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Abstract

The present invention performs analog to digital conversion using the system clock of a microprocessor, the system clock being the clock which controls the rate of operation of the microprocessor. A varying analog signal is applied to the clock frequency control input of the microprocessor, thereby causing the clock frequency and the rate of operation of the microprocessor to vary in accordance with the varying analog signal. The clock is counted for a predetermined period of time. In the preferred embodiment this predetermined period of time is set by the 60 Hz AC power line. The counted contents at the end of this predetermined period of time is a digital representation of the varying analog signal. The microprocessor includes circuits for performing other operations at the rate set by the clock frequency. The other operations performed by the microprocessor must not be deleteriously affected by the varying rate of operation caused by the varying analog signal. In the preferred embodiment the varying analog signal is the output of a thermistor corresponding to the ambient temperature and the microprocessor includes additional control functions for using the digital representation of the analog signal for thermostatic control of a temperature modifying apparatus.

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First Claim