Touch screen apparatus and method therefore

• US 7,250,940 B2
• Filed: 12/31/2003
• Issued: 07/31/2007
• Est. Priority Date: 12/31/2003
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Fernando, Llavanya, Jayanetti, Ruwan
• Primary Examiner(s): Awad; Amr A.
• Assistant Examiner(s): Sherman; Stephen G
• Application Number:
  US10/750,176
• Publication Number:
  US 20050140662A1
• Time in Patent Office: 1,308 Days
• Field of Search: 345173-179
• US Class Current: 345/173
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

Methods and apparatus are provided for an apparatus for inputting data. The apparatus comprises a detection circuit for providing a first reference voltage to a first and a second electrode of a first conductive layer of a resistive touch screen and providing a second reference voltage to a first and a second electrode of a second conductive layer of the resistive touch screen. The detection circuit maintains the first and second reference voltages under quiescent conditions and when the first and second conductive layers couple together. The method includes applying substantially equal voltages to the first and second electrodes of the first conductive layer of the resistive touch screen. Substantially equal voltages are applied to the first and second electrodes of the second conductive layer of the resistive touch screen. Approximately zero current is conducted in the first and second conductive layers under quiescent conditions.

Claims

1. A method of operating a resistive touch sensitive screen for increased security and lower power consumption, the resistive touch screen comprising a first conductive layer and a second conductive layer, the first conductive layer having a first electrode and a second electrode, the second conductive layer having a first electrode and a second electrode, the method comprising the steps of:

applying substantially equal voltages to the first and second electrodes of the first conductive layer;

applying substantially equal voltages to the first and second electrodes of the second conductive layer such that approximately zero current is conducted in the first and second conductive layers under quiescent conditions;

measuring currents from the first and second electrodes of the first conductive layer;

measuring currents from the first and second electrodes of the second conductive layer;

adding the currents from the first and second electrodes of the first and second conductive layers together; and

sending an alert signal when the currents from the first and second electrodes of the first and second conductive layers added together do not equal approximately zero.

2. The method of operating a resistive touch sensitive screen as recited in claim 1 further including the steps of:

touching the resistive touch sensitive screen such that the first conductive layer couples to the second conductive layer; and

determining a location where the resistive touch sensitive screen is touched using currents from the first and second electrodes of the first conductive layer and currents from the first and second electrodes of the second conductive layer.

3. The method of operating a resistive touch sensitive screen as recited in claim 2 further including a step of determining a pressure applied to the resistive touch sensitive screen using currents from the first and second electrodes of the first conductive layer and currents from the first and second electrodes of the second conductive layer.

4. An apparatus comprising:

a resistive touch screen;

a substrate;

a plurality of current to voltage converters on said substrate responsive to said resistive touch screen; and

a plurality of wires coupling said resistive touch screen to said plurality of current to voltage converters, wherein a voltage on each of said plurality of wires remains substantially constant during operation of said resistive touch screen;

an A/D converter on said substrate responsive to said plurality of current to voltage converters;

a microcontroller on said substrate responsive to said A/D converter;

wherein the resistive touch screen comprises a first conductive layer and a second conductive layer, the first conductive layer having a first electrode and a second electrode, the second conductive layer having a first electrode and a second electrode;

a detection circuit configured to measure currents from the first and second electrodes of the first conductive layer and currents from the first and second electrodes of the second conductive layer, and to add the currents from the first and second electrodes of the first and second conductive layers together; and

an alarm coupled to the detection circuit and configured to send an alert signal when the currents from the first and second electrodes of the first and second conductive layers added together do not equal approximately zero.

5. An apparatus responsive to a resistive touch screen, of the type having a first conductive layer and a second conductive layer separated from one another under a quiescent condition and coupled with each other during a touch condition, said first and second conductive layers each having a first and a second electrode, the apparatus comprising:

a detection circuit coupled to said resistive touch screen, said detection circuit configured to provide a first reference voltage to said first and second electrodes of said first conductive layer and to provide a second reference voltage to said first and second electrodes of said second conductive layer, wherein said detection circuit maintains said first and second reference voltages substantially constant during said touch condition;

wherein the detection circuit is configured to measure currents from the first and second electrodes of the first conductive layer and currents from the first and second electrodes of the second conductive layer, and to add the currents from the first and second electrodes of the first and second conductive layers together, and wherein the apparatus further comprises an alarm coupled to the detection circuit and configured to send an alert signal when the currents from the first and second electrodes of the first and second conductive layers added together do not equal approximately zero.