An apparatus, system, and method for measuring parameters, measuring or determining capacitance, producing a digital output that is dependent upon a capacitance, or converting a variable capacitance output, of a sensor capacitor for example, into a digital format. By activating and deactivating pins, a microprocessor may form various circuits, for instance, each containing a resistor and a different capacitor and, in some embodiments, without the use of intermediate switching components. The microprocessor may alternately measure the time to change the charge of each of the capacitors and then calculate the capacitance of one of the capacitors using the measured times and known capacitances of one or more reference capacitors. Certain embodiments use two reference capacitors and alternately charge and discharge the capacitors, and a simple formula may be used to calculate capacitance using times to reach a threshold voltage. A measured parameter may be humidity or pressure, for example.
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to, and the benefit of, U.S. Provisional Application Ser. No. 60/583,159 filed Jun. 25, 2004, and entitled "Sensor Interface Circuit", which is hereby incorporated by reference.
