle.

BACKGROUND OF THE INVENTION 
This invention relates to electrical power control and, more particularly, 
to a method and apparatus for remotely controlling an electrical appliance 
connected across an electrical power line. 
It is often desirable to remotely control an appliance connected to an 
electrical outlet. If the plan for such remote control is known before the 
electrical wiring is installed, wall switches can be provided at the 
appropriate locations to control application of electrical power to the 
outlets to which the appliances are to be connected. If the user of the 
building wishes to establish a plan for remote control of appliances after 
the electrical wiring is in place, there are known techniques for 
signalling a switch at the appliance over the existing electrical wiring 
to turn the appliance on and off. 
One such technique described in Durkee U.S. Pat. No. 3,689,886 transmits 
one of a plurality of high frequency tone signals over power lines to 
control an electrical appliance; each frequency represents a separate 
control channel. A filter is provided for each remote switch to select the 
frequency corresponding to the particular channel. The filtered tone 
signal received at a remote switch is rectified and integrated to produce 
a switch actuating signal. Durkee uses time division multiplexing to 
increase the effective number of channels. The total number of channels is 
the product of the number of different frequency tone signals and the 
number of time slot divisions. In addition to the likelihood that high 
frequency tone signals will interfere with communication equipment such as 
radio and television connected to the power line, Durkee's technique has 
the shortcomings normally associated with high frequency equipment such as 
high cost, instability, and lack of reliability. 
Another technique disclosed in Woods U.S. Pat. No. 3,594,584 uses for 
signalling periodic pulses at a frequency several times higher than the 
line frequency and in no particular phase relationship to the alternating 
current. At the remote outlets, the pulses are rectified and integrated to 
produce a switch actuating signal. Woods only makes provision for one 
control channel, which severely limits the usefulness of his technique, 
and his switch is susceptible to accidental actuation by spurious signals 
and noise on the power line. 
SUMMARY OF THE INVENTION 
According to the invention, an electrical appliance connected across an 
alternating current power line is remotely controlled by pulses occurring 
at the frequency of the alternating current. A transmitter has an output 
adapted to be connected across an alternating current power line at a 
point remote from an appliance to be controlled. The transmitter generates 
one pulse per cycle of the alternating current. A characteristic of the 
transmitter generated pulses has a predetermined value. A receiver is 
adapted to be connected across the alternating current power line to 
couple the line to the appliance. Responsive to the transmitter generated 
pulses, the receiver transfers power from the line to the appliance as a 
function of the characteristic of the pulses. Preferably, the 
characteristic is the phase of the generated pulses relative to the 
alternating current on the line and the receiver applies power from the 
line to the appliance only when the phase of the transmitter generated 
pulses is the predetermined value. 
It is particularly advantageous to use phase as the pulse characteristic of 
the transmitter generated pulses because the transmitter and receiver can 
be synchronized by the zero crossings of the alternating current on the 
line. Specifically, a time delay circuit at the transmitter controls the 
generation of pulses so as to produce a pulse a predetermined time after 
every other zero crossing of the alternating current and another time 
delay circuit at the receiver controls the start of time slots during 
which the receiver can respond to pulses on the line so such time slots 
begin a predetermined time after every other zero crossing of the 
alternating current. The time slots embrace the transmitter generated 
pulses, thereby causing the receiver to be insensitive to noise and pulses 
outside the time slot. 
A feature of the invention is establishment of different signalling 
channels on the power line by modulating the pulse characteristic. 
Specifically, the pulse characteristic has a different predetermined value 
for each channel. When the pulse characteristic is phase, some of the 
transmitters and receivers connected across the power line can communicate 
with each other to the exclusion of other transmitters and receivers 
connected across the line by means of pulses occurring a predetermined 
time after alternate zero crossings of the alternating current. A 
particular transmitter or transmitters initiating the communication 
generate pulses having such time relationship to the alternating current 
and a particular receiver or receivers respond to pulses having such time 
relationship to the alternating current while the remaining receivers do 
not. 
Another feature of the invention is the provision of transmitters and 
receivers that generate and respond respectively to pulses during only 
one-half cycle of the alternating current. By switching the polarity of 
connection of the transmitters and receivers to the power line, the number 
of channels can be doubled, vis-a-vis, the number of predetermined values 
of the pulse characteristic. 
Another feature of the invention is the provision of a transmitter that 
generates a trigger pulse during every other half cycle of the alternating 
current and a receiver including first and second switches connected in 
parallel and coupling the line to the appliance. The first switch 
comprises a controlled rectifier having a gate electrode. The controlled 
rectifier fires to conduct unilaterally during the remainder of a half 
cycle of alternating current when a transmitter generated trigger pulse is 
applied to the gate electrode. The second switch is closed during half 
cycles of the alternating current immediately following application of 
each trigger pulse to the gating electrode. This arrangement permits a 
simple and reliable circuit implementation of a transmitter and receiver 
having all of the above enumerated features.

DETAILED DESCRIPTION 
In FIG. 1, electrical conductors AC1 and AC2 comprise an alternating 
current power line carrying for example 110-volt or 220-volt, 60-cycle 
electrical power. An electrical wall socket 10 and a power switch 11, such 
as for example a conventional manually operated wall switch, are connected 
in series across the line, i.e., between conductors AC1 and AC2. Switch 11 
has an open state and a closed state. A transmitter 12 is connected across 
the power line by a plug 13 inserted in socket 10. When switch 11 is 
closed, transmitter 12 receives power from the line and generates one 
pulse per cycle of the alternating current on the line, as described in 
more detail below in connection with FIG. 4. A characteristic of these 
pulses has a predetermined value. This characteristic is preferably the 
phase of the pulses relative to the alternating current on the line, but 
could be other characteristics such as for example pulse duration or 
amplitude. The predetermined value of the characteristic can be changed by 
an adjustment 14 such as for example a select switch or a potentiometer. 
By virtue of the connection through plug 13 and socket 10, the pulses 
generated by transmitter 12 are applied to the power line. 
At a point along the power line remote from socket 10, switch 11, and 
transmitter 12, a wall socket 20 is connected across the power line, i.e., 
between conductors AC1 and AC2. A receiver 21 is connected across the 
power line by a plug 22 inserted in socket 20. Receiver 21 has a socket 23 
connected in series with plug 22 through a normally open switching circuit 
described in more detail in connection with FIGS. 5 and 6. An electrical 
appliance 24 such as a lighting fixture, a television set, a coffee maker, 
or other device that consumes electrical power has a plug 25 that is 
inserted in socket 23 to connect appliance 24 across the line. The 
switching circuit of receiver 21 is actuated, i.e., closes, responsive to 
pulses on the line that have the characteristic, i.e., phase, with a 
predetermined value. The predetermined phase value to which receiver 21 
responds can be changed by an adjustment 26, which could be for example a 
select switch or a potentiometer. 
Conductors AC1 and AC2, socket 10, switch 11, and socket 20 are all part of 
a pre-existing power distribution system to which transmitter 12, receiver 
21, and appliance 24 are connected by inserting plug 13 in socket 10, plug 
22 in socket 20, and plug 25 in socket 23. Thus, appliance 24, which is 
connected in series with receiver 21 across the line at remote socket 20 
can be controlled by operating switch 11 after transmitter 12 is connected 
in series therewith across the line. A number of additional transmitters 
and receivers can also be connected across the line to effect remote 
control of additional appliances. Separate signalling channels for such 
remote control can be established by selecting different predetermined 
values of the characteristic, i.e., phase, for different pairs or 
combinations of transmitters and receivers. In other words, the 
transmitter generated pulses are modulated, i.e., phase modulated, to 
selectively control specific receivers. Any transmitter and receiver 
combinations that are to operate together, are set by adjustments 14 and 
26, respectively to the same predetermined value of the pulse 
characteristic, i.e., phase; the remaining receivers will not respond to 
pulses having this predetermined phase value and the remaining 
transmitters will not generate pulses having this predetermined phase 
value. 
Referring now to FIG. 2, curve A shows a wave form of alternating current 
on a power line, including pulses generated by transmitter 12 in every 
other positive half cycle of the alternating current. Curve B shows the 
wave form of the alternating current power applied to appliance 24 when 
the switching circuit in receiver 21 is actuated responsive to the 
transmitter generated pulses. It is assumed that prior to time T.sub.0, 
when the alternating current (AC) power is passing through its positive 
going zero crossing, no power is applied to appliance 24. At time T.sub.1, 
which lags the positive going zero crossing by a relatively small amount, 
e.g., 10.degree. or less, transmitter 12 generates a pulse and power is 
applied to appliance 24. As a result of the pulse at time T.sub.1, power 
is applied to appliance 24 during the remainder of this half cycle of the 
AC power, as well as all of the following half cycle. When the AC power 
passes through its positive going zero crossing at time T.sub.2, 
application of power to appliance 24 is terminated. At time T.sub.3, which 
lags the positive going zero crossing by the same amount as T.sub.1, 
another pulse is generated by transmitter 12 and power is reapplied to 
appliance 24 for the remainder of this half cycle and the following half 
cycle of AC power. If transmitter 12 is turned off by flipping switch 11 
after time T.sub.3, application of power to appliance 24 is terminated at 
the end of the following half cycle of AC power, designated time T.sub.4. 
Curves C and D show the wave form of alternating current on the power 
line, including the transmitter generated pulses, and the wave form of the 
power applied to appliance 24, respectively, when the polarity of the 
terminals of plug 13 in socket 10 and of plug 22 in socket 20 are 
reversed. In this case, the transmitter generated pulses occur in every 
other negative half cycle of the AC power and power is applied to 
appliance 24 in phase lagging relationship to the negative half cycles of 
AC power. 
Referring now to FIG. 3, which illustrates how separate signalling channels 
are established for different predetermined phase values of the 
transmitter generated pulses, curve A shows a single period of the AC 
power. In curves B through E, respectively, pulses T.sub.B, T.sub.C, 
T.sub.D, and T.sub.E, respectively, represent transmitter generated pulses 
having different predetermined phase values lagging progressively more the 
positive going zero crossing of the AC power at time T.sub.0. In curves F 
through I, respectively, pulses T.sub.F, T.sub.G, T.sub.H , and T.sub.I, 
respectively, represent transmitter generated pulses having different 
predetermined phase values lagging progressively more the negative going 
zero crossing of the AC power at time T.sub.0. For a particular setting of 
adjustment 14, transmitter 12 generates a pulse in each positive half 
cycle of the AC power, for example, pulse T.sub.B, or a pulse in each 
negative half cycle of AC power, e.g., pulse T.sub.F, depending upon the 
polarity of plug 13 relative to socket 10. In other words, this polarity 
sensitivity doubles the number of channels that can be established by 
phase modulating the transmitter generated pulses within every other half 
cycle of the AC power. The switching circuitry of each receiver is 
responsive only to transmitter generated pulses having a predetermined 
phase value or more properly, transmitter generated pulses occurring 
within a narrow phase, range, i.e., window, embracing the predetermined 
phase value of the transmitter generated pulses. The position of the phase 
window is set by adjustment 26. The phase windows that can be selected for 
receiver 21 are represented in curves J through M. As illustrated, the 
phase windows represented in curves J through M are synchronized with 
transmitter generated pulses T.sub.B through T.sub.E, respectively, i.e., 
they embrace such pulses. For operation of a particular combination of 
transmitters and receivers together, the transmitter of transmitters are 
adjusted to generate pulses having a predetermined phase value, e.g., 
pulse T.sub.D, of curve D, and the receiver or receivers are adjusted so 
their windows are aligned, i.e., synchronized with the transmitter 
generated pulses, e.g., curve L. In order to reposition the phase windows 
on the negative half cycles of AC power, it is only necessary to reverse 
the polarity of the terminals of plug 22 in socket 20. Of course, the 
polarity of a receiver in its socket must be the same as that of the 
transmitter to which it should respond. 
Turning now to FIG. 4, transmitter 12 of FIG. 1 is shown in detail. 
Transmitter 12 basically consists of a resonant circuit 31, a thyristor 
pulse generating circuit 32, and a time delay trigger circuit 33, which 
functions as an adjustable phase shifting network. Transmitter 12 is 
connected across the AC power line by terminals TR1 and TR2 of plug 13. 
Plug 13 comprises terminals TR1 and TR2. A resistor R6, an inductor L1, a 
capacitor C3, and a controlled rectifier SCR1 are connected in series 
between TR1 and TR2. A capacitor C4 is connected from the junction of 
resistor R6 and inductor L1 to TR2. The wiper arm of a select switch S1 is 
connected by a timing capacitor C1 to TR2. Switch S1 has stationary 
contacts connected respectively by timing resistors R1, R2, R3, and R4 to 
the junction of resistor R6 and inductor L1. A coupling diode D1 is 
connected in series with the parallel combination of a holding resistor R5 
and a coupling capacitor C2 between the wiper arm of switch S1 and the 
gate electrode of SCR1. A diode D2 and a voltage producing resistor R7 are 
connected in parallel between TR2 and the gate electrode of SCR1. A diode 
D3 is connected between the gate electrode of SCR1 and its anode. SCR1 is 
poled to transmit current from TR1 to TR2, D1 and D2 are poled to transmit 
current toward the gate electrode of SCR1, and D3 is poled to transmit 
current away from the gate electrode of SCR1. D2 and D3 are poled opposite 
to SCR1. The components in a typical embodiment of transmitter 10 are the 
following values and types: 
R1=1000 ohms 
D1,D2,D3=HEP R0170 
R2=3000 ohms 
C1=0.1 mf 
R3=4700 ohms 
C2=0.02 mf 
R4=10 K ohms 
C3=0.1 mf 
R5=33 K ohms 
C4=0.1 mf 
R6=47 ohms 
L1=125 mh 
R7=1000 ohms 
SCR1=HEP R1218 
Transmitter generated pulses are produced by the timed discharge of the 
resonant circuit 31 across the AC power line when switch 11 is closed. 
During the negative half cycle of AC power, i.e., TR1 is negative with 
respect to TR2, controlled rectifier SCR1 is back biased and diodes D2 and 
D3 are forward biased. Accordingly, capacitor C3 is positively charged by 
the AC power through conductive diodes D2 and D3. The positive charge just 
described is measured across C3, i.e., between terminals 1 and 2 of the 
circuit of FIG. 4. The charging of capacitor C3 continues until the AC 
power reaches its negative peak. Additionally, during the negative half 
cycle, the voltage at node 5 of the transmitter is at a negative value 
thereby back biasing diode D1 and isolating SCR1 from the time delay 
circuit 33. 
During the positive half cycle of the AC power, i.e., TR1 is positive with 
respect to TR2, node 5 commences to rise in voltage value towards the AC 
power at a rate determined by the time constant resulting from the 
capacitance of capacitor C1 and the resistance of a resistor selected from 
R1 through R4. The selection of a resistor R1 through R4 is by means of 
select switch S1, which comprises adjustment 14. The gate electrode of 
SCR1 is coupled to node 5 of transmitter 12 by a triggering circuit 
comprised of a series diode D1 and a network formed by the parallel 
connection of R5 and C2. SCR1 remains non-conductive as long as its gate 
electrode potential remains below its turn-on threshold voltage. At such 
time that the voltage at node 5 rises above the combined forward breakdown 
voltage of D1 and the turn-on threshold voltage of SCR1, SCR1 will be 
rendered conductive, i.e., it fires, thereby discharging resonant circuit 
31 onto the AC power line. When SCR1 is rendered conductive, node 1 is 
placed at essentially ground potential. Capacitor C3 which was charged 
during the previous negative half cycle of AC power, is thus directly 
connected across terminals TR1 and TR2 and discharges through inductor L1 
and resistor R6 into the powerline, thereby generating a pulse of the form 
shown in FIG. 8. Initially, the polarity of the pulse is negative, but 
inductor L1 causes the pulse polarity to swing positive after the initial 
negative excursion. 
The delay circuit time constant and thus the time at which the voltage at 
node 5 exceeds the forward breakdown voltage of diode D1 and the turn on 
voltage of SCR1 is determined by the resistance value selected by select 
switch S1. Thus, select switch S1 sets the predetermined phase value of 
the transmitter generated pulses by selecting one of resistors R1 to R4. 
If the resistors, when going from R1 to R4, having increasing resistance 
values, the time delay or phase lag from the positive going zero crossing 
of AC power at which conduction of SCR1 occurs will accordingly increase. 
The time at which SCR1 turns on (predetermined by means of the selectable 
time constant of the time delay circuit) is measured with reference to the 
positive going zero crossing of the AC power. This is because SCR1 is 
rendered non-conductive when the AC power changes from the positive half 
cycle and commences the negative half cycle. It should be noted, however, 
that operation of the circuit is not restricted to the superposing of 
pulses on the positive half cycles and that by suitable circuit 
rearrangement, the voltage pulses may be superposed on the negative half 
cycles of the AC power. Specifically, the connection of terminals TR1 and 
TR2 to the AC power line is reversed. 
As the voltage at node 5 reaches the forward breakdown potential of diode 
D1 current begins to flow through capacitor C2, diode D1 and resistor R7. 
This current increases rapidly to a value determined by the rate of change 
of the voltage at node 5. The result of this current passing through R7 is 
to produce a voltage at node 4 that tends to follow the voltage at node 5, 
reduced in amplitude by the forward voltage drop of diode D1. This voltage 
provides a stable triggering source for SCR1. A unique feature of the 
described SCR triggering circuitry is that it is relatively insensitive to 
gate electrode current variations that would otherwise cause variations in 
pulse timing, because C2 acts as a small impedance when current begins to 
flow through D1, thereby supplying large current to the gate electrode of 
SCR1. This current decreases as C2 charges, thereby limiting current flow 
at peak line voltage. Resistor R5 provides holding current, through D1 and 
D3, to maintain SCR1 in a conducting state until the end of the positive 
half cycle of the AC power as the circuit rings; during the subsequent 
negative half cycle R5 discharges capacitor C2 in preparation for the next 
pulse cycle. By keeping SCR1 conducting during the entire positive half 
cycle, the ringing, i.e., oscillations in C3 and L1 are permitted to decay 
sufficiently to prevent high frequency line interference. 
Resistor R6 limits the surge current through SCR1, and capacitor C4 
increases the voltage pulse width and reduces radio frequency interference 
(RFI) effects that may be generated due to the resonant circuit discharge. 
Once SCR1 is conductive, the gate electrode of SCR1 is coupled to ground 
through forward biased diode D3 and SCR1. Besides isolating the gate 
electrode during the negative half cycles of the AC power, D1 also serves 
to prevent a voltage buildup on capacitor C2 during the negative half 
cycles which would cause premature triggering, i.e., turning on of SCR1. 
Resistor R7 provides the gate to cathode impedance frequently specified 
for sensitive gate SCR's in order to prevent the SCR from turning itself 
on at high anode to cathode voltages. 
Referring now to FIG. 5, receiver 21 is shown in detail. The receiver 21 
basically consists of plug 22 that couples the receiver to the AC power 
line, socket 23 that couples the receiver to appliance 24, a controlled 
rectifier thyristor switching circuit 36 and a delay and enabling circuit 
37. The receiver 21 is coupled to the AC power line by terminals RC1 and 
RC2 of plug 22 and is coupled to appliance 24 by terminals RC3 and RC4 of 
socket 23. Switching circuit 36 is actuated, i.e., closed, by transmitter 
generated pulses that have the proper phase relationship relative to the 
AC power. Terminals RC3 and RC4, an inductor L10, and a controlled 
rectifier SCR10 are connected in series across terminals RC1 and RC2, 
SCR10 being poled to conduct current from RC1 to RC2. A controlled 
rectifier SCR12, inductor L10, and terminals RC3 and RC4 are also 
connected in series between RC1 and RC2, SCR12 being poled to conduct 
current from RC2 to RC1. Thus, SCR10 and SCR12 are connected back-to-back 
in parallel with each other and in series with terminals RC3 and RC4 
across RC1 and RC2. A resistor R19 is connected between RC3 and the gate 
electrode of SCR12. A resistor R20 and a capacitor C13 are each connected 
between the gate electrode of SCR12 and its cathode. The wiper arm of a 
window selecting switch S2 is connected by a window determining capacitor 
C10 to RC2. The stationary contacts of switch S2 are connected by window 
determining resistors R11, R12, R13, and R14, respectively, to RC3. A 
diode D10, a coupling diode D12, a coupling diode D13, and a capacitor C12 
are connected in series between the wiper arm of switch S2 and the gate 
electrode of SCR10. A resistor R16 is connected in parallel with diode 
D10. A resistor R15 and a capacitor C11 are connected in series between 
RC3 and the junction of D10 and D12. A Zener diode ZR1 is connected 
between RC2 and the junction of D12 and D13. A resistor R17 is connected 
between RC2 and the junction of D13 and capacitor C12. A resistor R18 is 
connected between the cathode of SCR10 and its gate electrode. D10 is 
poled to conduct current toward the wiper arm of switch S2, D12 and D13 
are poled to conduct current toward the gate electrode of SCR10, and ZR1 
is poled to break down when the junction of D12 and D13 is positive with 
respect to RC2. The components in a typical embodiment of receiver 21 are 
the following values and types: 
R.sub.11 =100 ohms 
C11=0.1 mf 
R.sub.12 =2200 ohms 
C12=0.01 mf 
R.sub.13 =4700 ohms 
C13=10 mf 
R.sub.14 =10 K ohms 
C14=0.01 mf 
R.sub.15 =1000 ohms 
L10=250 mh 
R.sub.16 =33 K ohms 
D10, D12, D13=HEP R0170 
R.sub.17 =33 K ohms 
ZR1=9.1 volts 
R.sub.18 =1000 ohms 
SCR10, SCR12=HEP R1218 
R.sub.19 =47 K ohms 
R.sub.20 =1000 ohms 
Briefly, the operation of the receiver is as follows. The receiver is 
enabled, i.e., capable of detecting transmitter generated pulses on the AC 
power line, in predetermined time slots or phase windows lagging the 
positive going zero crossings of the AC power in phase. The phase lag of 
the time slots is determined by the resistance-capacitance time constant 
of capacitor C10, and one of resistors R11 through R14 selected by 
selector switch S2, which comprises adjustment 26. If during the selected 
time slot a transmitter generated pulse appears on the AC power line, it 
will be coupled to the receiver at terminals RC1 and RC2, and transferred 
by means of a normally disabled pulse transmission path comprising 
resistor R15, capacitor C11, diodes D12 and D13, and capacitor C12 to the 
gate electrode of controlled rectifier SCR10. The pulse at the gate 
electrode of SCR10 renders it conductive, i.e., fires SCR10, thereby 
completing an electrical path between terminals RC4 and RC2. Completing 
the aforementioned electrical path couples appliance 24 to the AC power 
line. During the negative half cycles of the AC power following positive 
half cycles when SCR10 is conductive, SCR12 is rendered conductive, i.e., 
fires, and SCR 10 is non-conductive so that appliance 24 is connected to 
the AC power line for the entire AC power cycle period except for the 
initial phase lag before the time slot caused by the enabling circuit 37. 
As long as a transmitter generated pulse appears on the AC power line on 
alternate half cycles, i.e., every positive half cycle, and such pulse is 
detected by the receiver, the appliance remains coupled to the AC power 
line. 
More specifically, the operation of the receiver is as follows. The portion 
of the receiver, i.e., circuit 37 that is coupled to the gate electrode of 
SCR10, provides a selectable time slot or phase window during which the 
receiver is enabled to detect a transmitter generated pulse on the AC 
power line. All pulses are noise outside the window are rejected by the 
receiver. A phase shift network comprising one of the resistors R11 
through R14, selected by the select switch S2, and capacitor C10 provides 
a voltage at node 6 that lags the powerline voltage by a predetermined 
amount. This voltage serves to open and close the receiver phase window. 
As the powerline voltage passes through zero at the beginning of a 
positive half cycle, the voltage at node 6 is still negative; this 
voltage, coupled through R16, reverse biases D12 and disables the pulse 
transmission path to the gate electrode of SCR10. The receiver phase 
window is closed. A positive pulse coupled through R15 and C11 at this 
time will see a low impedance path through D10 and C10 and will not 
overcome the reverse bias on D12. 
As the powerline voltage increases further the voltage at node 6 passes 
through zero and becomes positive. This voltage, coupled through R16 to 
node 7, forward biases D12, enables the pulse transmission path, and opens 
the phase window. The voltage at node 8 will begin to rise at the same 
rate as the voltage at node 6. When the voltage at node 8 reaches the 
forward breakdown of diode D13 further voltage changes at node 8 will be 
influenced by the voltage divider formed by R16 and R17. The phase window 
closes when the voltage at node 8 reaches the zener voltage of ZR1. 
In FIG. 7, curves V.sub.6, V.sub.7, and V.sub.8 represent the voltages at 
nodes 6, 7, and 8, respectively, from just before the phase window opens 
till after it closes. The ordinate is voltage amplitude and the abscissa 
is time. In FIG. 7, A represents the forward breakdown voltage of D12, B 
represents the forward breakdown voltage of D13, C represents the reverse 
breakdown voltage of zener diode ZR1, and D represents the voltage 
amplitude of the pulses passed through the enabling circuit. Once the 
window is open, a pulse coupled through R15 and C11 will cause the voltage 
at node 8 to increase, but node 8 is limited in amplitude to either the 
voltage at node 6 (through the action of D10 and D12) or to the zener 
voltage of ZR1, whichever is lower. 
As shown in FIG. 7, the amplitude of the pulse passed through the enabling 
circuit will vary according to when the pulse occurs within the phase 
window. The amplitude will be zero at the boundaries of the window and 
will be maximum at the point at which the node 6 voltage equals the zener 
voltage of ZR1. 
When the voltage at node 8, coupled from node 6 via R16 and D12, reaches 
the zener voltage of ZR1, the phase window is closed and the pulse 
transmission path is disabled. A positive pulse occurring at this time 
will see a low impedance across ZR1 and will not develop significant 
voltage at node 8. The switching characteristics of diode D12 allow a 
strong negative pulse to drive the voltage at node 8 momentarily negative; 
diode D13 prevents this transient from coupling through C12 to the gate 
electrode of SCR10. 
Resistor R15 serves to form a voltage divider with C10 before the phase 
window opens and with ZR1 after it closes to increase the attenuation of 
pulses occurring outside the phase window. Capacitor C11 is selected to 
pass the pulses received from the transmitter, but to block the normal AC 
powerline voltage. 
Capacitor C12 couples the pulses passed through the enabling circuit, which 
consist of high frequency components, to the gate electrode of SCR10 to 
render it conductive, but blocks the low frequency components of the 
enabling voltage, i.e., the components generated by the line voltage. 
Resistor R18 provides the low impedance gate to cathode connection 
frequently specified for sensitive gate SCR's to prevent self-triggering 
at high anode voltages. Inductance L10 isolates the switching transients 
generated by SCR10 and SCR12 from the AC power distribution network to 
prevent propagation of radio frequency interference. 
When a transmitter generated pulse is detected and SCR10 is rendered 
conductive, the resulting voltage drop across RC3 and RC4 charges 
capacitor C13 through resistors R19 and R20 so the gate electrode of SCR12 
becomes positive. Capacitor C13 maintains this positive voltage on the 
gate electrode of SCR12 for a sufficient time after the following negative 
going zero crossing of the AC power so as to render SCR12 conductive. Thus 
appliance 24 will be energized for each entire negative half cycle of the 
AC power after SCR10 is rendered conductive. 
The time (referenced to the positive going zero crossings) at which the 
window opens, i.e., the time in which the receiver becomes enabled, is 
determined by the resistance of the one resistor R11 to R14 selected by 
select switch S1, and the capacitor C10. The duration of the enabled 
period is determined primarily by the reverse breakdown voltage of zener 
diode ZR1. Thus, a plurality of appliances coupled to the power line by 
respective receivers can be individually controlled by a single 
transmitter; the receivers are all adjusted to have a different time slot 
or window and the phase of the transmitter generated pulses is simply 
adjusted to lie within the window of the receiver connected to the 
selected appliance. The combination of transmitters and receivers 
operating together can be programmed by simply adjusting them to operate 
on the same channel. 
The window is positioned early enough in time so as to minimize the 
influence of noise generated on the power line by such devices as lamp 
dimmer switches and motor speed controls, preferably within 10.degree. 
after the AC power zero crossings. Typically, most lamp dimmer switches 
turn on long after the zero crossings of the AC power. Thus, setting of 
the windows soon after the zero crossings isolates the receiver from such 
noise appearing on the power line. 
Alternatively, the selectable resistance values that determine the time at 
which the transmitter generated pulses occur can be provided by means of a 
potentiometer so as to have continuous, rather than discrete, control over 
the pulse phase. Similarly, a potentiometer can be used in the receiver to 
provide continuous control of the placement of the phase window. 
An alternative embodiment of the circuit 36 of FIG. 5 is shown in FIG. 6. 
Circuitry that includes a relay coil 40 and associated relay contacts K1 
is used in lieu of SCR12. Relay coil 40, a diode D15, and SCR10 are 
connected in series between RC3 and RC2. A diode D14 is connected in 
parallel with coil 40. Relay contacts K1 connect RC2 to RC4. A resistor 
R21 and a capacitor C14 are connected in series from the junction of SCR10 
and D15 to RC2. D14 is poled opposite to SCR10 and D15 is poled in the 
same direction as SCR10. 
Upon detection of a transmitter generated pulse on the power line, SCR10 is 
rendered conductive, and the relay coil 40 is energized, thereby closing 
relay contacts K1, coupling the appliance 24 to the AC power line. 
During the negative half cycle diode D14 provides a current path for the 
relay coil energizing current, thereby assisting the relay contacts to 
remain closed and provide continuous application of power to the 
appliance. Diode D15, resistor R21 and capacitor C14 provide sufficient 
current in order to turn on SCR10 when a pulse is applied to its gate. 
While the basic principle of this invention has been herein illustrated 
along with the embodiments shown, it will be appreciated by those skilled 
in the art that variations in the disclosed arrangement, both as to its 
details and the organization of such details, may be made without 
departing from the spirit and scope thereof. Accordingly, it is intended 
that the foregoing disclosure and the showings made in the drawings will 
be considered only as illustrative of the principles of the invention, and 
not construed in a limiting sense. For example, instead of applying power 
to the appliance when transmitter generated pulses are applied to the 
power line, power could be applied in the absence of such pulses. Or, 
instead of controlling the power in on/off fashion, the power applied to 
the appliance could be controlled in an analog fashion depending on the 
modulation of the transmitter generated pulses, e.g., the larger the phase 
lag of such pulses, the greater the applied power. In any case, power is 
transferred from the line to the appliance as a function of the 
characteristic, preferably phase, of the transmitter generated pulses. 
Although it is preferable to generate pulses at the transmitter on 
alternate half cycles of the AC power to increase the number of channels, 
these pulses could be generated on each half cycle with appropriate 
modifications of the transmitter and receiver. As disclosed herein, the 
transmitter issues pulses whenever the AC power circuit to which it is 
connected is energized. The transmitter could, however, incorporate a 
switch for manual operation, or incorporate means for responding to 
temperature, light, or another external stimulus.