Infrared touch input device and light emitted activation circuit

• US 5,055,840 A
• Filed: 11/01/1990
• Issued: 10/08/1991
• Est. Priority Date: 01/16/1990
• Status: Expired due to Term

• Current Assignee: The Whitaker Corporation (Meggitt PLC)
• Original Assignee: Carroll Touch Incorporated
• Inventors: Bartlett, Alan L.
• Primary Examiner(s): Weldon, Ulysses
• Application Number:
  US07/609,128
• Time in Patent Office: 341 Days
• Field of Search: 250/206, 340/530, 340/712, 340/762, 340/782, 340/802, 340/710, 340/718, 341/5, 341/26, 341/31, 315/164, 315/170, 315/173, 363/60, 368/83, 368/241, 368/67, 178/18
• US Class Current: 341/31
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen

Abstract

A touch input device, suitable for use in detecting the presence of an opaque element within a display area bounded by light emitting elements and light detecting elements includes light emitter activating circuitry in which the light emitting elements are individually selectable. Each light emitting element is contained within a matrix and source drivers and sink drivers are effective to select a specific row and column address for each individual light emitter. Current for the light emitters is provided by a voltage source which is chosen for compatibility with the logic used in the touch input system. A charge pump operating sequentially with the selection light emitting elements is used to establish a voltage greater than the normal supply voltage to overcome the voltage drops of the source and sink driver and the activated light emitter to insure light emission greater than a minimum threshold.

Claims

1. A touch input device for detecting the presence of an opaque element within an irradiated display area, comprising:

a plurality of light emitting elements individually aligned with a plurality of light detecting elements located on an opposite side of the display area so that a beam of light emitted by a respective one of said light emitting elements is detected by a respective one of said light detecting elements aligned therewith unless an opaque element is positioned between said light emitting element and said light detecting element aligned therewith thereby interrupting said emitted light beam;

means for processing the detection of light or absence of light by said light detecting elements to determine and indicate the absence of or at least the presence and location of a said opaque element, respectively;

a common voltage source generating a supply voltage;

means for sequentially activating individual ones of said light emitting elements to generate light beams traversing said display area and incident upon respective aligned ones of said light detecting elements; and

a common voltage enhancement means between said voltage source and said sequential activation means, said voltage source upon activation of a respective one of said light emitting elements being electrically connected in series with the negative side of a capacitor of said voltage enhancement means, and the positive side of said capacitor being connected in series with a respective one of said light emitting elements, upon said activation power thereby being transmitted to said one of said light emitting elements from both said voltage source and said voltage enhancement means simultaneously,

said voltage enhancement means establishing a voltage at the positive side of said capacitor during a time interval between activation of sequentially activated ones of said light emitting elements and establishing the supply voltage as a series additive pedestal voltage at the negative side of said capacitor upon activation of each said light emitting element so that the voltage on the positive side of said capacitor is greater than the supply voltage of said voltage source during activation of each said light emitting element, thereby being synchronous with said sequential activation,

whereby the common voltage enhancement means and common voltage source insure that the light emitted by each said light emitting element exceeds a minimum threshold, while synchronous operation of the voltage enhancement means results in generating minimal electrical noise and thereby maintaining the integrity of the functioning of the touch input device.

2. The touch input device of claim 1 wherein said light emitting elements are located on two sides of the display area and said light detecting elements are located opposite said two sides.

3. The touch input device of claim 1 wherein said sequential activation means comprises source driver means and sink driver means, said light emitting elements being electrically connected therebetween.

4. The touch input device of claim 3 wherein said light emitting elements are connected to said source driver means and said sink driver means in a matrix so that each said light emitting element is individually addressable.

5. The touch input device of claim 1 wherein each said light emitting element comprises a light emitting diode.

6. The touch input device of claim 1 wherein said voltage enhancement means comprises charge pump means including switch means connected between said voltage source, said light emitting elements and a negative side of said capacitor, said switch means being switchable between a first state and a second state, said switch means being in said first state during the interval between activation of respective ones of said sequentially activated light emitting elements and said switch means being then electrically connected between said voltage source and said capacitor for charging said capacitor, and said switch means being in said second state during activation of each said light emitting element and being then electrically in series between said light emitting element and both said voltage source and said capacitor, said capacitor being partially discharged by said switch means in said second state.

7. The touch input device of claim 6 wherein said switch means comprises a first transistor and a second transistor.

8. The touch input device of claim 1 wherein said voltage enhancement means comprises said capacitor, a first transistor and a second transistor, and a diode, said second transistor being connected between said voltage source and said negative side of said capacitor, said first transistor being connected between ground and said negative side of said capacitor, and said diode being connected between said voltage source and said positive side of said capacitor.

9. The touch input device of claim 8 wherein said first transistor is close circuited during the interval between activation of said sequentially activated light emitting elements to establish a first voltage at the positive side of said capacitor.

10. The touch input device of claim 9 wherein said first transistor is open circuited and said second transistor is close circuited when each said light emitting element is activated to establish a pedestal voltage on the negative side of said capacitor.

11. Apparatus for detecting the presence of an opaque object, comprising:

sequentially activatable light emitting means generating light incident upon associated light detecting means;

means for activating said light emitting means including;

a common voltage source generating a supply voltage; and

a common voltage enhancement means between said voltage source and said light emitting means, said voltage source upon activation of a respective one of said light emitting means being electrically connected in series with the negative side of a capacitor of said voltage enhancement means, and the positive side of said capacitor being connected in series with a respective one of said light emitting means, upon said activation power thereby being transmitted to said respective one of said light emitting means from both said voltage source and said voltage enhancement means simultaneously,

said voltage enhancement means establishing a voltage on the positive side of said capacitor when said light emitting means are off and establishing the supply voltage as a series additive pedestal voltage at the negative side of said capacitor upon activation of each said light emitting means so that a voltage greater than said supply voltage is available for activating said light emitting means, thereby being synchronous with sequential activation of said light emitting means,

whereby the common voltage enhancement means and common voltage source insure that the light emitted by each said light emitting means exceeds a minimum threshold, while synchronous operation of the voltage enhancement means results in generating minimal electrical noise and thereby maintaining the integrity of the functioning of the apparatus.

12. The apparatus of claim 11 wherein said means for activating said light emitting means for activating said light emitting means is adapted to sequentially activate said light emitting means.

13. The apparatus of claim 12 wherein said means for sequentially activating said light emitting means includes logic means responsive to said supply voltage.

14. The apparatus of claim 13 wherein said means for sequentially activating said light emitting means comprises a source driver and a sink driver controlled by said logic means.

15. The apparatus of claim 14 wherein said logic means further comprises a microprocessor supplying activating signals to said light emitting means and to said voltage enhancement means.

16. The apparatus of claim 11 wherein said supply voltage is five volts and the voltage provided to a said light emitting element from said voltage source and said voltage enhancement means in series therewith during activation thereof is greater than five volts.

17. The apparatus of claim 11 wherein said light emitting means comprises a plurality of light emitting elements and said light detecting means comprises a plurality of individual light detecting elements.

18. The apparatus of claim 17 wherein said light emitting elements are configured in an individually addressable matrix, each said light emitting element being addressable by source driver means and sink driver means.

19. The apparatus of claim 18 wherein said light emitting elements comprise light emitting diodes.

20. The apparatus of claim 11 wherein said voltage enhancement means comprises said capacitor, a first transistor and a second transistor, and a diode, said second transistor being connected between said voltage source and said negative side of said capacitor, said first transistor being connected between ground and said negative side of said capacitor, and said diode being connected between said voltage source and said positive side of said capacitor.

21. A touch input device for detecting the presence of an opaque element, comprising:

a plurality of sequentially activatable light emitting elements individually aligned with a plurality of light detecting elements, light from each one of said light emitting elements being incident upon an associated one of said light detecting elements unless interrupted by the presence of an opaque object;

means for activating said light emitting elements including;

a common voltage source generating a supply voltage;

a common charge pump means switchable between a charge mode and an activating mode, said charge pump means being electrically connected in series with said voltage source to a respective one of said light emitting elements upon activation thereof by said activation means to transmit power to said one of said light emitting elements from both said voltage source and said charge pump means simultaneously, said charge pump means adapted to store a voltage of up to an amount approximately equal to said supply voltage during said charge mode, and during said activating mode to supply power to a said respective one of said light emitting elements at a voltage greater than said supply voltage; and

control means for generating a first signal and a second signal, said fist signal selecting an individual one of said light emitting elements, each said individual one of said selected light emitting elements being activated by changes in said second signal and said charge pump means being switched from the charge mode to the activating mode by changes in said second signal and thereby being synchronous therewith,

whereby the common charge pump means and common voltage source insure that the light emitted by each said light emitting element exceeds a minimum threshold, while synchronous operation of said charge pump means results in generating minimal electrical noise and thereby maintaining the integrity of the functioning of the touch input device.

22. The touch input device of claim 21 further including driver means responsive to said first signal from said control means, for selecting an individual one of said light emitting elements.

23. The touch input device of claim 22 wherein said driver means comprises source driver means and sink driver means.

24. The touch input device of claim 23 wherein said source driver means is selectively connected to said light emitting elements in a plurality of rows and said sink driver means is selectively connected to light emitting elements in a plurality of columns, said rows and columns forming a matrix in which each said light emitting means is individually selectively addressable.

25. The touch input device of claim 24 wherein said control means is responsive to said supply voltage.

26. The touch input device of claim 21 wherein said charge pump means is adapted to store a voltage by including a capacitor and a switch means connected between said voltage source, said light emitting elements and a negative side of said capacitor, said switch means being switchable between a first state and a second state, said switch means being in said first state during the interval between activation of respective ones of said sequentially activated light emitting elements and said switch means being then electrically connected between said voltage source and said capacitor for charging said capacitor, and said switch means being in said second state during activation of each said light emitting element and being then electrically in series between said light emitting element and both said voltage source and said capacitor, said capacitor being partially discharged by said switch means in said second state.