Patent ID: 8602744

Claim:
A capacitance sensor system configured to be used in a liquid pumping system, the liquid pumping system comprising a liquid reservoir and an impeller pump located inside the reservoir to pump liquid out of the reservoir, wherein the capacitance sensor system comprises: a. a capacitance sensor within the reservoir for contact with the liquid and having a capacitance value that depends on contact between the liquid and the capacitance sensor; and b. a control module having a microcontroller comprising: i. a feedback output connected through a feedback resistor to an input of the microcontroller and to the capacitance sensor; ii. a first timing counter that starts when the microcontroller sets the feedback output of the microcontroller to a predetermined high state value and stops when the input of the microcontroller reaches the predetermined high state value, the first timing counter of the microcontroller thereby determines a first time required for the feedback output to raise the input of the microcontroller connected to the capacitance sensor to the predetermined high state value; iii. a second timing counter that starts when the microcontroller sets the feedback output to a predetermined low state value and stops when the input of the microcontroller reaches the predetermined low state value, the second timing counter of the microcontroller thereby determines a second time required for the feedback output to lower the input of the microcontroller connected to the capacitance sensor to the predetermined low state value; and iv. a comparator for comparing the combined first time and second time to a predetermined threshold to determine if the liquid in the reservoir is in contact with the capacitance sensor.