Claims:1. An electronic thermostat comprising:
a user interface for receiving input about target temperature from a user;
a micro-controller for receiving signal from at least one temperature sensor and for comparing the existing temperature set by user with the temperature sensed by the sensor, wherein the micro-controller generates an output based on the comparison; and
a switching circuit for receiving output from the micro-controller and adapted to control a compressor by switching according to the output given by the micro-controller, characterized in that, the switching circuit comprises at least one solid state drive switch, wherein the said solid state drive switch is a snubberless triac.

2. The electronic thermostat as claimed in claim 1, wherein the said user interface is a zone selection rotary switch or digital switch input interface having at least two operating zones.

3. The electronic thermostat as claimed in claims 1 and 2, wherein the said zone selection switch is adapted to provide defrost function at first positions.

4. The electronic thermostat as claimed in claim 1, wherein the said micro-controller is adapted to control a compressor circuit based on the desired temperature zone set by the user.

5. The electronic thermostat as claimed in claim 1 comprising a bridge rectifier in conjunction with a capacitor for providing ripple free DC output to the controlling circuit.

6. The electronic thermostat as claimed in claim 1, wherein the said at least one temperature sensor is a NTC sensor or semiconductor sensor IC, wherein the said IC is an Integrated Circuit, and further wherein the said sensor and wire harness with plugin type male/female coupler assembly can internally connect to the electronic thermostat.

7. The electronic thermostat as claimed in claim 6, wherein the said NTC sensor is configured in series with resistor and connected to the micro-controller input.

8. The electronic thermostat as claimed in claim 1 comprising a switch mode power supply or a capacitor power module, wherein the said switch mode transformer comprises one primary winding and two secondary windings for generating ripple free regulated DC voltage for noise free operations and provides isolation between high and low voltage side of switch mode power supply.

9. The electronic thermostat as claimed in claim 8, wherein the said capacitor power module works in conjunction with zener diode to give regulated DC output.

10. The electronic thermostat as claimed in claim 8, wherein the said secondary winding comprises feedback circuitry adapted for close loop generating regulated DC output.

11. The electronic thermostat as claimed in claim 1, wherein the switching circuit comprises solid state drive switch which works in conjunction with at least one optical triac drive.

12. The electronic thermostat as claimed in claim 1, wherein the said optical triac drive comprises an integrated circuit with zero-cross detector to prevent triac switch failure by ensuring triac gate fire timing event.

13. The electronic thermostat as claimed in claim 12, wherein triac switch works with the opto triac drive.

14. The electronic thermostat as claimed in claim 13, wherein the opto triac drive and the triac output switch is connected in series with a defrost heater for better switching and control of defrost function. , Description:FIELD OF THE INVENTION

[0001] The present invention relates to an electronic thermostat and its assembly. More particularly, the present invention relates to electronic thermostat control circuitry its packaging and arrangement of components.

BACKGROUND OF THE DISCLOSURE

[0002] Conventional thermostats employed in the home to control the temperature of an indoor area have generally involved the use of electromechanical devices such as spiral wound bimetallic temperature sensors which expand and contract in response to the ambient temperature of the area. The desired temperature is manually set and the system will control heating and/or cooling to maintain this desired temperature. Both heating and cooling anticipation resistors are often used to interject a known bias into the heating and cooling systems to prevent the system from overshooting the desired temperature.

[0003] These conventional systems have several disadvantages. First, only one temperature can be set in, necessitating the user's manually changing the set temperature as desired. This results in wasted energy if the system maintains the same temperature in a situation where the space in refrigerator is occupied, as compared to a situation where is the refrigerator is unoccupied or during hours when the occupants are asleep. Secondly, the system is often sensitive to small temperature fluctuations, such as those that might occur when a door is momentarily opened. This causes the system to be activated unnecessarily and more often than needed.

[0004] Electro-Mechanical thermostat refrigeration controls consist of knobs, buttons, and switches, all of which must be physically manipulated to change or activate settings. Buttons and switches either complete or interrupt a circuit to turn on an interior light or start a defrost cycle, while knobs generally use pressure or voltage to alter the target interior temperature or defrost time intervals. These controls have been used in commercial refrigeration for decades.

[0005] To make refrigeration control user friendly electrical controls in refrigeration/heating Systems were introduced. It basically comprise a simple thermostat, motor starting relay and an over load protector for controlling the motors. Larger refrigeration models also incorporate a timer and a simple logic to control an electric heater (for the automatic defrost function). Some expensive refrigeration models include one or more solenoids or motors to control blower/air flow vanes for automatic temperature control in additional compartments of the unit.

[0006] One such electronic thermostat is disclosed in the prior art document US4725001A. This prior art document discloses a “electronic thermostat” for controlling forced air heating/cooling systems and boiler-type heating systems in a manner resulting in greater fuel efficiency than has heretofore been possible. Further to employ a cycling technique in an electronic thermostat which maintains the temperature in the conditioned space precisely at set point rather than oscillating the temperature between the limits of a dead zone range.

[0007] Although the above prior art describes the about electronic thermostat in refrigeration system, the said prior arts remains silent for modular and compact electronic thermostat.

[0008] Accordingly, there is a need of electronic thermostat assembly which is easy to replace with electro-mechanical thermostat.

[0009] There is a need of electronic thermostat which serves direct replacement in place of mechanical thermostat with existing wiring arrangement.

[0010] There is a need of cost-effective electronic thermostat which is compact in design and easy to replace with electro-mechanical thermostat.

[0011] There is a need of electronic thermostat circuitry with regulated output for better switching of compressor.

SUMMARY OF THE DISCLOSURE

[0012] The general purpose of the present disclosure is to provide electronic thermostat assembly which is compact in nature and easily mountable to the refrigeration system.

[0013] To achieve the above objectives and to fulfill the identified needs, in one aspect, the present invention provides an electronic thermostat with surface mounted components.

[0014] In an aspect of the present disclosure, a user interface for receiving input about target temperature from a user, a microcontroller for receiving signal from at least one temperature sensor and for comparing the existing temperature set by user with the temperature sensed by the sensor. The microcontroller generates an output based on the comparison, and a switching signal for receiving output from the microcontroller and adapted to control a compressor by switching according to the output given by the microcontroller. The switching circuit includes at least one solid state drive triac switch, wherein the said solid state triac switch is a snubberless triac.

[0015] In an aspect of the present disclosure, the said switching circuit includes solid state drive switch which works in conjunction with at least an optical triac drive.

[0016] In an aspect of the present disclosure, the said switching circuit works without the opto triac drive.

[0017] In an aspect of the present disclosure, the said optical triac drive includes an integrated circuit with zero-cross detector to prevent triac switch failure by ensuring triac gate fire timing event.

[0018] In an aspect of the present disclosure, the said opto triac drive and the triac output switch is connected in series with a defrost heater for better switching and control of defrost function.

[0019] In an aspect of the present disclosure, the said user interface is a zone selection switch having at least two operating zones.

[0020] In another aspect of the present disclosure, the said zone selection switch is adapted to provide defrost function at first positions.

[0021] In another aspect of the present disclosure, the said zone selection switch includes rotary switch or digital switch input interface having at least two operating zones.

[0022] In an aspect of the present disclosure, the said microcontroller is adapted to control a compressor circuit based on the desired temperature value set by the user.

[0023] In another aspect of the present disclosure, the electronic thermostat includes a bridge rectifier in conjunction with a filter capacitor for providing ripple free source DC input voltage to the micro-controller and compressor drive circuit sections.

[0024] In an aspect of the present disclosure, the said at least one temperature sensor is a NTC sensor.
[0025] In another aspect of the present disclosure, the said NTC 150 sensor is configured along with divider circuit with resistor and its output is provided to micro-controller as an analog input signal.

[0026] In an aspect of the present disclosure, the said optical triac drive 130 includes an integrated circuit with zero-cross detector to prevent triac switch failure by ensuring triac gate fire timing.

[0027] In an aspect of the present disclosure, the electronic thermostat includes a through hole / surface mountable switch mode transformer or a capacitor power module. The switch mode transformer consist three numbers of windings. The three numbers of windings includes one high voltage switching winding and one bias winding at primary side and one winding at secondary side for generating a high voltage isolated and ripple free regulated source dc voltage to control circuit sections.

[0028] In another aspect of the present disclosure, the said capacitor power module works in conjunction with zener diode for generating regulated DC output.

[0029] This together with the other aspects of the present invention along with the various features of novelty that characterized the present disclosure is pointed out with particularity in claims annexed hereto and forms a part of the present invention. For better understanding of the present disclosure, its operating advantages, and the specified objective attained by its uses, reference should be made to the accompanying descriptive matter in which there are illustrated exemplary embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The advantages and features of the present disclosure will become better understood with reference to the following detailed description and claims taken in conjunction with the accompanying drawing, in which:

[0031] Fig. 1 illustrates a block diagram of an electronic thermostat, in accordance with certain exemplary embodiments of the present invention;

[0032] Fig. 2 illustrates an isometric view of electronic thermostat control circuit assembly with both printed circuit boards interfacing arrangement, in according to various embodiments of the present invention;

[0033] Fig. 3 illustrates a bottom view of the electronic thermostat, according to various embodiments of the present invention;

[0034] Fig. 4 illustrates a circuit diagram of AC to DC section of the first printed circuit board according to various embodiments of the present invention;

[0035] Fig. 5 illustrates a circuit diagram of the Micro-Controller board, according to various embodiments of the present invention;

[0036] Fig. 6 illustrates a zone selection switch, according to various embodiments of the present invention;

[0037] Fig. 7 illustrates a data sheet recommended reset circuit diagram;

[0038] Fig. 8 illustrates a circuit diagram of thermostat triac output section;

[0039] Fig. 9 illustrates an interfacing port detailed circuit diagram of first printed circuit board and second printed circuit board;

[0040] Fig. 10 illustrates the measurement of the electronic thermostat; and

[0041] Figs. 11-24 illustrate the block diagrams and the circuit diagrams of variants of the electronic thermostat, in accordance with various embodiments of the present invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0042] The foregoing descriptions of specific embodiments of the present disclosure have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiment was chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0043] The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0044] The terms “having”, “comprising”, “including”, and variations thereof signify the presence of a component.

[0045] The present invention relates to an electronic thermostat, and its circuitry. The said electronic thermostat shall now be explained in conjunction with Figs. 1-24.

[0046] Referring to Figs. 1-3, there is shown a block diagram of an electronic thermostat 100 in Fig. 1, and the layouts and its assembly in Figs. 2-3. The shown electronic thermostat 100 includes a microcontroller 110, a user switch input interface 160, an opto triac drive 130, an externally connected temperature sensor 150, an ac-dc module 170, and a triac output switch 180.

[0047] Further, the NTC 150 sensor may include wire harness with plugin type male/female coupler assembly or wire soldered type which can connect internally to the electronic thermostat 100.

[0048] It will be apparent to a person skilled in the art that usually both types of temperature sensors, such as positive temperature coefficient or negative temperature coefficient sensor, are used in conventional refrigeration systems.

[0049] However, in the present invention, the temperature sensor 150 is of negative temperature coefficient type and is used to sense the temperature of target place on evaporator of a refrigeration system.

[0050] In an embodiment, the said negative temperature coefficient sensor 150 includes resistors whose resistance decreases with increase in temperature. Such NTC resistors are usually fabricated from platinum, nickel, cobalt, iron and silicon. However, other materials could also be used.

[0051] In an embodiment, sensor is configured along with divider circuit with resistor R7 (550) and its output is provided to micro-controller as an analog input signal.

[0052] In an embodiment of the invention, the electronic thermostat circuitry 100 includes the micro-controller 110. The micro-controller 110 includes a 12 bit / 14 bit / 16 bit analog to digital module. The 12 bit / 14 bit / 16 bit analog to digital module of the micro-controller is fast and accurate and helps to improve temperature measurement accuracy of the said temperature sensor 150.

[0053] Further, NTC sensor 150 is configured with potential divider circuit connected to microcontroller, which increases the measurement accuracy of temperature within range of +/- 0.5?.

[0054] The micro-controller 110 further includes EEPROM memory reprogrammable for logical instruction. The logical instruction of temperature preference can be set by user or set by manufacturer of the refrigeration system. The EEPROM memory data memory can be re-programmed several times and data retention is usually more than 10 years.

[0055] In an embodiment of the invention, 8/10 pin micro-controller 110 is used for controlling functional logic. The said Micro-controller 110 is a 8 bit core and includes an inbuilt 12 bit analog to digital module, which used here for better temperature measurement accuracy.

[0056] Going further, the opto triac drive 130 provides isolation between low power and high power switching circuit of the electronic thermostat 100.

[0057] Moreover, isolation between low power and high power switching circuit meets standard safety norms and provides safety to the user and the refrigeration system.

[0058] In an embodiment, the opto triac drive 130 is used with zero-cross detector to prevent triac output switch 180 failure by ensuring triac gate fire timing, which improves on-off switching cycle life of the triac output switch 180. In an embodiment, the said optic triac drive 130 includes an inbuilt zero-cross detector module, which prevents from early failure issues of triac switch due to mis-firing of gate.

[0059] In an embodiment of the invention, the opto traic drive 130 gives switching instruction to the triac output switch 180. The triac output switch 180 in turn makes compressor 140 of the refrigeration system on or off, thereby controlling the temperature in the refrigeration system.

[0060] In an embodiment, the electronic thermostat 100 circuitry is made on two printed circuit boards, as shown in Figs. 2-3. The first printed circuit board 105 includes the ac-dc module 170 and the triac output switch180. The second printed circuit board 120 includes the microcontroller 110, the user interface 160 and the opto triac drive 130.

[0061] Referring to Fig. 2, the user interface 110 includes a zone selection switch 210 which is part of the second printed circuit board 120. In an embodiment, the zone selection switch 210 with rotary arrangement includes four positions. The rotary switch position one is used for defrost function, the remaining three rotary switch position is used for different zone selection e.g. zone 1 to zone 3. The zone selection switch 210 is better shown in Fig. 6 and explained below.

[0062] In an embodiment, the second printed circuit board 120 is connected with the first printed circuit board 105 at a connecting port 560 & 570.

[0063] In an embodiment, the first printed circuit board 105 includes an electrolytic capacitor 240, power terminals 270, a varistor 260, a switch mode transformer 230 and the triac output switch 180 & 430(Q2).

[0064] In an embodiment, electrolytic capacitor 240 is used in circuitry to smoothen the DC high voltage supply by filteration, which generates from AC voltages in conjunction with the (Bridge rectifire module) 400, (Fusible power resistor) 410 and varistor 260. The bridge rectifier 400 is used for AC to DC voltage rectification work. Fusible power resistor 410 is used in circuit as safety device which fused in case of excess current drain by whole circuit and protect other used components from damage. The varistor 260 is adapted to work against voltage surges and spikes, such as those generated by inductive switching and mains line transients.

[0065] In an embodiment, the switch mode transformer 230 is used for converting DC high voltage (350V) to DC low voltage (5V) with the help of high frequency switching technique between primary sides of winding using AC to DC controller 390. Hence, close loop regulation of output voltage is done by bias winding input at the feedback pin. This switching of the internal power MOSFET is controlled by this feedback pin, wherein feedback pin senses voltage from bias winding of transformer.

[0066] As shown in Fig. 3, the electronic thermostat 100 with zone selection switch 210 is electrically connected with second printed circuit board 120. The second printed circuit board 120 is mating with the first printed circuit board 105 at slot 330.

[0067] In an embodiment, the first printed circuit board 105 includes an AC-DC controller IC 390 and an output port 380 which is connected to the compressor 140 of the refrigeration system, a phase port 370 and a neutral port 360 connected to the main ac supply. Further, the AC-DC IC 390 have energy efficient regulation feature with RoHS compliant package.

[0068] In an embodiment, the first printed circuit board 105 also includes a surface mountable capacitor 350 which plays role of an externally provided filter device for IC 390 internal 6V regulator supply, a surface mountable resistor 340 & 440 set as divider circuit in parallel of bias winding of transformer 230, and output of this divider circuit is directly connected to AC to DC controller ic 390 at pin no 2. This connectivity creates a close loop controlling of secondary output voltage and a slot 330 is provided for interfacing first and second printed circuit boards 105, 120 with help of soldering.

[0069] Coming to Fig. 4, the schematic circuit diagram of the first printed circuit board 105 is shown. As show in this Fig. 4, the switch mode transformer 230 has one primary winding with tapping 3 and 4 respectively, and two secondary windings with tapping 1, 2 and 5, 6.

[0070] Further, the secondary winding with tapping 5 and 6 is the output terminal for regulated DC voltage. The secondary winding with tapping 1 and 2 is provided as a bias winding.

[0071] In an embodiment, the said bias winding is connected to U1 (390) feedback pin with help of resistors R3 (440) and R4 (340) divider point.

[0072] In an embodiment, the bias winding is connected to U1 driver circuit 390. The U1 driver circuit 390 includes MOSFET as a switch, which provides input power to the switch mode transformer 230 according to difference in the output side of the switch mode transformer 230.

[0073] In an embodiment, diode D1 (480) is provided on the secondary side of the switch mode transformer 230. The diode D1 (480) act as rectifier and converts high frequency sinusoidal AC into direct current (DC). In an embodiment, capacitor C2 (X10) is provided as a smoothing capacitor to generate ripple free DC source voltage for micro-controller and control sections.

[0074] Now referring to Fig. 5, the second printed circuit board 120 circuitry is illustrated. The second printed circuit board 120 includes the 8 bit micro-controller 110. The micro-controller 110 includes ten pin in which four pins 2 to 5 is connected to the zone selection switch 210. The pin 6 and 7 is connected to the opto triac switching devices 510, 520 through resistor R9 (540) and R10 (500).

[0075] In an embodiment, a defrost switch indicator 530 is connected to the microcontroller 110 at 9 no pin through a current limiting resistor R8 (490).

[0076] Now referring to Fig. 6, it provides zone selection rotary switch 210 with four rotary positions for selecting different zone. In an embodiment, if refrigerator is running in cold zone and user wants to put in defrost mode then user have to change position of rotary switch to defrost position for ?5 second.

[0077] In an embodiment, once the 5 second is completed the micro controller 110 will put on 3 mm LED light D8 (530) indicating as acceptance of defrost command to the user. In an embodiment, user can set rotary switch zone position to other zone after keeping the switch in defrost position for ?5 second.

[0078] In an embodiment, four zone selection options include hot zone, cold zone, normal zone and defrost zone.

[0079] In an embodiment, the rotary zone selection switch 210 includes defrost zone, warm zone, normal zone and cold zone.

[0080] In an embodiment, the zone selection switch could be dome type push button switch and various printed circuit board indicators are present thereon for user convenience.

[0081] As shown in fig. 7, standard reset circuitry (590) is used as per the standard micro-controller datasheet recommendation.

[0082] As shown in fig. 8, the triac output switch 180 is used for compressor side switching with defined triac gate current limiter resistor (R5) 450, and in similar way (Q2) 430 is used for heater side switching along with (R6) 460. This provided provision on printed circuit board by considering auto defrost thermostat hardware requirement only, so that same hardware can be utilized with firmware changes.

[0083] As shown in fig. 9, resistor (R7) 550 is used in NTC divider circuit at VCC side. A pads output port (P2-F) 560 of first printed circuit board with seven signal line which is used to interfacing with output port (P2-M) 570 of the second printed circuit board 120 with same signal sequence. A port P3 is used for connectivity of NTC sensor to the thermostat.

[0084] As shown in fig. 10 dimensions of electronic thermostat and its components have been shown. The electronic thermostat 100 having length within the range of from about 55 mm. to about 65 mm. Further, width of the electronic thermostat 100 is within the range of from 25 mm to about 35 mm.

[0085] In use, the electronic thermostat 100 works as follows. At first, the sensor 150 of the refrigeration system detects the temperature of the evaporator compartments of the refrigeration system. Thereafter, the user may set a predefined temperature required to be maintained through the user interface 210.

[0086] If the temperature of the compartment of the refrigeration system is more or less of the predetermined value set by user, the electronic thermostat 100 begins operation. More specifically, the micro-controller 110 of the thermostat 100 after comparing the difference in temperature, switches the switching circuit of the triac output 180 ON/OFF for the required time till temperature inside the compartments reaches the value set by user.

[0087] In an embodiment, the user can select different temperature zone as provided by the zone selection switch 210. If user selects cold zone, temperature range for the cold zone is selected. The micro controller 110 then compares the temperature of the evaporator and temperature set by user. The difference of the temperature calculated by the micro-controller 110 switches the opto triac drive 130 and triac output switch 180. The opto triac drives 130 and triac output switch 180 switch the compressor 140 ON of the refrigeration system for the particular time period until evaporator temperature of the refrigeration system reaches determined value set by user. In this manner, the electronic thermostat 100 is able to control the temperature of the refrigeration system.

[0088] In an embodiment, the some of electronic components used in the electronic thermostat 100 are surface mountable components. The use of surface mountable components makes electronic thermostat 100 compact.

[0089] Further, the use of transformer 230 and U1 SMPS driver circuit 390 in the electronic thermostat 100 makes it small in size, also as better regulated output is achieved with less number of electronic components.

[0090] Moreover, due to surface mountable components and its fabrication on the two printed circuits board and smart arrangements of electronic components makes electronic thermostat more accurate, economical and small in size.

[0091] Further, figs.11-24 illustrates variants of the electronic thermostat 100 in form of block diagrams and their respective circuit diagrams. The variants of the electronic thermostat 100 with modified components are described below: -

Variants/Fig. No. Component added or changed Components detail
Variant-1/ Fig. No. 11 and 18 Capacitor power module 172 is used in place of ac-dc module 170.

Opto triac drive 130 is removed. Used capacitor power module 172 in place of ac-dc module 170.

Further, Zener diode 443 is used in conjunction with capacitor power module 172 to generate a regulated DC output. The Zener diode is used to generate a fixed voltage by passing a limited current through using the series resistor R4 340. The Zener output voltage is not seriously affected by resistance and the output remains as a stable reference voltage.
Rotary Switch used for the temperature zone selection and the defrost mode.
Variant-2/ Fig. No. 12 and 19 Opto triac drive 130A, triac output switch 180A and digital switch input interface 160 A are added. Opto triac drive 130A and traic output switch 180A are added in series with defrost heater 111 for better switching and timing control of defrost operation in refrigeration circuit.

Further, user digital switch input interface 160 A is added in place of rotary switch input 160.
Variant-3/ Fig. No. 13 and 20 Capacitor power module 172 is used in place of ac-dc module 170.

Opto triac drive 130 is removed. Used capacitor power module 172 in place of ac-dc module 170.

Further, Zener diode 443 is used to generate a regulated DC output. The Zener diode is used to generate a fixed voltage by passing a limited current through it using the series resistor R4 340. The Zener output voltage is not seriously affected by resistance and the output remains as a stable reference voltage.
Rotary Switch is used for temperature zone selection & Defrost Heater timing control added.
Variant-4/ Fig. No. 14 and 21 Digital switch input interface 160 A is used in place of rotary switch input interface 160. Digital switch input interface 160 A is added in place of rotary switch input 160.

Further, PCB dome switch is used with smd led indications for zone selection.
AC-DC module is used to regulate DC supply for micro-controller and controlling circuitry.
Variant-5/ Fig. No. 15 and 22 Digital switch input interface 160 A is used in place of rotary switch input interface 160. Digital switch input interface 160 A is added in place of rotary switch input 160.

Further, PCB dome switch is used with smd led indications for zone selection.

Furthermore, capacitor Power module 172 is used in place of AC/DC module 170. Zener diode 443 is used to give regulated DC output. The Zener diode is used to fix voltage by passing a limited current through it using the series resistor R4 340.
Variant-6/ Fig. No. 16 and 23 Opto triac drive 130A, triac output switch 180A and digital switch input interface 160A is added. Opto triac drive 130A and triac output switch 180A is added in series with defrost heater 111 for better switching and control of defrost operation.

Further, user digital switch input interface 160A is added in place of rotary switch input 160.
AC-DC module is used to regulate DC supply for micro-controller and controlling circuitry.
Variant-7/ Fig. No. 17 and 24 Triac output switch 180A, defrost heater 111 and digital switch input interface 160A is added.

Capacitor power module 172 is used in place of ac-dc module 170.
Used capacitor power module 172 in place of ac-dc module 170. Digital switch input interface 160 A is added in place of rotary switch input 160.

Further, PCB dome switch is used with smd led indications for zone selection and capacitor power module 172 is used to generate a regulated DC output.
Defrost Heater timing control added.

[0092] The present electronic thermostat is unique and novel. The present electronic thermostat is capable of providing compact and easy to replace design with electro-mechanical thermostat. The present electronic thermostat circuitry capable of providing regulated output for better switching of compressor.

[0093] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the scope of the present invention.