Electrostatic input device

An electrostatic input device comprising:

• a plurality of electrostatic sensor electrodes;
• a measurement circuit configured to output a plurality of measurement values based on a capacitance between each of the plurality of electrostatic sensor electrodes and an indication body at a predetermined interval;
• a processor configured to determine, based on the plurality of measurement values, a proximity state in which the indication body is in proximity to the plurality of electrostatic sensor electrodes;
• and
• a memory configured to store, as a reference value, a predetermined measurement value output from the measurement circuit, the reference value corresponding to a non-proximity state in which the indication body is not in proximity to the plurality of electrostatic sensor electrodes,
• wherein the processor is further configured to:
• determine the proximity state based on a plurality of first difference values obtained by subtracting the reference value from, each of the plurality of measurement values;
• calculate a plurality of sum difference values obtained by summing up the plurality of first difference values at the predetermined interval;
• determine, in the proximity state, a first state in which a current sum difference value of the plurality of sum difference values decreases more than a first previous sum difference value of the plurality of sum difference values;
• determine, in the proximity state, whether a fluctuation amount of the plurality of sum difference values is smaller than a predetermined value after the processor determines that the current sum difference value decreases more than the first previous sum difference value;
• determine, in the proximity state, whether a second state, in which the fluctuation amount of the plurality of sum difference values is smaller than the predetermined value, continues for a predetermined time or more;
• update the reference value to an updated reference value under conditions below:
• the processor determines, in the proximity state, the first state at a first time;
• and
• the processor determines that the second state continues for the predetermined time or more from the first time;
• and
• determine the proximity state based on a plurality of second difference values obtained by subtracting the updated reference value from each of the plurality of measurement values.