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Capacitive Touchscreen Enhancement

IP.com Disclosure Number: IPCOM000036550D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Powell, KE: AUTHOR [+2]

Abstract

This article describes a circuit arrangement for capacitive touchscreen enhancement which eliminates position errors encountered by various random users.

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Capacitive Touchscreen Enhancement

This article describes a circuit arrangement for capacitive touchscreen enhancement which eliminates position errors encountered by various random users.

In the existing art of capacitive touchscreen technology, the touch location is found by measuring the current being drawn by the user as the conductive surface of the screen is contacted. This current is calculated by a microcomputer or like device and the position of the touch is determined. A typical circuit to accomplish this is depicted in Fig. 1. In this article only one plane of the touchscreen is illustrated. It is understood that in actual applications two planes would be activated, often by switching the circuitry from one plane to the other via electronic switching. In Fig. 1, and oscillator 5 generates a signal which is applied to points A and B. Resistors 2 and 3 are of equal value and there is no current flow through the touchscreen surface 1. When the conductive surface 1 is touched, the circuit is modified by the impedance of the user touch 4 and current will flow through the touchscreen surface 1 from both points A and B. The current from point A varies the voltage drop across resistor 2 and this condition varies at the rate of the oscillator 5. The signal at point A is amplified by amplifier 6, converted to digital by A/D converter 7 and applied to a microcomputer 8 for determination of the touch position.

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In looking at the circuit of Fig. 1 it would appear that if the impedanc...