Abstract: The present invention is a method and apparatus for determining the exterior ambient temperature in a heat pump. In accordance with the prior art the heat pump defrosts the exterior heat exchanger if the exterior heat exchanger temperature has a predetermined relationship to the exterior ambient temperature. The exterior heat exchanger temperature is measured directly via a temperature sensor. The improvement of the present invention includes operating the exterior fan after operation of the compressor, while repetitively measuring the temperature of the exterior heat exchanger until reaching a plateau temperature other than freezing. The exterior ambient temperature is set to the plateau temperature. In the event that the plateau temperature equals freezing, the exterior ambient temperature is set equal to a compromise temperature slightly above freezing, preferably 34 degrees Fahrenheit.

Abstract: The present invention is a technique for forming a signal representing the operator adjustment of a potentiometer. This technique consists of measuring the reference time constant of the resistance between the fixed terminals of the potentiometer and a capacitor, measuring the variable time constant of the resistance of potentiometer between a fixed terminal and the terminal variable by an operator setting and this same capacitor, and again measuring the reference time constant of the resistance between the fixed terminals of the potentiometer and the capacitor. These time constant measurements are made by discharging the capacitor, charging the capacitor through the appropriate terminal of the potentiometer and measuring the time required for the voltage across the capacitor to reach a predetermined threshold level. This measurement sequence is repeated if the two measures of the reference time constant differ by more than a predetermined amount.

Abstract: The present invention is a technique for forming a digital signal representing an environmental condition. The technique consists of measuring the variable time constant of an analog sensing device having a variable resistance dependent upon the environmental condition and a capacitor as well as measuring the reference time constant of a precision fixed resistor and the same capacitor. The time constants are measured by discharging the capacitor, charging the capacitor through the appropriate element and measuring the time for the voltage across the capacitor to reach a predetermined level. Lastly, the digital ratio between the two time constants is formed. This digital ratio is the digital representation of the environmental condition sensed by said analog sensing device.

Abstract: The present invention is a technique for operator entry of a time program into a programmable device. An operator adjustable input device having associated time indicia is employed to enter a time signal indicative of a time a selected time. A manual control state input device enables selection of one a control state. When the programmable device is in a program mode the selected control state is stored in a program memory at a location corresponding to the selected time. This program memory stores a program of control states for particular times. When in a control mode a clock signal indicative of the current time permits recall of the control state for the current time, thus permitting control in accordance with the recalled control state. In accordance with the preferred embodiment the programmable device is an electronic thermostat.

Abstract: The present invention is a method for specifying a constant in a digital electronic system. This technique employs the ratio of resistances between a reference resistor and a constant specifying resistor. The time constant of the constant specifying resistor and a capacitor is measured by discharging the capacitor, charging the capacitor through the constant specifying resistor and counting the number of predetermined time intervals required for the voltage across the capacitor to reach a predetermined threshold voltage. A similar time constant measurement is made for the reference resistor and the capacitor. The same conditions are employed as far as possible during these two measurements to insure the only differences are in the value of the resistances. The externally specified constant is computed from the digital ratio of the time constant of the constant specifying resistor and the time constant of the reference resistor.

Abstract: The present invention is a technique for thermostatic control of a temperature modifying apparatus such as a heating unit or an air conditioning unit. This technique involves measuring the ambient temperature, generating an error signal based upon the difference between a set point temperature and the measured ambient temperature, operating the temperature modifying apparatus according to the error signal, and adjusting the set point temperature based upon the time history of the error signal. In accordance with the preferred embodiment of the present invention, the temperature modifying apparatus is operated during the next cycle interval with a duty cycle proportional to the error signal at the start of the cycle interval.

Abstract: The present invention is an electronic thermostat having correction for the self heating due to the semiconductor switching device used to switch a temperature modifying apparatus on. This invention includes a semiconductor power switching device disposed on an upper portion of a vertically oriented circuit board, a first thermistor disposed on the circuit board at a lower portion thereof remote from the semiconductor power switching device, and a second thermistor disposed on the circuit board at a portion intermediate between the semiconductor power switching device and the first thermistor. A corrected ambient temperature is generated from the temperature indicated by the first thermistor and the difference in indicated temperature between the second thermistor and the first thermistor. The state of the semiconductor power switching device is then controlled based upon the relationship between the corrected temperature and a desired temperature.