Patent ID: 8217666

Claim:
A capacitance detection apparatus comprising: a first switch disposed between opposed terminals of a reference capacitance, one of the opposed terminals of the reference capacitance being connected to a first potential source; a second switch disposed between the other terminal of a measured capacitance and the other terminal of said reference capacitance, one terminal of terminal of said measured capacitance being connected to a second potential source or a free space; a third switch disposed between the opposed terminals of said measured capacitance; a first switch operation rendering said first switch to a closed state and then returning said first switch to an opened state upon lapse of an initialization period, a second switch operation rendering said second switch to a closed state and then returning said second switch to an opened state upon lapse of a first charging period, a third switch operation rendering said third switch to a closed state and then returning said third switch to an opened state upon lapse of a first discharging period; a first switching control process executing said second switch operation and said third switch operation alternately after executing said first switch operation; a second switching control process executing said first switch operation and then executing said second switch operation for a second charging period different from said first charging period and executing said third switch operation for a second discharging period, in alternation; a switch controlling unit for alternately executing the first switching control process and the second switching control process; a potential determining unit for determining whether the potential of the other terminal of said reference capacitance has changed to a predetermined set potential from an initial potential after said first switch operation, by said first switching control process and said second switching control process; a counting unit for counting the number of times of repetition of said second switch operation executed until the potential of the other terminal of the reference capacitance changes to said set potential, in said first switching control process and said second switching control process; and an output determining unit for determining presence/absence of change in capacitance of said measured capacitance, based upon the counted number of repetition times counted in at least one of said first switching control process and said second switching control process, said output determining unit determining also whether the change in the capacitance in the measured capacitance is due to an event of detection interest or not, based on the numbers of repetition times in said first switching control process and the number of repetition times in said second switching control process.