Patent ID: 7472028

Claim:
An apparatus for measuring a parameter, the apparatus comprising: a microprocessor having a plurality of pins; a sensor capacitor configured to change capacitance as the parameter changes, the sensor capacitor having a first lead electrically connected to a first pin of the microprocessor, and a second lead electrically connected to a second pin of the microprocessor; a first reference capacitor having a first lead electrically connected to a third pin of the microprocessor, and a second lead electrically connected to the second pin of the microprocessor; a resistor having a first lead electrically connected to a fourth pin of the microprocessor, and a second lead electrically connected to the second pin of the microprocessor; a second reference capacitor having a first lead electrically connected to a fifth pin of the microprocessor, and a second lead electrically connected to the second pin of the microprocessor a comparator configured to detect whether a threshold voltage has been reached; a timer, wherein the apparatus is configured to use the timer to measure how long it takes for: the sensor capacitor to reach the threshold voltage; the first reference capacitor to reach the threshold voltage; and the second reference capacitor to reach the threshold voltage; wherein the sensor capacitance is calculated using the formula: Sensor Capacitance=[(TimerS−Timer1)/(Timer2−Timer1)](Ref2−Ref1)+Ref1 wherein: TimerS is the time for the sensor capacitor to reach the threshold voltage, Timer 1 is the time for the first reference capacitor to reach the threshold voltage, Timer 2 is the time for the second reference capacitor to reach the threshold voltage, Ref 1 is the capacitance of the first reference capacitor, and Ref 2 is the capacitance of the second reference capacitor.