Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2000-05-01
2001-10-23
Tong, Nina (Department: 2632)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S315000, C340S653000, C318S672000
Reexamination Certificate
active
06307464
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to heating and cooling systems for buildings and the like and more particularly to thermostat circuits used with a microcontroller based controller for such systems.
BACKGROUND OF THE INVENTION
In present residential HVAC (heating, ventilating and air conditioning) systems a 24 volt AC signal is sent from a wall thermostat to a receiving control. The control either reads the signal as ON or the signal is used to directly turn on a 24 VAC electromechanical device. The signal is read as ON or OFF depending on the presence of the 24 VAC with respect to ground. For each function added, e.g., each electromechanical device added, typically at least one new wire is provided.
SUMMARY OF THE INVENTION
It is an object of the present invention to add functions while minimizing the wires needed. Another object is the provision of a control in which functions are added without adding wires.
Briefly described, the invention uses the same 24 VAC signal and substantially the same wiring as in conventional controls but reads the signal in a different way. A receiving control is employed using a full wave power supply which provides a logic ground which is different from earth ground in the 24 VAC control. The logic ground is at a different potential from earth ground (24 VAC ground) and is a different potential from 24 VAC. The invention takes advantage of the ability to read the 24 VAC signal as potentially four different states by using a microcontroller.
Since the voltages are compatible with 24 VAC and 24 VDC components, the circuit on this line is capable of driving these loads as well as reading the status of switches. Extra wiring is avoided by using one wire in a dual function, i.e., as both an input as well as an output. The phasing and the circuit is used so that when a switch is pressed, the microcontroller uses a line normally used as an output as an input. In the preferred embodiment, this is used in a diagnostic circuit to alert a user of the HVAC unit of system problems with a blinking light and/or an audible alarm. The indicator light and alarm can be mounted near the thermostat or on the HVAC unit, as desired.
Additional objects and features of the invention will be set forth in part in the description which follows and in part will be obvious from the description. The objects and advantages of the invention may be realized by means of the methods, means of instrumentalities and combinations, particularly pointed out in the appended claims.
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patent: 5604424 (1997-02-01), Shuttleworth
patent: 6236552 (2001-05-01), Hattori
Anderson Timothy L.
Garnett Ronald E.
Miller Mark E.
Baumann Russell E.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Tong Nina
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