Digital thermostat

A digital thermostat for automatically controlling the operation of heat transfer apparatus in which the thermostat cycles the heat transfer apparatus on and off to maintain the ambient temperature within an enclosure substantially equal to a first predetermined temperature during a first time interval and substantially equal to a second predetermined temperature during a second time interval, said thermostat comprising, in combination:

• a temperature responsive transducer for generating an analog signal proportional to the ambient temperature of the enclosure;
• converter means coupled to said transducer for generating a plurality of data signals defining a first digital data word representative of the analog temperature signal;
• an electro-optical display including a plurality of indicator elements arranged for separately indicating an alphanumeric character during a display interval;
• a plurality of driver conductors interconnecting said converter means and said electro-optical display for applying the data signals to said display elements during a display interval;
• first and second time set point data return conductors each coupled to a selected one of said display driver conductors for conducting night-to-day and day-to-night transition set point signals, respectively, in response to the application of a strobe pulse to the corresponding driver conductor;
• first and second temperature set point data return conductors each coupled to a selected one of said display driver conductors for conducting day temperature and night temperature set point signals, respectively, in response to the application of a strobe pulse to the corresponding driver conductor;
• control means coupled to said electro-optical display for periodically applying the data signals to said display during the display interval and interrupting the data signals during a scan interval following the display interval;
• a strobe generator coupled to said driver conductors for pulsing said driver conductors during said scan interval;
• a first counting circuit coupled to said time set point data return conductors for counting the number of strobe pulse return signals conducted through said time set point data return conductors during the time set point scan interval commencing with the first applicaton of a strobe pulse to a driver conductor and terminating upon the application of the Nth strobe pulse to a driver conductor, N being the number of present time resolution intervals elapsed since a predetermined reference time;
• a second counting circuit coupled to said temperature set point data return conductors and to said first counting circuit for generating a temperature set point digital data word representative of the number of strobe pulses occurring during the temperature set point scan interval commencing with the first application of a strobe pulse to a driver conductor and terminating upon the application of a strobe pulse to the driver conductor engaged in electrical contact with the day temperature data return conductor in response to a count of the first counting circuit indicating the occurrence of a night-to-day transition, or to the driver conductor engaged in electrical contact with the night temperature data return conductor in response to a count of the first counting circuit indicating the occurrence of a day-to-night transition;
• and,
• a comparator circuit coupled to said first and second counting circuits for receiving the data bits of the ambient temperature data word and the set point temperature data word, respectively, and coupled to said heat transfer apparatus for cycling said heat transfer apparatus on or off in response to a predetermined comparative relation of the ambient temperature data word relative to the set point temperature data word.

In a thermostatic control unit for use with a heating or cooling system which includes a source of operating power characterized by an alternating current waveform and a system control relay connected in series electrical relation therewith, a power divider circuit for energizing and de-energizing said system control relay in response to the presence and absence of a command signal, respectively, and for providing a continuous source of operating power for said thermostatic control unit without interfering with the operating state of said system control relay, said power divider circuit comprising:

• a semiconductor switch characterized by a holding current threshold level having a gate and a controlled conductive path through which conduction is initiated by a gate signal, sustained by forward or reverse current flow through said conductive path within said holding current threshold level and interrupted by an excursion of said alternating current waveform outside of said holding current threshold level, said conductive path having nominal anode and cathode terminals for connection in series electrical relation with said system control relay and said alternating current source;
• a power converter circuit connected in parallel electrical relation with said switch for continuously developing regulated direct current power either in response to the conduction of current from said system control relay through said converter circuit during a full cycle of the alternating current waveform or in response to the conduction of current from said system control relay through said converter circuit during only a fraction of a cycle of said alternating current waveform;
• a sync circuit coupled to said switch for generating an output pulse in response to a zero crossover of the source alternating current waveform appearing at the nominal anode terminal of said switch when said conductive path is in the open circuit condition;
• and,
• a gate control circuit coupled intermediate said sync circuit and the gate of said switch for producing a delayed gate signal in response to said sync output pulse and for conducting said delayed gate signal through the gate of said switch in response to the presence of said command signal, the conductive path being in the open circuit condition during the absence of the command signal and being in the open circuit condition during the interval commencing with the turn-off of said switch responsive to an excursion of the source current waveform outside of the holding current threshold level and terminating with the initiation of conduction in said switch in response to the application of a delayed gate signal to the gate of said switch.

In an automatic thermostat of the type having a programmable switch circuit for cycling heat transfer apparatus on and off, the improvement comprising:

• a system mode interrogator for generating a signal representative of the selected system mode;
• a temperature comparator circuit for performing the comparative relation operations (T.sub.A -T.sub.SET) or (T.sub.SET -T.sub.A) and for generating a turn-on command signal when either one of the following comparative relations is satisfied:
• T.sub.A -T.sub.SET .gtoreq.K.sub.1 in response to a mode signal indicating the cooling mode,
• T.sub.SET -T.sub.A.gtoreq.K.sbsb.2 in response to a mode signal indicating the heating mode;
• a timing circuit responsively coupled to the programmable switch and to the temperature comparator for enabling the transmission of the turn-on command signal after the elapse of a predetermined minimum-off interval following the generation of the turn-on command signal;
• and,
• a temperature differential control unit coupled to the temperature comparator to carry out the following operations in response to the presence of the turn-on command signal and to the enabling condition of the minimum-off timer:
• T.sub.A -T.sub.SET .gtoreq..DELTA.T.sub.1, in response to a mode signal indicating the heating mode, and
• T.sub.SET -T.sub.A .gtoreq..DELTA.T.sub.2, in response to a mode signal indicating the cooling mode,
• the turn-on command signal being terminated when either of the latter comparative relations are satisfied,
• wherein K.sub.1, K.sub.2, .DELTA.T.sub.1, and .DELTA.T.sub.2 are arbitrary temperature bias values, and T.sub.A =ambient temperature, T.sub.SET =set point temperature.