1. Field of the Invention
The present invention relates to a touch panel in an information processing apparatus, and more specifically to a circuit configuration of a touch panel that detects the coordinates of a position pressed on a touch panel, and yet more specifically to an analog-type touch panel that uses a resistive film and a method of detecting the coordinates of a pressed position on the touch panel.
2. Description of Related Art
In the past, this type of touch panel circuit in a computer was used as a circuit to provide a simple input means which was fitted over the display apparatus. As one means of improving ease of operation and simplifying the apparatus, a touch panel having a larger surface area than the display region of the display apparatus was used, the part of the touch panel that fell outside of the display region being divided into a number of subregions, these subregions taking the place of keyboard keys or pushbutton switches, so that when pressed, a specific function was executed, as would be executed by pressing a function key.
Existing configurations of an analog-type of touch panel include those which use a resistive film and those which make use of electrostatic capacitance. With a touch panel that uses a resistive film, two uniform resistive film are separated by a spacing by means of a minute spacer, so that when the resistive film is pressed, the resistive films make contact, resulting in a voltage gradient that is applied to one of the resistive films being read as a voltage at the other resistive film.
FIG. 8 is a block diagram that shows an example of a touch panel circuit of the past.
The touch panel circuit 1 of FIG. 8 is made up of an A-D converter (ADC) 11 that has its reference input voltage terminal 11b connected to a power supply voltage (VCC), a switch (switching means) 41 that connects the input 11a of the ADC 11 to either an electrode 31 of a resistive film 30 or to an electrode 21 of a resistive film 20 of the touch panel, a switching means 43 which switches on and off the connection between VCC and the electrode 21 of the resistive film 20, a switching means 44 that switches on and off the connection between VCC and the electrode 31 of the resistive film 30, a switching means 45 that switches on and off the connection between the electrode 32 of the resistive film 30 and ground (GND), a switching means 46 that switching on and off the connection between the electrode 22 of the resistive film 20 and ground, a CPU 12 that controls all of the above-noted switching means and the ADC 11, and a memory 13 into which is stored the voltage values read from the ADC 11 and the coordinate values derived from those voltage values.
The touch panel 2 is constructed so that when two transparent and uniform resistive films 20 and 30, which are spaced apart from one another by a minute spacer, are pressed so as to make contact with each other, a voltage gradient that is applied to one of the resistive films is read as a voltage at the other resistive film.
On the reverse side of the display region of the touch panel 2 is disposed a display apparatus such as a liquid-crystal display. The subregions 51 of outside the display region each have assigned to them a function key.
The operation of the touch panel circuit of the past is described below.
FIG. 9 is a flowchart which shows an example of the operation of the touch panel circuit of the past which is shown in FIG. 8.
First, the switching means 43 and switching means 46 for the purpose of reading the horizontal (X) coordinate of the pressed position are set to on, switching means 41 is connected to the a side, and other switching means are set to off (step SD1).
The ADC 11 is instructed to start an A-D conversion (step SD2), and when the A-D conversion has been completed (step SD3), the voltage value is read (step SD4), the voltage value is converted to a coordinate value (step SD5), and this is stored into the memory 13 (step SD6).
Next, the switching means 44 and switching means 45 for the purpose of reading the vertical (Y) coordinate of the pressed position are set to on, switching means 41 is connected to the b side, and other switching means are set to off (step SD7).
The ADC is instructed to start an A-D conversion (step SD8), and when the A-D conversion has been completed (step SD9), the voltage value is read (step SD10), the voltage value is converted to a coordinate value (step SD11), and this is stored into the memory 13 (step SD12).
Since both the X and the Y coordinate values of the pressed position are obtained at this point, a judgment is made as to whether the pressed position is within the display region (step SD13). If it is outside the display region, a further judgment is made as to in which subregion 51 is it located (step SD14), and the processing of the function key corresponding to that subregion 51 is performed.
In this manner, because the processing for the judgment of the pressed position on a analog-type of touch panel which uses resistive films is more complex than a judgment of keyboard input which is input as a digital value or pushbutton switch input, judgment for touch panel function key input requires more time than the time required for keyboard or pushbutton input.
Additionally, because the entire touch panel makes a conversion to coordinate values with some given quantizing accuracy, the resolution per unit length usable for such function as recognition of handwritten characters is reduced by to the extent of the existence of the part of the panel lying outside the display area.
For example, in the Japanese Unexamined Patent Publication (KOKAI) No. 1-318110, there is language which describes technology for changing the resolution per unit length or the coordinate detection region by changing the value or polarity of a voltage that is applied the electrode of a resistive film.
In the Japanese Unexamined Patent Publication (KOKAI) No. 7-182108, there is indicated a method of measuring, in a touch panel made from two opposing electrode sheets, the voltage at a pressed position via a capacitance.
However, because the voltage is measured via a capacitance, there were also the problems of the equipment and circuit becoming complex, and of needing to establish the timing of the measurement, resulting in the measurement requiring time to perform.
In a touch panel circuit of the past as noted above, because the judgment as to whether or not a pressed position is within the display region is only possible after both the X and Y coordinate values have been established, even outside the display region, where it is sufficient to merely discriminate several subregion, it is necessary to perform processing with the same resolution that is used for such functions as recognition of handwritten characters, thereby causing an unavoidable decrease in detection speed.
Additionally, because conversion to coordinate values is performed with a given quantizing accuracy over the entire touch panel surface, the resolution per unit length within the display region that is used for such functions as recognition of handwritten characters is lowered to the extent of the existence of the area outside the display region.
In view of the above-described drawbacks in the prior art, therefore, an object of the present invention is to provide a touch panel circuit that overcomes the drawbacks in the prior art, by reducing the detection time for function keys outside of the display area.
Yet another object of the present invention is to prevent a decrease in the resolution per unit length within the display area by the provision of function keys outside the display area.