Abstract: A microcomputer controlled digital thermostat is powered by supply voltage derived from a large capacitance (e.g. 3.3 farad) voltage supply capacitor. The voltage supply capacitor is normally charged by an AC voltage which is derived from the furnace and which is rectified by a full wave rectifier bridge. Time and temperature data are stored in read/write RAM storage. The microcomputer controls operation of the thermostat as a function of sensed temperature and the stored time and temperature data. A voltage sensing circuit senses the supply voltage from the voltage supply capacitor and prevents the supply voltage from being provided to the microcomputer and other portions of the thermostat control circuitry when a prolonged interruption of AC power causes the supply voltage to decrease to a predetermined value. The supply voltage continues to be supplied to the read/write RAM to retain the stored time and temperature data.

Abstract: A microcomputer controlled digital thermostat has separate, independent registers for storing heating control information and cooling control information. On a periodic basis, the microcomputer determines whether the furnace should be turned on, based upon a temperature signal indicative of room temperature, a time-of-day value indicative of the present time of day, and the stored heating control information. If the furnace is already off and the microcomputer determines that it should remain off, the microcomputer then determines whether air conditioning is needed, based upon the temperature signal, the time-of-day value, and the stored cooling control information.

Abstract: A microcomputer controlled digital thermostat has a two-digit display which normally displays room temperature and a plurality of function and temperature keys for storing control information in the microcomputer. The function keys include a TIME SET key, a HEAT SET key, an AC SET key, and an AC OFF key. The temperature keys include keys for each of a plurality of temperature ranges such as 59.degree.-59.degree. F., 60.degree.-69.degree. F., and 80.degree.-89.degree. F. Time and temperature settings are entered and stored in registers of the microcomputer by a slew entry arrangement through use of the function keys and temperature keys, together with the display. Recall of the stored settings is provided by rapidly contacting the function keys.