Display for a remote receiver in an electrical utility load management system

A method and apparatus for monitoring and testing the operation and configuration of a remote receiver in an electrical load management system. The receivers are responsive to encoded command signals to remove electrical loads from the electrical distribution system. Upon receipt of a predetermined status inquiry command signal, the receiver retrieves status information pertaining to the receiver, and transmits the status information over a data communications link to a hand-held operator display unit. The operator display unit employs a short-range FM transmitter to transmit the predetermined status inquiry command signal, receives the transmitted status information, and displays the received status information to the operator on a display.

TECHNICAL FIELD 
The present invention relates generally to electrical utility load 
management systems, and more particularly it relates to an improved status 
display for a remote receiver for controlling an electrical load in an 
electrical load management system. 
BACKGROUND 
Electrical load management systems for allowing an electrical utility to 
control the load on the electrical system are known in the art. These 
systems operate to divert energy requirements to minimize electrical 
blackouts or "brown-outs". For example, U.S. Pat. No. 4,190,800 to Kelly, 
Jr., et al., entitled "Electrical Load Management System", assigned to the 
same assignee as the present invention, discloses an electrical load 
management system wherein a central station monitors the use of electrical 
power, and when peak demand periods occur, transmits coded information by 
radio from a central station to remote receivers mounted proximate the 
electrical loads. In this patent, the transmitted signal includes address 
and command information which is decoded at the receivers. Receivers which 
have been addressed pass command information over the distribution lines 
to the electrical loads, and thereby controls the operation of the 
customers' power consuming devices. 
Other load management systems employ separate radio receivers at each 
customer's location, rather than providing a receiver at the distribution 
transformer as in the aforementioned U.S. patent. Examples of this type 
system include the types DCU-1120, -1170, -1180, and -1190 utility radio 
switches manufactured by Scientific-Atlanta, Inc., Atlanta, Ga., and the 
type REMS-100 radio switch manufactured by General Electric, King of 
Prussia, Pa. These systems incorporate an FM receiver which can receive a 
transmittal up to about 25 miles from a transmitter site. The transmitter 
issues commands to temporarily remove power from a selected load. This 
self-contained receiver is typically mounted on or immediately adjacent to 
the electrical loads under control, and receives its power from the line 
that feeds the controlled loads. Switches, jumpers, or other means 
contained within the receiver configure the receiver to respond only to a 
particular address or set of addresses, so that different geographical 
areas, types of appliances, or numbers of consumers may be separately 
controlled. 
A particular problem with these separate remotely-controllable radio 
switches for electrical load management is testing of individual receivers 
for responsiveness. In particular, for effective load management the 
utility must develop a high degree of certainty that selected electrical 
loads will be removed when the commands are transmitted. If certain 
receivers are malfunctioning or are located in fringe reception areas 
wherein command signals may not reliably reach the receivers, there will 
be uncertainty whether a given command to reduce a load in an emergency 
situation will remove enough of the load to prevent a brown-out or other 
potentially more serious power interruption. 
In the above-described General Electric REMS-100 radio switch, an optional 
light-emitting diode (LED) is provided for test purposes. The receiver is 
responsive to receipt of a particular transmitted test command to 
illuminate the LED, and as meters are manually read by the utility, the 
LED can be checked. This test function allows a check of correct wiring of 
the receiver, correct operation of the receiver, and a check on the radio 
signal, and remains on indefinitely until commanded off or until loss of 
power, and provides no other indicating function. 
A handheld transmitter may be used for testing these receivers, but 
verifying the correct and reliable operation of the receiver requires a 
check of the system signal propagation properties. Thus sending test 
signals from the central utility transmitter, with the response indicated 
at each receiver site, is preferable for testing. However, the REMS-100 
receiver only has one indicator light for a one-time test which is 
verified later by the utility. There is also no provision for testing any 
function other than correct wiring and simple yes-or-no one-time receipt 
of the particular test command by the receiver. 
The particular REMS-100 load reduction receiver described above does 
however include a built-in volatile memory for maintaining an on-going 
record of valid messages received. This record is reset to zero by a 
particular predetermined incoming radio message, or upon power loss and 
restoration. Statistical data related to the number of load shedding 
commands provided to a particular receiver may be counted and retained in 
the volatile memory. This information is valuable in evaluating system 
performance, fringe area performance, and expansion coverage. However, the 
counting of the stored messages in the volatile memory entails opening of 
the receiver enclosure and placing an external probe on certain pins of 
the internal memory counter. Opening of the unit requires removal of the 
utility security tags or seals, and results in inconvenience to meter 
readers who must first remove the security tag, open the enclosure, 
connect a reading device to the memory, remove the connector after reading 
the memory contents, close the enclosure, and replace the security tag. In 
addition to risking the integrity of the circuitry by manual placement of 
a probe onto the pins of the circuits, this procedure involves the 
expenditure of a great amount of time, effort, and money in opening the 
box, reading the memory counter, and replacing the security tag or seal. 
Accordingly, there is a need for a method of testing load management system 
receivers quickly and inexpensively and without inconvenient procedures 
such as breaking security tags or seals, risking the physical integrity of 
the circuitry, or adding costly or complex circuit components into the 
receiver. 
While data displays are known in the art, and could easily be provided at 
each receiver for displaying more comprehensive testing information, 
complex data displays such as digital LED or liquid-crystal information 
displays are expensive and would require modifying the receiver enclosure 
so that the data display could be viewed from the exterior of the receiver 
enclosure. 
SUMMARY OF THE INVENTION 
The present invention overcomes these and other problems in monitoring and 
testing prior art load management system receivers by providing an 
improved method and apparatus for testing and monitoring the operation and 
configuration of such receivers. In the preferred method and embodiment, a 
utility employee such as a meter reader uses a hand-held display unit, 
which includes a low power transmitter, to stimulate the receiver to 
optically transmit operational and testing data via an optical data link 
to the display unit. Advantageously, the present invention utilizes a 
preexisting light-emitting display at the receiver for communicating more 
extensive data concerning the testing and operational parameters of a 
receiver to the hand-held display unit, which displays the information to 
an operator. 
In another embodiment, a preexisting local oscillator in the receiver 
circuitry is modified to take advantage of the stray RF transmissions 
provided by the oscillator. The data is transmitted via an RF radio link 
from the receiver to the hand-held unit by modulating the local oscillator 
in the receiver. 
Briefly described, the present invention comprises an improved status 
display method and apparatus for an electrical utility load management 
system receiver. The existing internal memory of the receiver control 
microcomputer is employed to store status data related to a plurality of 
parameters of operation or testing of the receiver. A predetermined status 
inquiry command signal transmitted from a hand-held display unit causes 
the receiver to retrieve the stored status data from the memory. The 
retrieved status data is then formatted into a communications format for a 
data link, and transmitted via the receiver's existing light-emitting 
display or RF oscillator. 
In both disclosed embodiments, a transportable hand-held display and 
transmitter unit is responsive to receive the transmitted status data, and 
to convert this received status data into a form readable by an operator 
of the hand-held unit. 
Advantageously, the receiver of the present invention allows the retrieval 
and display of status data without breaking or removing the utility 
security seal or tag, since the data is transmitted through the 
preexisting light emitting devices, whose original function was only to 
provide an indication of the current status of the radio switch, or 
through a preexisting local RF oscillator, whose original function was 
only to aid in the demodulation of signals transmitted to the receiver. 
More particularly described, the present invention comprises a display unit 
including a transmitter for transmitting a coded command signal having 
address and command information to a load management receiver. Each of the 
receivers includes means for decoding the command and address signals, and 
is responsive to the decoded command signals for removing an electrical 
load from the electrical distribution system. A memory in each of the 
receivers stores data related to the operation of the receiver, for 
example, the number of transmissions of a predetermined test command 
signal from the utility central transmitter, the time elapsed since power 
loss or receipt of a predetermined reset command, or the number of load 
control functions commanded and provided by the receiver within a 
predetermined time period. 
In addition, information concerning the configuration of the receiver is 
provided in the disclosed embodiment for display to the operator of the 
hand-held display unit. For example, programmed address information, cold 
load pick up information, relay time out periods, and other programmed 
parameters are stored and transmitted to the display unit so that the 
operator can observe the coded address for the particular receiver being 
tested, the sequence of function provisions for a cold load pick up, and 
the delay time period before reconnection of a given load to the 
distribution system. 
A predetermined status inquiry command signal from the display unit causes 
the receiver to retrieve the status data from the memory, and transmit the 
retrieved status data in a predetermined communications format either on 
the light-emitting display or via the "transmitter" of the modified RF 
oscillator. In the preferred embodiment, the display unit is small and 
transportable, and transmits the status inquiry command signal at lower 
power so as to stimulate only a single, near-by receiver. An optically 
responsive circuit or an RF receiver tuned to the frequency of the 
modified local oscillator is provided in the display unit for receiving 
the optically transmitted status data from the receiver. The received 
status data is then converted to a format for display to the operator of 
the transportable unit. In the preferred embodiment, the optically 
responsive element on the transportable display unit is engaged with the 
light-emitting display on the receiver to receive the transmitted status 
data within an extremely short period of time, typically less than 1/2 
second. 
Accordingly, it is an object of the present invention to provide an 
improved electrical utility load management receiver monitoring and 
testing method. 
It is another object of the present invention to provide a load management 
system testing method which does not require breaking or removal of the 
utility security tags or seals at the sites of load management receivers. 
It is another object of the present invention to provide an improved load 
management receiver testing system which allows the display of more 
detailed information pertaining to the operation and configuration of the 
receiver. 
It is another object of the present invention to provide a method for 
testing a load management receiver which does not require any physical 
modifications to the enclosure of the receiver, or the addition of 
expensive data display devices at each receiver. 
It is another object of the present invention to provide a system for 
testing a load management receiver which allows the monitoring of a 
greater number of parameters of operation of the receiver than prior art 
methods, such as the number of operations of particular control functions, 
the number of test functions, elapsed time, and configuration information. 
These and other objects, features, and advantages of the present invention 
may be more clearly understood and appreciated from a review of the 
following detailed description of the disclosed embodiment and by 
reference to the appended drawings and claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, in which like numerals indicate like 
elements throughout the several figures, FIG. 1 illustrates an electrical 
utility load management radio switch or receiver 10 constructed in 
accordance with a first embodiment of the present invention, and a 
hand-held transportable display unit 12 for stimulating the receiver 10 to 
retrieve data pertaining to the operation of the receiver. In the 
preferred embodiments, the receiver 10 is a type DCU-1120, -1170, -1180, 
or -1190 radio switch manufactured by Scientific-Atlanta, Inc., whose 
microcomputer program has been modified as disclosed herein. Those skilled 
in the art will understand that this type load management receiver 
includes a highly sensitive FM radio receiver 32 (FIG. 3) which can 
receive a radio transmittal up to 25 miles or more from a transmitter 
site. Typically, the receiver 10 is connected via wires 14 to the utility 
electrical power distribution system and to various electrical loads at a 
customer site. 
The radio switch 10 is configurable to control up to four different 
electrically separate loads by a plurality of control means such as relays 
or triac switches, so that different types of loads at the consumer's 
location can be controlled. For example, air conditioners and other types 
of loads considered non-essential may be controlled by one relay, while 
more essential electrical service for refrigerators and the like may be 
controlled by another circuit. These four controlled loads are frequently 
referred to as "control functions". 
An electrical utility typically provides a security seal or tag 15 to 
discourage and monitor tampering. The preferred receiver 10 includes an 
internal memory counter for maintaining a record of messages received. In 
the prior art, in order to read the contents of this memory, the security 
tag 15 must be removed, and unit opened to reveal a connector (not shown). 
An external probe is placed on the connector to read the memory contents. 
Needless to say, it is undesirable to require removal and replacement of 
the security tag in order to monitor and test the operation of the 
receiver 10. 
The receiver 10 shown in FIG. 1 further includes a light-emitting diode 
(LED) display 16 as an indicator of operation. In the usual configuration, 
a red LED is provided as an indication of provision of control function 
#1. Optionally, a green LED is provided in the receiver for purposes of 
indicating a "PROP CHECK" test function. The PROP CHECK function consists 
of an individual, group, or all-call (scram) address plus a test function 
command. The green test function LED lights without any load shedding 
occurring, and merely provides an indication that a particular 
predetermined command has been transmitted and correctly received and 
decoded by the receiver. Typically, a single message is transmitted by the 
utility on a certain day. As customer meters are manually read by the 
utility, the PROP CHECK LED is checked for illumination. If the light is 
illuminated, it is an indication that the particular receiver being 
checked has been correctly wired, and is correctly operating to receive 
commands via the radio link. 
In the first preferred embodiment of the present invention, the LED 16 is 
employed to optically transmit data pertaining to the operation of the 
receiver to the hand-held display unit 12. 
Still referring to FIG. 1, the display unit 12, seen from the rear, 
comprises an optical receiver 20 which is operatively positioned over the 
LED 16 when it is desired to read the status data from the receiver. A 
push button S1 on the top of the display unit 12 actuates a low-power 
transmitter contained within the display unit to provide a predetermined 
status inquiry command radio signal to the receiver, which is then 
responsive to retrieve stored status data and modulate the data to the LED 
16. The light from the LED is received by the optical receiver 20, and 
then displayed to the operator of the display unit 12. 
Referring now to FIG. 2, the front of the hand-held display unit 12 is 
illustrated. The display unit includes a digital data display 22 for 
displaying the information received from the receiver 10. Although it will 
be understood that other types of status data may be provided, in the 
disclosed embodiment, the parameters of operation tested and monitored 
include the number of operations of each of the four control functions, 
designated F1 through F4, the number of test signals received, and the 
elapsed time since power loss or reset. It will be understood that while 
more or fewer parameters may be monitored, such as more or fewer functions 
may be provided or tested by a receiver, the preferred receiver employed 
in the disclosed embodiment provides four control functions, thereby 
allowing the removal or shedding of four different circuits from the 
electrical distribution system. Thus, it will be appreciated that the data 
display 22 displays in digital Arabic numerals the number of operations of 
each of the four control functions (F1-F4), the number of test signals 
received (TESTS), and the elapsed time (TIME) since power loss or reset, 
in one consolidated, easy-to-read format. It will thus be appreciated that 
a utility meter reader or other operator can retrieve the status data of a 
particular customer's receiver at the time the customer's meter is read, 
and the recorded status data compared to the number of function control 
commands or test commands provided by the main utility transmitter, so 
that a more comprehensive monitoring of the operation of the utility load 
management system may be accomplished. 
In addition, it is specifically contemplated that information concerning 
the configuration of the receiver being addressed may also be provided for 
display to the operator of the hand-held display unit. By causing a 
receiver to provide information about the configuration of itself for 
display on the display unit, a meter reader or other display can examine 
the particular functional aspects of the receiver noninvasively. For 
example, programmed address information, cold load pick up information, 
relay time out periods, and other programmed parameters related to the 
receiver configuration may be stored and transmitted to the display unit. 
This allows the operator to observe, respectively, the radio address code 
for the particular receiver being tested, the sequence of function 
provisions for a cold load pick up, and the delay time period before 
reconnection of a given load to the distribution system after 
disconnection. This configuration information may be displayed on the data 
display 22 either by time multiplexing in the predetermined display areas 
labelled "F1" through "F4", "TESTS", and "TIME" in FIGS. 2 or 3, or 
alternatively by providing a larger data display with more area for 
display of information. 
The display unit 12 further includes an audible buzzer or beeper 24 for 
providing an audible signal to the operator, which will be described in 
greater detail below. 
Referring now to FIG. 3, the disclosed embodiments of the load management 
system receiver 10 and the transportable display unit 12 will be 
described. The receiver 10 comprises an antenna 30 for receiving 
transmitted radio messages from a main utility transmitter 31. The 
structure and operation of an exemplary electrical load management system 
comprising a utility transmitter and a plurality of receivers for 
receiving coded information by radio from the main utility transmitter is 
shown in U.S. Pat. No. 4,190,800 to Kelly, Jr. et al., assigned to the 
same assignee as the present invention, the disclosure of which is 
incorporated herein by reference and made a part hereof. As described in 
this patent, the transmitted signal from the main utility transmitter 31 
includes both address and command information which is decoded at each of 
the receivers. Those receivers which have been addressed utilize the 
command information to selectively remove electrical loads from the 
distribution system. The address information informs the customer of the 
existence of a peak load condition and/or controls the operation of the 
power consuming devices and/or electric meter connected to the receiver. 
In the preferred embodiment of the present invention, as illustrated in 
FIG. 3, a radio frequency (RF) receiver/demodulator 32 receives the radio 
frequency command signal from the antenna 30 and is responsive to 
demodulate the transmitted command signals and provide the demodulated 
signals to a microcomputer 35. The microcomputer 35 is programmed to 
respond to command signals for the particular address for the particular 
receiver to provide the commanded control function. The microcomputer 35 
provides control signals over lines 36 to an isolation and relay driver 
circuit 40, which drives the coils K1-K4 of a relay circuit 41. As will be 
understood by those skilled in the art, actuating the coils K1-K4 of the 
relay circuit 41 trips the contacts T1-T4, respectively, of the relay to 
connect or disconnect electrical loads Z1-Z4, respectively, from the AC 
electrical power distribution lines 42. Although not shown in FIG. 3, it 
will be understood that power for the receiver 10 may be drawn by a 
transformer connected in parallel to the AC lines 42. 
Microcomputer 35 also provides a control signal on line 44 to a status 
display driver circuit 45, which controls the illumination of LED 16. As 
described above, the receiver 10 is operative to illuminate the LED to 
provide an indication that a control function is being provided (typically 
function #1, indicating actuation of relay contacts T1), or to illuminate 
an optional separate LED as an indication of receipt of the PRO CHECK test 
function. 
Also illustrated in FIG. 3 in block diagram form are the components of the 
transportable display unit 12. The preferred embodiment of the display 
unit 12 comprises a microcomputer 50 as the central controller of the 
display unit. The microcomputer is connected to a lower power FM radio 
frequency transmitter 51, which drives an antenna 52. Such FM transmitter 
circuits are known in the art, and will not be described further herein. 
However, it should be understood that the transmitter 51 employed in the 
disclosed embodiment is operative to transmit a predetermined status 
inquiry command signal at low power, in order to ensure that the display 
unit 12 only triggers display of the status information from a receiver in 
close proximity. Those skilled in the art and familiar with the structure 
of the preferred receiver 10 will understand that the "status inquiry" 
command optimally comprises a signal such as the "all call" or "scram" 
address plus a particular predetermined test function code. 
The microcomputer 50 is further operative to control the data display 22. 
In the preferred embodiment, the data display 22 comprises a type LM016 
liquid crystal display (LCD) manufactured by Hitachi America, Ltd., San 
Jose, Calif. Those skilled in the art will understand that this type LCD 
display includes electronics which enable it to receive data in parallel 
eight-bit ASCII format, which is then internally manipulated to create the 
digital Arabic numeral display as shown in FIGS. 2 and 3. 
Microcomputer 50 is also connected to an optical receiver circuit 20, which 
is described in more detail in connection with FIG. 5. The optical 
receiver 20 is operative to receive optically transmitted data from the 
LED 16 of the receiver 10. 
A timing and control circuit 55 is also operatively connected to 
microcomputer 50, and is operative to detect the actuation of push button 
switch S1 to begin operation of the microcomputer 50. A battery BT1 
connected to the timing and control circuit 55 powers the display unit 12. 
Referring now to FIG. 4, the construction of the timing and control circuit 
55 will be described in more detail. Actuation of the switch S1 controls 
the provision of power to the other components in the display unit, and 
causes the microcomputer 50 to begin execution of its program (the flow 
chart for the program of microcomputer 50 is illustrated in FIG. 6). When 
an operator depresses switch S1, ground potential is imposed at node 61 
and provides a conduction path for capacitor C1 to discharge through 
resistor R1 and diode D1 to ground. Also, capacitor C2 discharges. 
Capacitor C1 is normally held charged through resistors R1, R2 by the 
battery BT1, which in the preferred embodiment is a conventional nine volt 
battery. Capacitor C1, after discharging, is recharged through resistor R2 
at a time constant of about 30 seconds or more, to power down the 
circuitry as will be described below. 
When capacitor C1 is discharged, a low will occur at the input of an 
inverter circuit 62, whose output is connected thorough a resistor R3 to 
the base of an NPN transistor Q1. Unless otherwise noted, all gates and 
the like employed in the preferred embodiment are CMOS to limit power 
consumption. Transistor Q1 then begins conducting, and allows power to be 
provided on line 63 to the POWER input of LCD display 22. The BIAS input 
of the display 22 is connected to the negative terminal of battery BT1, 
while the display ground is connected to the ground of the timing and 
control circuit 55. 
Diode D2 connected between the negative terminal of battery BT1 and the 
ground plane of the timing and control circuitry 55 provides a negative 
potential to the BIAS input of the display 22 of approximately 0.7 volts 
below the ground potential of the timing and control circuit, which those 
skilled in the art will appreciate enhances the appearance of the liquid 
crystal display. 
A zener diode D3 connected between the base of transistor Q1 and ground 
limits the voltage appearing at the base of transistor Q1. 
The low appearing at node 61 from actuation of switch S1 also causes a 
low-going pulse to occur at one input of a NAND-gate 65. The low on node 
61 is coupled to gate 65 through capacitor C3, which is quiescently held 
high through resistor R4. The output of NAND-gate 65 is connected to one 
input of a second NAND-gate 66, whose output is provided to the other 
input of NAND-gate 65 to form a latching circuit or flip-flop 67 known to 
those skilled in the art. The output of flip-flop 67 is provided on line 
71 through a resistor R6 to node 73 and the base of an NPN transistor Q2. 
In the preferred embodiment, transistor Q2 is a Darlington transistor, the 
collector of which is connected to the nine-volt battery and the emitter 
of which is connected to the power supply V.sub.cc of the microcomputer 
50. When a high appears at 71 when flip-flop 67 sets, transistor Q2 
conducts, and provides power to the microcomputer. 
The cathode of a 5.6 volt zener diode D3 is connected at a node 73 between 
the base of transistor Q2 and the base of another NPN transistor Q3, and 
limits the voltage appearing at the base of Q2. A resistor R7 is connected 
between the base of Q3, the anode of D3, and ground. As known to those 
skilled in the art, the preferred CMOS circuitry employed in the disclosed 
embodiment operates over a fairly wide voltage range, but the 
microcomputer 50 employed in the preferred embodiment, a type 8748 
manufactured by Intel Corporation, Santa Clara, Calif., requires at least 
five volts for reliable operation. In the event that battery BT1 becomes 
weak so that the high provided at node 73 is insufficient to break down 
the zener, transistor Q3 will not conduct. Stated otherwise, so long as 
the voltage at 73 is sufficient to break down zener diode D3, the base of 
transistor Q3 will be biased, and Q3 will conduct. 
The collector of transistor Q3 is connected to line 74, which is connected 
to one of the inport ports, PORT 2, of the microcomputer 50, while the 
emitter is grounded. Thus, it will be appreciated that when transistor Q3 
is on, a low will appear on line 74 at the PORT 2 input for sensing 
battery operation. In the vent the microcomputer program detects a high on 
line 74, steps for signalling a "battery low" condition are executed. 
The power-down operation of the microcomputer 50 is as follows. One of the 
data bus (DB) lines of microcomputer 50 is provided through a resistor R8 
and capacitor C4 to the base of a NPN transistor Q4. The cathode of a 
diode D4 is connected also to the base of transistor Q4. The emitter of 
transistor Q4 is grounded, while the collector is pulled up to nine volts 
through resistor R9 and is connected to the input of an inverter circuit 
75. The output of inverter 75 is connected to the remaining input of 
NAND-gate 66, the reset input of the flip-flop 67. 
The power to microcomputer 50 remains until one of two occurrences: (1) the 
microcomputer 50 powers itself down, or (2) an RC network times out. In 
the first situations, microcomputer 50 will shut itself down at the 
conclusion of its program (as indicated in FIG. 6). The microcomputer 
places a low on the data bus line DB, which turns transistor Q4 off. With 
Q4 not conducting, the input to inverter 75 is high, placing a low at the 
input of the flip-flop 67, which drives the output of the flip-flop at 
line 71 low. If line 71 goes low, the bias from the base of transistor Q2 
will be removed, and turn off power to the microcomputer. 
The other mechanism for powering down the microcomputer is as follows. When 
microcomputer 50 begins its operation, the data bus line DB is brought 
high under program control, placing a bias at the base of transistor Q4, 
turning the transistor on and placing a low at the input of inverter 75. 
Those skilled in the art will understand that this provides a high to the 
input of the NAND-gate 66, which together with a high on line 71 keeps the 
flip flop 67 set and transistor Q2 conducting. However, capacitor C4 will 
charge through resistor R8, and will subsequently remove the bias from 
transistor Q4, causing the transistor to turn off. It will thus be 
appreciated that this resets the flip-flop 67, and removes power from the 
microcomputer. In the preferred embodiment, the R8/C4 time constant, which 
is dependent on the beta of transistor Q4, is about 1-2 seconds, which 
allows ample time for the microcomputer to execute its program. It should 
also be noted that the power supply to the input V.sub.cc of microcomputer 
50 is about five volts, due to the dual diode drops across the Darlington 
structure of transistor Q2, the voltage drop across the zener diode D3, 
and the base-emitter drop of transistor Q3. 
In the preferred embodiment, microcomputer 50 is a type 8748 eight-bit 
microcomputer manufactured by Intel Corporation. It will be appreciated by 
those skilled in the art that other types of microcomputer circuits can be 
substituted for the microcomputer used in the preferred embodiment with 
equally satisfactory results. The type 8748 is particularly suitable for 
use in the present invention because it includes an ultraviolet-erasable 
programmable read-only memory for program storage, a 64.times.8 data 
memory, and an on-board timer/counter. Microcomputer 50 also includes a 
pair of bidirectional output ports, PORT 1 and PORT 2, which are eight-bit 
quasi-bidirectional data ports. 
Still referring to FIG. 4, the eight lines of PORT 1 are provided to the 
data input of the display 22. It will be appreciated by those skilled in 
the art that the microcomputer 50 is operative to provide ASCII data to 
the display 22. 
One of the PORT 2 lines is provided to beeper 24, shown in FIG. 3. It will 
be appreciated that microcomputer 50 can provide an audible signal to an 
operator by providing a signal on the selected PORT 2 line. Another of the 
PORT 2 lines is provided to the transmitter 51. It will also be 
appreciated that particular predetermined all-call or status inquiry 
command signal may be provided in digital form to the transmitter 51, 
which is responsive to transmit the encoded signal to the receiver. 
The optical receiver 20, illustrated in more detail in FIG. 5, is provided 
to the T1 test input of the microcomputer 50, shown in FIG. 4. It will be 
appreciated that the microcomputer receives the transmitted signals from 
the receiver 10 by monitoring the signal activity on the test input T1. 
Referring now to FIG. 5, the optical receiver circuit 20 comprises a 
photoconductive cell 80 for detecting the light emitted by the LED 16 
(FIG. 3). In the preferred embodiment, the photoconductive cell 80 is a 
cadmium sulfide photocell such as a type VT-721H manufactured by Vactec, 
Inc. of St. Louis, Mo. Those skilled in the art will appreciate that the 
preferred photoconductive cell has a wide dynamic range for high speed 
switching and operates satisfactorily in high ambient light. 
The photoconductive cell 80 is biased by the five-volt power supply of the 
display unit 12, and voltage fluctuations caused by the detection of light 
are coupled thorough a capacitor C10 and resistor R10 to the inverting 
input of an operational amplifier A1. Capacitor C10 is preferably of a 
value to transmit the relatively high frequencies of the transmitted data 
from the load management receiver and to block 60 HZ power line 
interference which may be present. A feedback resistor R11 connected 
between the output of amplifier A1 and the inverting input provides a gain 
of about 100. Those skilled in the art will understand that the structure 
of amplifier A1 is conventional. 
The output of amplifier A1 is provided through a resistor R12 to the base 
of an NPN transistor Q5. Transistor Q5 and its related components comprise 
a conventional common-emitter amplifier stage. The emitter of transistor 
Q5 is connected to ground through RC network R13, C13, while the collector 
is connected through resistor R14 to the five volt power supply. 
The collector of Q5 is also connected through resistors R15, R16 to the 
inverting and noninverting inputs, respectively, of an amplifier A2 
configured as a voltage comparator/Schmitt trigger. The output of 
amplifier A2 is fed back through resistor R17 to the noninverting input. 
Those skilled in the art will understand that the preferred configuration 
for amplifier A2 is to square-up input signals provided to it through the 
transistor Q5. 
The output of amplifier A2 is provided to the test input T1 of the 
microcomputer 50 in FIG. 4. 
In the preferred embodiment, the encoding scheme for data transmission from 
the load management receiver 10 to the hand-held display unit 12 is a 
bi-phase encoding format such as a Manchester code which allows 
transmission of a synchronized clock reference for the data to be 
transmitted together with the data. Inasmuch as bandwidth requirements are 
not of particular concern in the present invention, other types of 
encoding formats, such as frequency shift keying (FSK) or pulse width 
modulation (PWM), may also be used with equal success. The clock frequency 
of the microcomputer 50 should be high enough to insure that the program 
loop which tests the test input T1 for a high or low can properly detect 
and decode the Manchester code. 
Turning now to FIGS. 6 and 7, the general operation of the circuitry 
comprising the preferred embodiment will now be described. FIG. 6 is a 
flow chart diagram which illustrates a sequence of steps which may be 
embodied as a program for the microcomputer 50 in the display unit 12. 
Similarly, FIG. 7 is a flow chart diagram which illustrates a sequence of 
steps which may be embodied as a program for the microcomputer 35 in the 
load management receiver 10. Those skilled in the art will now understand 
and appreciate that apparatus as described herein for transmitting a 
predetermined status inquiry command signal from a display unit to a load 
management receiver, for causing the receiver to transmit encoded status 
data via a preexisting LED indicator, for receiving the transmitted status 
data and decoding same, and for displaying the decoded information in a 
format for an operator, may be constructed by circuits comprising digital 
and analog hardware, or by a preferred embodiment, as disclosed herein, 
using programmed microcomputers together with peripheral digital and 
analog circuitry. 
It will be understood that the embodiment disclosed herein is merely 
illustrative and that the functional equivalents of the microcomputers 35, 
50 may include other devices including digital hardware, firmware, or 
software, which are capable of performing the described functions and 
sequences in the present invention. It will be further appreciated that 
the microcomputers 35, 50 may be programmed to perform the steps 
illustrated in FIGS. 6 and 7. 
Starting first with FIG. 6, there will be described the sequence of steps 
for operation of the display unit 12. The first step taken in the software 
for the microcomputer 50, shown at 100, is to start operation of the 
microcomputer 50. It should be understood that the operator of the display 
unit 12 will depress the switch S1, which causes power to be provided to 
the microcomputer 50. Those skilled in the art will appreciate that when 
power is provided to microcomputers such as the type 8748 employed in the 
preferred embodiment, a start-up or initialize routine is executed, which 
initializes and clears registers and begins operation of the program. 
After these initializing routines, typically taken at step 100, the 
predetermined status inquiry command signal is transmitted at 101. 
It should further be understood that in normal operation, and as 
illustrated in FIG. 1, the optical receiver 20 of the display unit 12 is 
placed in close operative proximity to the LED 16 on the receiver 10 which 
is to be monitored or tested. The switch S1 is then depressed, and the 
optical receiver will then be conditioned to receive the optically 
transmitted data. This step is illustrated at 102 in FIG. 6. 
At 103, the microcomputer executes a routine which attempts to decode the 
received information, it being understood that a Manchester code is 
expected in the preferred embodiment. It will be further understood that 
formatting information such as a header, a data stream, and finally a 
trailer such as a cyclic redundancy check (CRC) or other check bit scheme 
is employed in the preferred embodiment to insure that valid data is 
received from a light source. In the event that an improper format is 
detected by the microcomputer, the "NO" branch is followed to 104. The 
microcomputer 50 then causes the beeper 24 to emit a short single beep as 
an audible indication to the operator that for some reason valid data has 
not been received. Normally, at this point in the program, after the 
status inquiry command has been transmitted, the microcomputer will be 
expecting a properly encoded and formatted optically transmitted data 
stream, and if such a data stream is not detected, there is thereby 
provided an indication of a malfunction or other improper operation. 
In the event that the proper data format is detected, the "YES" branch from 
103 is followed to 105. At 105, the header and trailer information of the 
data is stripped, and the data received by the microcomputer separated and 
formatted for display on the display 22. As described above, this entails 
converting the received data into ASCII format for the display 22. 
At 106, the microcomputer tests the PORT 2 input on line 74 to determine if 
the power supply battery is beginning to deteriorate. In the event that 
the power supply is detected as weak, the "YES" branch is followed to 107, 
and a single asterisk (*) is provided to the display 22 in addition to the 
data as described below. This provides a visual indication to the operator 
that the battery requires replacement. 
In the event that the power supply is deemed adequate, or after an asterisk 
is output to the display as a weak battery indicator, step 108 is reached, 
and the now-formatted data is provided to the display 22. In the preferred 
embodiment, a series of three short beeps are also provided as an audible 
indication that the data is available for viewing and recording. 
After either steps 104 or 108, the microcomputer 50 then at 109 provides a 
signal on the data bus line DB to cause power to be removed from the 
circuitry. The program then enters an endless loop, until power is removed 
via flip flop 67 and transistor Q2. Power remains connected to the display 
22 through transistor Q1 for a longer time period as previously described 
to allow observation of displayed data. 
Referring now to FIG. 7, there will now be described the sequence of steps 
for the microcomputer 35 in the load management receiver 10. As described 
above in connection with FIG. 1, the microcomputer 35 is employed as the 
central controller for driving the isolation and relay drivers 40 to 
selectively remove loads from the electrical distribution system, to 
illuminate the LED 16, and to decode commands received from the RF 
receiver/demodulator 32. It should be understood that the microcomputer 35 
in the disclosed embodiment, provided in the type DCU 1180 receiver, is 
preprogrammed to provide these decoding and control functions. These 
functions will not be described herein. However, in the preferred 
embodiment, the program for the microcomputer 35 is modified to make the 
microcomputer responsive to a particular predetermined status inquiry 
command signal to modulate the LED 16 to transmit retrieved status data. 
Accordingly, it will be understood that the program for the microcomputer 
35 is altered to perform the sequence of steps illustrated in FIG. 7. 
For purposes of describing FIG. 7, it should be further understood that the 
program therein illustrated in flow chart form may be implemented as an 
interrupt routine, a subroutine, or as part of the normal program flow for 
the microcomputer 35. For the discussion which follows, it will be assumed 
that the microcomputer 35 is normally operative to decode and execute 
commands transmitted to it by the main utility transmitter during normal 
operation, and to be responsive to execute certain of the steps of FIG. 7 
only upon detection of a predetermined status inquiry command signal. 
Starting at 120, after any initializing or stack-saving routines commonly 
executed in microcomputer programming, the microcomputer 35 is responsive 
to detect decoded digital signals being provided to it from the RF 
receiver/demodulator 32 (FIG. 3), at 121. The digital signals provided to 
the microcomputer are first compared to the preprogrammed address 
information at 122, to determine if the particular receiver unit is being 
addressed. If proper address information is not decoded, the program flow 
returns to 121, to await receipt of another RF command. 
In the event that the microcomputer 35 detects that it is being addressed, 
the "YES" branch from 122 is followed to 123. At this step, the 
microcomputer is responsive to compute the cyclic redundancy check (CRC) 
data or other data integrity checking scheme. If at 124 the information 
received is improper, the program returns to 121. On the other hand, if 
the CRC is determined to be proper, the "YES" branch is followed to 129. 
At 129, microcomputer 35 has now determined that it has been addressed, and 
that it has received a valid command due to the detection of a valid CRC 
test. At 130, the command received is compared to a special status inquiry 
command. If this command is not detected, microcomputer 35 then will 
execute the particular command received at 131, which will be one of the 
normal control or command functions provided by the receiver 10 in normal 
operation. 
If the special status inquiry command signal has been received, however, 
then at 132 the microcomputer begins a sequence of steps which retrieves 
the status information from memory and transmits it through the optical 
data link, since the special status inquiry command signal in normal 
operation is only transmitted by a hand-held display unit 12. In order to 
accomplish these tasks, the microcomputer at 132 first disables any timers 
or other microcomputer features which might disrupt the communications 
transmission. At 133, the microcomputer retrieves from memory the status 
information described above. It will be recalled that in the preferred 
embodiment, this status information comprises the number of provisions of 
control functions F1-F4, a number of test transmissions received by the 
receiver, and the elapsed time since power loss or a provision of a reset 
command signal by the main utility transmitter. It will be understood that 
this status information has been prestored in a register of the 
microcomputer 35, or in an auxiliary memory provided for storage of this 
information. 
After the status information has been retrieved, at 134 the microcomputer 
formats the information in a predetermined communications format 
receivable by the display unit 12. As those skilled in the art will 
understand, optical communications links typically comprise a preamble or 
series of digital signals which allow synchronization by the display unit 
12 to receive the optically-transmitted data. In the preferred embodiment, 
it will be recalled that a Manchester code is employed, and that use of 
this or other bi-phase communications formats requires the transmission of 
a predetermined number of bits of synchronizing information. 
In the disclosed embodiment, and as illustrated in FIG. 8, the preferred 
communications format comprises a preamble of a predetermined number of 
preamble bits, fifty in the disclosed embodiment, each preamble bit having 
a bit of cycle time of 160 microseconds, followed by the data to be 
displayed. The data following the preamble is transmitted at a bit or 
cycle time of 480 microseconds, and the first or "start" bit is always a 
"1". The preamble bits allow time to synchronize the microcomputer (the 
preamble bits are thrown out), and to establish quiescent operating levels 
for the components in the optical receiver circuitry 20. As will be 
understood by those skilled in the art, the Manchester code illustrated in 
FIG. 8 is decoded by determining the presence or absence of a transition 
within the 480 microsecond cycle time, with the absence of a transition 
indicating a "1" and the presence of a transition indicating a "0". It 
will of course be understood that in FIG. 8 a low level indicates that LED 
16 is not illuminated, while a high level indicates that the LED is lit. 
In radio switches having more than one LED, it will be further understood 
that a plurality of LED's may be simultaneously modulated in parallel as 
described to obtain greater light output, and thus improve signal-to-noise 
ratios under some circumstances. 
After provision of the preamble, the microcomputer 35 at step 135 transmits 
in serial fashion, in the above-described Manchester code format, the 
status information which has been previously retrieved. Also, at step 135, 
it should be understood that any CRC which may be added as trailer is 
computed and transmitted as well, so that the display unit 12 can verify 
receipt of the data. 
At 136, the microcomputer 35 restarts the timer and restores any stack 
information which had been set aside prior to entry of the status inquiry 
command routine described herein. Then, the program returns to 120, or 
exits the interrupt or other subroutine employed to implement the 
herein-described status information transmission routine. 
In a second preferred embodiment of the present invention, advantage is 
taken of the RF energy radiating characteristics of preexisting circuitry 
in the RF receiver/demodulator 32 in the receiver 10 to provide an RF data 
link for transmission of the retrieved status data. Those skilled in the 
art will understand that many conventional receiver circuits employ local 
RF oscillators in the demodulator circuitry to facilitate frequency 
conversion, and that stray RF signals emanating from these local 
oscillators can be detected for distances as great as several hundred feet 
from the receiver. In the second embodiment, advantage is taken of this 
stray radiating capability to create an RF data link for transmission of 
the status data from the receiver 10 to the hand held display unit 12. The 
display unit accordingly is adapted such that the optical receiver 20 is 
replaced with an RF receiver/demodulator tuned to the frequency of the 
local oscillator to receive the data transmission. 
Referring now in particular to FIG. 9, there will now be described 
modifications to the receiver/demodulator 32 employed in the receiver 10. 
Typically, receiver circuits for use in receiver/demodulator 32 are double 
conversion type, the construction of which will be understood by those 
skilled in the art. Of course, it will be understood that other types of 
receiver circuits which have local oscillators that produce stray RF 
transmissions can also be employed with the modifications described 
herein. 
In the receiver/demodulator 32 employed in the disclosed embodiment, the 
receiving antenna 30 is connected to an RF amplifier 150, the output of 
which is connected to a mixer 151. Also connected to the mixer 151 is a 
first local oscillator 152 which oscillates at a frequency of RF-10.7 MHz, 
where RF is the transmission frequency of the FM encoded command signals 
to the receiver. The output of the mixer 151 is then provided through a 
bandpass filter 155 to a second mixer 156, which mixes the signal with the 
output of a second local oscillator 157, which oscillates at a fixed 
frequency of 10.245 MHz. The output of the mixer 156 is then filtered by 
bandpass filter 160. It will be appreciated that the resultant frequency 
difference from the output of the second mixer 156 is 10.7-10.245=455 KHz, 
the standard AM intermediate frequency. Thus, bandpass filter 160 is 
preferably 455 KHz. The output of filter 160 is provided to a detector 
stage 161, the output of which is the digital data stream provided to the 
microcomputer 35. 
Either the first oscillator 152 or the second oscillator 157 can be 
modified as described herein to utilize the oscillator as an RF signal 
source. Data from the microcomputer 35 is provided over a line 162 from 
the microcomputer to either the second local oscillator 157, or alternate 
to the first local oscillator 152 on line 162'. 
It will also be understood that a separate dedicated third oscillator or 
transmitter could be provided in the receiver 10 for the specific purpose 
of providing an RF data link to the hand held display unit 12. 
FIG. 10 illustrates the modifications to a typical oscillator circuit 152 
or 157, so as to modulate the oscillator to transmit data from the 
microcomputer to the display unit. First, it will be understood that 
without the use of shielding techniques, oscillators in receiver circuits 
radiate RF energy even without provision of a transmitting antenna. In 
most applications, there is no need to be concerned with the stray RF 
signal provided by such oscillators since the signal strength is only 
sufficient to be detected within a few hundred feet, and typically the 
frequencies are such that consumer electronic equipment will not be 
affected undesirably. 
The oscillator 152, 157 illustrated in FIG. 10 comprises an NPN transistor 
Q5 as the active component, with a feedback path provided from the emitter 
through capacitor C5 to the base of the transistor Q5. Resistor R10 serves 
as a load resistor, while capacitor C6 filters higher frequency components 
to ground. 
A crystal X1 is connected between ground and the base of transistor Q5 and 
is the prime frequency-determining component. A voltage divider comprising 
resistors R12, R13 provide biasing for the base of transistor Q5. An LC 
network comprising tunable coil L1 and capacitor C7 connected between the 
power rail and the collector of Q5 allows tuning of the oscillator's 
frequency. 
The previously-described components constitute a conventional oscillator 
circuit. The modifications to FSK modulate the oscillator are enclosed 
within the dotted block 168. A varactor diode VC1 is connected between 
ground and through a capacitor C8 to the base of transistor Q5. C8 is 
selected to limit the frequency "pull" of the circuit and prevent 
operation at frequencies substantially above the selected frequency. 
Varactor diode VC1 allows the capacitive loading on the crystal X1 to be 
varied as a function of a control voltage. 
The control voltage from the microcomputer is provided through a resistor 
R15 to the node between the varactor diode VC1 and the capacitor C8, and 
provides either a high or low voltage level to vary the capacitive loading 
to the crystal X1, thereby causing the crystal to oscillate at one of two 
selected frequencies. 
The first oscillator 152, if modified to serve as the "transmitter", is 
commonly known as a "tripler" in that the circuit operates at three times 
the desired local oscillator frequency. The crystal X1 is selected on the 
order of 47 MHz, and the output of transistor Q5 at the collector is on 
the order of 141 MHz. The line 165 from the oscillator is the radiating 
element. 
In the configuration illustrated, the radiated energy of the oscillator is 
strongest at the fundamental frequency of the crystal, namely, 47 MHz, and 
at related harmonics including 94 MHz and 141 MHz. It has been discovered 
that the signal strengths at the fundamental frequency and first two 
harmonics is sufficient for transmitting distances on the order of a few 
hundred feet. Thus, preferably the FM receiver in the hand held display 
unit 12 is responsive to signals at either 47, 94 or 141 MHz. 
In the case of the second or "fixed" local oscillator 157, which it will be 
recalled operates at 10.245 MHz, the signal at the collector of Q5 will be 
strongest at the fundamental frequency of the oscillator, that is, 10.245 
MHz. Accordingly, the receiver in the display unit should be tuned to this 
frequency if the second oscillator is modified to serve as the 
"transmitter" for the data link. 
It will be appreciated that the modulation technique described in the 
circuitry of FIGS. 9 and 10 is frequency-shifting (FSK) in that the 
oscillator 152, 157 is caused to shift between two frequencies, one of 
which represents a digital "0" and one of which represents a digital "1". 
It will be further understood that other modulation techniques can also be 
employed with equal success in the present invention, for example, 
amplitude modulation, phase modulation, audio frequency shifting (AFSK), 
or other techniques. However, it will be appreciated that the technique 
disclosed herein is particularly easy to implement since few modifications 
to the oscillator circuitry are required, in that only the components 
within the block 168 must be added to a conventional oscillator circuit in 
order to transform the oscillator into an FSK "transmitter". 
Another alternative easy-to-implement modification to the oscillator 152, 
157 is shown in dotted relief in FIG. 10 and comprises the addition of a 
diode D5 to the base of transistor Q5 to transform the oscillator into a 
continuous wave (CW) modulator, that is, on/off gating. It will be 
appreciated that by connecting the anode of the diode D5 to the base of 
transistor Q5, and providing a low or a high at the cathode from the 
microcomputer 35, the oscillator can be switched on or off to transmit 
data. 
It will also be understood that other techniques for data transmission 
between the receiver 10 and the hand held display unit 12 can be employed 
with equal success, for example sonic or ultrasonic techniques can be 
employed by connecting audible sound or ultrasonic transducers to be 
driven by the microcomputer 35 in the receiver 10, and by providing a 
corresponding receiver in the hand held display unit 12. In addition, 
magnetic coupling can be successfully employed, for example, by providing 
a coil to create a time-varying electromagnetic field as the 
"transmitter", and a corresponding coil as the "receiver" in the display 
unit to which the field is coupled. 
It will therefore be understood that other techniques may be employed to 
transmit commands from the display unit 12 to the receiver 10, for 
example, by substituting an optical, audio frequency, ultrasonic 
frequency, or other energy transmission device for the RF transmitter 51, 
and by providing a corresponding energy signal receiver circuit in the 
receiver 10. The important consideration is the provision of a 
bidirectional communications link between the display unit 12 and the 
receiver/remotely controllable switch 10 so that the receiver can be 
stimulated to retrieve prestored status data and transmit same to the 
display unit for display to the operator, without breaking or removing the 
utility seal or tag and without subjecting the operator of the display 
unit to electrical hazard through any hard-wiring techniques. 
The preferred embodiments of the present invention have been disclosed by 
way of example and it will be understood that other modifications may 
occur to those skilled in the art without departing from the scope and the 
spirit of the appended claims.