Touch sensing device

• US 4,567,470 A
• Filed: 04/25/1983
• Issued: 01/28/1986
• Est. Priority Date: 04/30/1982
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Yamaguchi, Hisashi, Yoshikawa, Kazuo, Asano, Toru
• Primary Examiner(s): Groody, James J.
• Application Number:
  US06/488,399
• Time in Patent Office: 1,009 Days
• Field of Search: 340/365 C, 340/365 S, 340/365 E, 340/712, 200/DIG. 1, 361/288, 361/290, 361/292, 400/479.1
• US Class Current: 341/33
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2017/9613 using two electrodes per touch switch

Abstract

A touch sensing device employing a new sensing method of the present invention is composed of the sensing portion which senses capacitance change of the touch sensing electrodes forming the touch panel, plurality of capacitance compensating capacitors which are used in common for the sensing electrodes in order to compensate fluctuation of touch sensing electrodes of the touch panel, and the ROM which is storing the data for selecting the capacitance compensating capacitors. The ON-OFF output voltage levels in the touch/non-touch conditions to the touch sensing electrodes can be equalized for each electrode and thereby the touch sensing with high accuracy can be realized by selecting the capacitance compensating capacitor by means of the ROM at the time of retrieving each touch sensing electrode.

Claims

1. In a touch sensing device comprising a plurality of sensing electrodes positioned to correspond to locations to be sensed, and a sensing circuit for sensing when a selected one of said sensing electrodes is activated, wherein said sensing circuit senses the activation of a sensing electrode by sensing a change in the electrical characteristics of said sensing electrode when said sensing electrode is activated, the improvement comprising a compensating circuit means for compensating for fluctuations in the electrical characteristics of each sensing electrode, said compensating circuit means comprising a plurality of compensating elements, wherein the number of said compensating elements is less than the number of said sensing electrodes;

memory means for storing data for selecting predetermined ones of said compensating elements for providing the compensation required for each of said sensing electrodes; and

connecting means coupled to said compensating elements and to said memory means for connecting said predetermined ones of said compensating elements to said sensing circuit, whereby the fluctuations of the electrical characteristics of said activated sensing element sensed by said sensing circuit, is compensated for.

2. A touch sensing device according to claim 1, wherein said sensing circuit comprises an oscillator, a parallel resonant circuit, tuned to the frequency of said oscillator and an impedance element connecting said oscillator to said resonant circuit, wherein said compensating circuit is connected to the connecting point of said parallel resonant circuit and impedance element.

3. A touch sensing device according to claim 1, wherein said compensating elements are capacitors.

4. A touch sensing device according to claim 3, where the unit compensating value of said sensing elements is determined with reference to the minimum compensating capacitance and the capacitance value of each capacitor is set to 2ⁿ times of the unit compensating value, respectively, where n=0, 1, 2, . . . .