Position measurement apparatus for capacitive touch panel system

Details Position measurement apparatus for capacitive touch panel system Position measurement apparatus for capacitive touch panel system

1988-06-13

1989-08-01

Schreyer, Stafford D.

Telegraphy

Systems

Position coordinate determination for writing

340706, G08C 2100

Patent

active

048534986

ABSTRACT:
A capacitive touch panel system (10) having a faceplate (14) with an electrically conductive layer (20) of a consistent resistivity employs a position measurement apparatus (12) to generate an address signal indicative of a position (46) on the faceplate in contact with a stylus (48). The position measurement apparatus includes a position measurement signal source (62) that generates a square-wave measurement signal of substantially constant frequency and a preselected magnitude. The position measurement signal is applied to a first pair of opposed electrodes (36) and (40) and a second pair of opposed electrodes (38) and (42) positioned along respective side margins (26, 30, 28, and 32) of the faceplate. The resistivity of the conductive layer establishes effective resistances of R.sub.x and R.sub.y between the respective first and second pairs of electrodes. Position measurement subcircuits (60a-60d) measure currents drawn through the electrodes whenever the stylus contacts the conductive layer, thereby to form an address signal indicative of the location at which the stylus contacts the faceplate.

REFERENCES:
patent: 4476463 (1984-10-01), Ng et al.
patent: 4707845 (1987-11-01), Krein et al.
Panttaja, "Touch screens let your fingers provide a fast, simple entry into the computer," Electronics, Apr. 19, 1984, 140-144.

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