Note: Descriptions are shown in the official language in which they were submitted.
CA 02224963 1997-12-16
WIRELESS THERMOSTAT
FIELD OF THE INVENTION
This invention relates to thermostats. More specifically, it relates to wirelessand, in one embodiment, batteryless thermostats.
BACKGROUND OF THE INVENTION
Thermostats are common in almost all commercial and residential settings. It is
well known that thermostats are a vital control for HVAC systems. For the purpose of
simplifying the description and to increase the ease of understanding the invention,
10 Applicant will describe the invention for use in a residential home. However, it should
be understood that this invention is also applicable to commercial settings.
Most residential homes utilize a single thermostat which is located in an area
away from direct sunlight. The HVAC's heating and cooling units, such as a furnace, a
boiler or an air conditioner, are generally located in a different location such as in a
15 basement utility room or in the case of air conditioners and heat pumps, outside. The
thermostat is generally hardwired to the heating and/or cooling units, allowing for the
control of these devices by the thermostat.
When remodeling an older home, or in the case of upgrading a thermostat, the
process can be overly burdensome. To install the new thermostat, the party remodeling
20 or upgrading may be required to run new wiring to the heating and/or cooling units.
This process is extremely difficult if the retrofit installation involves plaster walls or
penetrating stone or brick.
A second disadvantage of most hardwired thermostats is that they sense
temperature in a single location of the home and are therefore unable to accurately
25 control the temperature in other rooms of the home. By way of explanation, in a home
which is a two-story home with a basement, if the thermostat is located in an upstairs
hallway, the thermostat is unable to accurately control the heating and cooling in the
basement. One solution which has been utilized is to locate thermostats in different
zones and provide damper controls for a zone-controlled HVAC system. However,
30 zone-controlled HVAC systems are quite expensive and often difficult to install, if not
prohibitive to install in established homes.
CA 02224963 1997-12-16
Applicant's invention provides a thermostat which is easy to install and does not
require hardwiring to the heating or cooling unit. Further, Applicant's invention enables
the owner of the home to accurately control the heating and cooling in whichever room
the owner of the home desires.
SUMMARY OF THE INVENTION
Applicant's invention is a wireless thermostat which communicates with the
HVAC unit via RF signals. The wireless thermostat allows for control of the heating or
cooling in a room specified by the occupant. The wireless thermostat is powered by
either long life batteries, or by high efficiency solar cells and a storage capacitor.
In one embodiment, the thermostat is capable of sending temperature and other
related thermostat information to a remote receiver normally located at the HVAC unit.
The tr~n~mi~ions are originated at the opening or closing of a mercury switch on a bi-
metal strip and contain digital coded information to identify the unit from other
potential units in the system. The receiver contains decoding circuitry to identify an
individual unit code and perform the previously established function.
In a more advanced embodiment, the RF circuitry would be integrated into a
setback thermostat and would have the capability of sending timing and temperature
data over the RF link to the HVAC receiving unit. Setback thermostats are well known
in the art. An example of setback thermostats can be found in U.S. Patent 4,314,665
issued to Michael R. Levine and hereby incorporated by reference. The capability also
exists to incorporate multiple temperature transmitting units, communicating to single
or multiple receiving units and two-way communications.
As stated earlier, the thermostat can be powered by either a long life lithium
battery for continuous operation of more than 5 years, or more preferably by a high
efficiency solar cell which charges a large memory backup capacitor. High efficiency
solar cells would provide power to the therrnostat and prevent problems associated with
dead batteries. However, because the thermostat requires light energy to charge the
capacitor, the storage capacitor may discharge if the solar cell is not exposed to
sufficient light. Therefore, a low power detection circuit is incorporated to prevent the
thermostat from transmitting during a low power situation.
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A wireless thermostat retrofit installation of thermostat is relatively simple. The
installer need only install a receiving unit at the HVAC control and program thethermostat. The operator can secure the thermostat as one would a conventional
thermostat. However, as the thermostat is now wireless, it need not be permanently
secured to the wall of the home. The operator is now able to transport the thermostat
with them to whichever room they are (;ullellLly occupying, in essence, providing an
inexpensive zone control system.
The thermostat may be further enhanced by providing an algorithm in the
HVAC controller which cycles the HVAC on and off with a predetermined duty cycle.
The battery powered thermostat is programmed to transmit at an upper and lower
temperature limit. If the predetermined duty cycle of the HVAC does not m~intz~in the
temperature within these limits, the thermostat transmits data to alter the duty cycle
accordingly. In doing this, the thermostat only fine tunes the self cycling HVACcontroller. An example of a HVAC controller operated under this principle can befound in U.S. Patent 5,248,083 and in U.S. Patent 5,307,990, both of which issued to
Adams, et al., and are hereby incorporated by reference. Further, in order to prevent the
furnace from being controlled outside normal temperatures, the HVAC controller can be
provided with a safety monitor. This safety monitor would operate to override the
temperature signals coming from the wireless thermostat in the event that the wireless
thermostat provided erroneous or no information. As an example, if the operator were
to remove the wireless thermostat from the home and place it outdoors on a cold day,
the furnace would essentially be locked in an "on" position until the override
temperature controller turned the furnace off.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a block diagram of the complete system.
Figure 2 illustrates the logic and sensing control for the thermostat.
Figure 3 illustrates the RF portion of the thermostat.
Figure 4 illustrates the RF portion of the HVAC controller.
Figure 5 illustrates the logic and control means for the HVAC controller.
Figures 6A & 6B illustrates a second embodiment of the invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 illustrates the general concept of the wireless controller. Wireless
thermostat 1 comprises general control elements 10, RF transmitter 20, and antenna 30.
General control element 10 comprises a temperature sensor for sensing ambient
5 temperature. The ambient temperature is compared to a predetermined set point by a
comparison means. The comparison means provides an error signal as a function of the
difference between the ambient temperature and the predetermined set point
temperature. RF transmitter then transmits the error signal to a control means.
Transmitter 20 may also comprise an RF receiver in the event two-way transmissions
10 are desired.
Figure 1 illustrates two possible control means which would receive data from
and possibly transmit data to thermostat 1. HVAC controller 80 represents a
conventional controller which is located on or near the temperature modifying load.
The temperature modifying load, may be a HVAC coolant or heating unit but need not
15 be so limited. For example the temperature modifying load could include means for
providing circulation of outside air into the structure or be as simple as a fan. However,
for simplification the temperature modifying load shall be referred to as the HVAC
system. HVAC controller 80 comprises antenna 32, RF receiver 85 and controller
circuitry 90. Control circuitry 90 is hardwired to the HVAC system and operates to turn
20 on and off the HVAC system. A second embodiment of the control means involves the
use of a home control system 60, such as the Honeywell Total HomeTM Control System,
or a p.c. based home control system. RF receiving unit 65 receives from and transmits
to wireless thermostat 1 through antenna 34. Control circuitry 68 and the software
incorporated therein operates to control many parameters within the home. One of these
25 parameters being the internal temperature of the home. In the second embodiment,
controller 60 would generally be hardwired to the HVAC controller 80, although home
control 60 may also transmit and receive RF signals with HVAC controller 80.
Figure 2 illustrates the logic necessary to control the timing and informationalcontent of the transmissions. Mercury switch 5 of the temperature sensing means 8
30 thermostat triggers clock/divider 11 which controls the transmitter power up, data rate,
message link and interval between messages. Temperature sensing means 8 illustrates a
simple temperature sensor, it would be simple for one of ordinary skill in the art to
CA 02224963 1997-12-16
replace temperature sensing means 8 with a programrnable setback thermostat.
Temperature sensing means 8 further provides an input to shift registers 13 and 14.
Clock/divider 11 clocks shift registers 13 &14 and bi-phase codes the 16 bits of data and
serially sends the data through data line 12 to transmitter 20. Two 4 bit words comprise
the information and 4 additional bits are used as checksum. The rem~ining bits provide
synchronization in the receiver or are unused. The 16 bit word is transmitted eight
times at three second intervals to insure reliability. Low voltage detector 15 is also
added to insure the transmitter does not lock in the transmit mode and low voltages do
not allow the solar cells to recharge the capacitor. A transmit enable is provided on line
16 when sufficient power is present to transmit.
Figure 3 illustrates the RF portion of the transmitter which contains solar power
cell 22, crystal RF oscillator 25, frequency multiplier 26 and output filter 27.Transmitter 20 is powered up for 50 ms for each tr~n~mis~ion the error signal and is
frequency shift keyed by the data in the shift register. The frequency is modulated by
modulator 24. The helical filter 29 at the output insures a clean tr~n~mi~ion of spurious
emlsslons.
Solar cell 22 and storage capacitor 23 are designed to provide power to the
wireless thermostat 1 at a constant voltage level. Though solar cell 22 and storage
capacitor 23, are shown as the power source, a long life lithium battery can be
substituted with no circuitry changes. This may be desirable in locations which have
very low light conditions over prolonged periods.
Figure 4 illustrates the analog portion of the receiver and data squaring circuit.
A crystal oscillator 81, multiplier 83 and helical filter 82 similar to that of transmitter 20
are used as the first RF oscillator which is frequency offset by 45 MHz from transmitter
20. An input helical 84 is inserted between the antenna 32 and the first mixer to
minimi7~ interference from high powered licensed transmitters. The 45 MHz I/F from
the first mixer is filtered, amplified and mixed again to 455KHz where it is filtered
again, amplified, limited and detected before being squared at the output and sent to the
receive logic. The steps are accomplished l1tili7ing second oscillator/mixer 86, second
IF filter 87 and FM amplifier/limiter/discriminator 88. The output of FM
amplifier/limiter/discrimin~tor 88 is provided to data squaring circuit 89.
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Figure 5 illustrates the logic decoder and AC power control. The CiL~;Uilly for
the data decoder is implemented in microprocessor 91 which contains logic for the data
synchronization ch~;uilly, serial to parallel conversion, checksum and word redundancy
check. The output from data squaring circuit 89 is provided to microprocessor 91. The
decoded output controls optical isolator 93 which controls triac 92. Triac 92 operates
the temperature modifying load. Power supply 94 provides power to receiver 85 and
control means 90.
In a second embodiment the majority of the components are replaced by surface
mounted integrated circuits. Figures 6A and 6B illustrate the second embodiment.Figure 6A illustrates wireless thermostat 1. Wireless thermostat 1 of the secondembodiment still utilizes temperature sensing means 8 and solar cell 22. However,
general control element 110 is a Microchip PIC 12C54. General control element 10replaces most of the discrete components of Fig. 2. The Microchip PIC 12C54 is an 8-
bit CMOS microcontroller. Transmitter 20 in the second embodiment is replaced bytransmitter 120. Transmitter 120 is a RF Monolithics, Inc. HX1000 transmitter.
Figure 6B illustrates control means 80 for the second embodiment. For the
second embodiment control means 80 is powered by a standard wall transformer 194that rectifies and steps the voltage down. Receiver 185 is a RF Monolithics, Inc.
RX1000 receiver. The received error signal is processed by control circuit 190 which is
a second Microchip PIC 12C54. The output of control circuit 190 controls triac 92
which in turn controls the temperature modifying load.
A further benefit of lltili7ing microprocessors 91 and 190 is that the system can
be set up to self cycle the temperature modifying load. By self cycling the temperature
modifying load wireless thermostat 1 need only transmit when the ambient temperature
is above or below the predetermined temperature, dependent upon the application (i.e.
heating or cooling).
It would be obvious to one of ordinary skill in the art that wireless thermostat 1
need not be limited to simple temperature sensing. One of ordinary skill in the art could
easily adapt any thermostat to communicate in the manner disclosed in the invention.
Thus allowing humidity, co2, and other commonly sensed conditions to be controlled
through wireless thermostat 1.
