JPH0351857Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a capacitive keyboard using capacitive switches that detect key operations by changes in capacitance.

[Technical background of the invention and its problems]

Conventionally, for example, many keys were arranged in a flat manner,
A so-called keyboard is known in which predetermined characters such as alpha alphabets, numbers, symbols, codes, etc. are assigned to these keys, and coded signals corresponding to the preset characters are sent out in response to the operation of these keys. It is being The structure of such a keyboard generally uses mechanical contacts. By the way, recently, capacitive switches that have good durability and excellent key touch are also being used. This capacitive switch uses a sense amplifier to amplify changes in capacitance between electrodes caused by key operations to obtain on/off signals for the key. Conventionally, when the matrix signal line is long, such as in a capacitive keyboard using such a capacitive switch, the impedance is high and in a system that handles minute signals, static electricity noise generated by the operator is a problem. , noise from the power line,
There was a possibility that malfunctions would occur due to noise caused by external electric and magnetic fields. Therefore, in order to prevent malfunctions due to such noise, it is important to perform impedance matching of the signal lines.

Therefore, when terminating (grounding) a switch far from the drive of a capacitive keyboard with a resistor, two
terminating resistors are required, which means that twice as many terminating resistors as the matrix are required. However, mounting such a resistor is not possible due to the mounting cost or it is impossible to provide a resistor between the switches. As described above, there are manufacturing problems, and in reality, no countermeasures against noise have been taken at present.

[Purpose of invention]

This idea was made in view of the above circumstances,
The purpose is to easily add a matching resistor to a capacitive switch, to achieve impedance matching of the signal line, and to prevent malfunctions even when static electricity or other noise occurs. It is an object of the present invention to provide a capacitive keyboard which can be made resistant to noise and which can save space because a resistor is provided on the side surface of the through hole of the board.

[Summary of the idea]

This idea consists of a key matrix in which capacitive switches with counter electrodes are provided at the intersections of a matrix composed of a plurality of rows and columns on one side of the substrate, and a grounding member for grounding provided on the other side of the substrate. The counter electrode of the capacitive switch provided on one surface of the substrate and the grounding member provided on the other surface of the substrate are electrically connected by a resistor provided on the side surface of the through hole of the substrate. It was designed to connect to.

[Example of idea]

An embodiment of this invention will be described below with reference to the drawings.

In FIG. 1, 1 is a key matrix,
Capacitive keys (capacitive switches) _C11 , _{C12 ,} . Note that the number of keys may be appropriately provided depending on the rows and columns, and there may be blank spaces.

Drive signals are sequentially and selectively applied to each row by a line drive circuit 2.

The line drive circuit 2 outputs first and second drive signals for one row in synchronization with the first and second sampling pulses output from the microprocessor 5. Further, the signals from each column are sequentially and selectively outputted to a sense amplifier 4 by a multiplexer 3. The line drive circuit 2 and multiplexer 3 are each driven by an address signal from a microprocessor (MPU) 5.
Each key C ₁₁ . . . is designated one by one. In this case, while a drive signal is being applied to a particular row by the line drive circuit 2, the multiplexer 3 selects every column once, and each time the row to which the drive signal is applied is updated. It's becoming repetitive. The sense amplifier 4 amplifies the minute signal supplied from the multiplexer 3 to the voltage level of the logic circuit and converts it into a logic signal. The minute signal generated by the above key C ₁₁ ... depends on the key press state.
In other words, the hysteresis changes depending on the capacity. As a result, for example, when a key is pressed completely, the sense amplifier 4 outputs a signal for several microseconds, and when the key is pressed shallowly, a signal of several microseconds or less is output depending on the position of the key. ing.

The sense amplifier 4 outputs a logic signal in response to the first drive signal, and outputs a logic signal in response to the second drive signal. The output of the sense amplifier 4 is supplied to one input terminal of NAND circuits 6 and 7. The other input terminals of the NAND circuits 6 and 7 are supplied with a first sampling pulse and a second sampling pulse output from the microprocessor 5, respectively. The above NAND circuit 6,
The output terminals of 7 are connected in common, and are connected to a power supply +V (not shown) via a resistor 8, as well as to an interrupt signal input terminal (INT) of the microprocessor 5.

Further, when the microprocessor 5 outputs an address for a predetermined key, if an interrupt signal is supplied to the input terminal INT by outputting the first sampling pulse, it then outputs a second sampling pulse, and then outputs the second sampling pulse. When an interrupt signal is supplied to the input terminal INT by the output, it is determined that the key at that address has been pressed, and the result of this determination is output to the data bus 9. At this time, if no interrupt signal is supplied to the input terminal INT for the output of the first sampling pulse or the second sampling pulse,
It does not determine that a key has been inserted, and moves on to processing for the next address.

Next, using Figures 2 to 4, press key C ₁₁ ...
The configuration will be explained in detail. That is, it has a pair of fixed electrodes 12 and 13 fixed to the upper surface of the printed circuit board 11 so as to face each other and to be spaced apart from each other by a predetermined distance. Each of the fixed electrodes 12 and 13 is formed from a substantially semicircular copper pattern, with each chord facing each other. A dielectric material 14 as an insulator is attached to the upper surfaces of both fixed electrodes 12 and 13. Furthermore, an auxiliary electrode 15 is placed on the dielectric 14 in the area defined by both the fixed electrodes 12 and 13. The auxiliary electrode 15 is composed of a conical coil spring whose strands have a circular cross-section, and as the button 20 is pressed, the dielectric 1
It is designed to come into contact with both fixed electrodes 12 and 13 via 4. Further, a ground 16 serving as a grounding member is fixed to the lower surface of the printed circuit board 11. This earth 16 and the fixed electrodes 12, 13
The terminals 17 ₁ and 17 ₂ are through holes 19 respectively.
It is electrically connected via a conductive paste 18 such as silver paste, copper paste, carbon paste, etc. as a resistor coated on the inner wall surface. This resistor 18 is used as a terminating resistor, and its resistance value is, for example, 5 kΩ to 10 kΩ. As a result, the equivalent circuit for each row of the key matrix is as shown in FIG. 5, in which a terminating resistor R _S is connected to both ends of the key. Therefore, impedance matching of the signal lines can be achieved, and malfunctions can be prevented even if noise such as static electricity occurs.

In such a configuration, at the position shown in FIG. 2, the opposing areas of both fixed electrodes 12 and 13 facing each other with the dielectric 14 in between are small. Therefore,
The capacitance defined between these electrodes 12 and 13 is small. By pushing the button 20 from this position with your finger, the auxiliary electrode 15 comes into contact with both fixed electrodes 12 and 13 via the dielectric 14, starting from the lowest part and in accordance with the amount of push and movement of the button 20. To go. As a result, the above-mentioned opposing area changes approximately in proportion to the amount of push-in movement of the button 20. That is, the capacitance defined between both electrodes 12 and 13 changes similarly. The maximum capacitance can be obtained at the position where the button 20 is pushed in the most.

Next, the operation in such a configuration will be explained. For example, assume that key C ₁₁ is now inserted. Then, in response to an address signal from the microprocessor 5, a first drive signal is applied from the line drive circuit 2 to the first column of the matrix.
This causes multiplexer 3 to
When the row is selected, the sense amplifier 4 outputs a logic signal according to the signal generated by the key _C11 . After a predetermined period of time has elapsed since the first drive signal was output, the microprocessor 5 outputs the first sampling pulse. As a result, a NAND circuit 6 is established, and an interrupt signal is supplied to the input terminal INT of the microprocessor 5. This interrupt signal causes the line drive circuit 2 to apply a second drive signal to the first column of the matrix. As a result, when the multiplexer 3 selects the first row of the matrix, the sense amplifier 4 outputs a logic signal in response to the signal generated by the key _C11 . Then, after a predetermined period of time has elapsed since the second drive signal was output, the second sampling pulse is output from the microprocessor 5. As a result, a NAND circuit 7 is established, and the input terminal of the microprocessor 5
The interrupt signal is supplied to INT again. In response to this interrupt signal, the microprocessor 5 determines that the key C ₁₁ corresponding to the address has been pressed, and outputs the result of this determination to the data bus 9.

Next, the microprocessor 5 determines that the key _C11 has been released, and then determines the next input key.

Also, if another key C ₁₂ ... is inserted,
Similarly, it is designed to be judged based on its operation.

[Effect of idea]

As detailed above, according to this invention, it is possible to easily add a matching resistor to a capacitive switch, and it is possible to perform impedance matching of the signal line, thereby preventing malfunctions even if noise such as static electricity occurs. It is possible to provide a capacitive keyboard that can prevent noise from occurring, is resistant to noise, and can save space because the resistor is provided on the side surface of the through hole of the board.

[Brief explanation of drawings]

The drawing shows one embodiment of this invention.
The figure is a block diagram schematically showing the overall configuration.
Figures 4 to 4 are diagrams for explaining the configuration of the keys,
FIG. 5 is a diagram showing an equivalent circuit for each row of the key matrix. 1... Key matrix, C ₁₁ ~... Key (capacitive switch), 11... Printed circuit board (substrate), 12, 13... Electrode, 14... Dielectric,
15... Auxiliary electrode, 16... Earth (grounding member),
17 ₁ , 17 ₂ ... terminal, 18 ... conductive paste (resistor), 19 ... through hole.

Claims (1)

[Claims for Utility Model Registration] (1) A key matrix in which capacitive switches each having a counter electrode at the intersection of a plurality of rows and columns are provided on one surface of the substrate, and a key matrix on the other surface of the substrate. In a capacitive keyboard having a grounding member for grounding, the counter electrode of the capacitive switch provided on one surface of the substrate is electrically connected to the grounding member provided on the other surface of the substrate. A capacitive keyboard characterized in that a resistor is provided on a side surface of the through hole of the substrate. (2) The capacitive keyboard according to claim 1, wherein the resistor is made of a conductive paste such as copper paste, silver paste, or carbon paste.