JP2007207531A - Capacitance type touch switch device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitance type touch switch device of low power consumption type which can be driven by a battery, free from erroneous operation even if water is splashed on a panel. <P>SOLUTION: On a panel part made of an acrylic plate (polycarbonate or glass is also acceptable), a piezo-electrode having piezoelectric effect is mounted on a sheet formed by printing a switch electrode on a PET film. A control part is constituted of a piezo-electrode driving circuit capable of discriminating pressed state of the panel switch from non-pressed state thereof, a calculation circuit measuring changing amount of capacitance at contact state and non-contact state, and a CPU in which a nonvolatile memory storing the changing amount is built in. The capacitance type touch switch device of low power consumption, free from erroneous operation even if water is splashed on the panel, capable of bringing the calculation circuit and the CPU measuring the changing amount of capacitance into non-operational state until it becomes non-operation state by the result of calculation and pressing state, is provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a capacitive touch switch that employs a capacitive method as an input method.

The conventional capacitive touch switch shown in FIG. 1 includes a panel switch and a control board. The panel switch is configured by attaching an electrode sheet obtained by printing a silver paste on the PET film shown in FIG. 2-1 to a dielectric made of acrylic or glass with an adhesive (double-sided tape or the like). (Figure 2-2)
When a finger (conducting member) approaches the panel switch shown in FIG. 3A, a parallel plate capacitor in which a dielectric is sandwiched between the electrode and the finger is formed, and the capacitance increases. On the contrary, when the finger is removed from the panel, the capacitance decreases in contrast to this principle. The control board converts this change in capacitance into a voltage with a C / V (capacitance voltage) conversion circuit and replaces it with digital data with a CPU ADC (A / D converter). The general operating principle of the capacitive touch switch determines the state.
However, as shown in FIG. 3-2, when the surface of the panel switch is splashed with water and water droplets are formed, the water is also conductive, and as in the state where the finger is approached, the capacitance increases and causes malfunction. .

Patent registration No. 2887336.

Therefore, in the conventional method, when water droplets are applied to the surface of the panel switch, a change in capacity occurs, and a malfunction occurs when the change is similar to the state touched by a finger.
Therefore, as a measure to prevent water from splashing on the panel switch, the surface of the panel switch is inclined so that water droplets can flow quickly, and a convex surface is provided only on the panel surface switch to provide water repellent treatment. Is the current situation. However, when the surface of the panel switch is inclined, in places where water is continuously splashed, such as a shower, water cannot be burned and capacity changes occur, preventing malfunction. In addition, even if a projection is partially provided on the surface of the panel switch, it is effective for a small switch, but if a large switch is used, water splashes and water droplets are produced, resulting in a change in capacitance, which cannot prevent malfunction. . For this reason, the surface shape is limited and the panel switch is poor in versatility and difficult to use, and the problem cannot be solved sufficiently.
The operation of the conventional capacitive touch switch shown in FIG. 1 operates a C / V conversion circuit to measure a change in capacitance, converts the value into digital data by a CPU ADC, On / Off of the switch is determined from the result of the calculation. For this reason, even when the switch is not pressed, it is difficult to reduce power consumption when the control board is always in an operating state, and it is difficult to commercialize a battery-driven capacitive touch switch.
Therefore, the present invention aims to solve the above-mentioned problems, and when used outdoors or around water, it does not malfunction even if water drops and water drops are formed, and the capacitance type that does not limit the size and shape of the switch It is intended to provide a low power consumption type capacitive touch switch that can be driven by a battery even if it is mounted on a switch unit such as a remote control or a gas range where it is difficult to take an AC power supply.

  In order to achieve the above object, in the present invention, in a capacitive touch switch, a switch electrode is printed with a silver paste on a PET film, and an electrode sheet on which a piezoelectric electrode is generated that generates a voltage due to the piezoelectric effect when further curved is created. The panel switch is bonded to an acrylic plate or glass plate (dielectric) with an adhesive, and the panel switch is set to a threshold value of the voltage value of the piezo electrode in a pressed state and a non-pressed state by a finger (conducting member). From a control board equipped with a non-volatile memory that stores the amount of change in both the voltage value and the capacitance. An electrostatic capacitance type touch switch device is proposed.

According to the present invention, in order to prevent malfunction due to water droplets of a capacitive touch switch, the panel switch has a simple panel structure without being inclined or having a convex curved surface on the surface of the switch for water repellent treatment. In addition, it is possible to provide a capacitive touch switch that does not malfunction even when water is applied to the panel switch.
In terms of power consumption, only the piezoelectric element drive circuit operates while waiting for input until the panel switch is pushed by the finger and bends, and the CPU and the capacitance change circuit do not need to operate. A drivable capacitive touch switch can be provided.

The present invention comprises a panel switch and a control board as shown in FIG.
A panel switch is an electrode sheet in which a switch element and a GND electrode are printed on a PET film, and a piezoelectric element is attached to the film with a double-sided tape or the like (FIG. 4-1). The electrode sheet is a glass plate or an acrylic plate (dielectric). Moreover, it becomes a pasting structure with an adhesive.
As the adhesive employed in the present invention, any adhesive having a bonding effect such as a double-sided tape, glue, or bond may be used.
The switch electrode is printed with a silver paste on a PET film so as to hide a human finger, and a capacitance change occurs between the finger (conducting member) and the electrode.
The purpose of the GND electrode is to reduce the noise and stabilize the signal level by patterning a silver electrode around the panel.
For the piezoelectric element, a piezo film that is easily bent and attached is used. A piezo film has a property of generating a voltage due to a piezoelectric effect when it expands and contracts, and a rectangular piezo film is attached in parallel to the upper or lower portion of a switch electrode to form a piezo electrode. This electrode sheet with piezo electrodes is attached to the back of the panel switch with double-sided tape. Piezo electrodes are expanded and contracted by the pressure of pressing a panel switch with a finger, generating a voltage. Due to the nature of the piezoelectric effect, this piezo electrode generates a voltage that is directly proportional to the rate at which the panel switch bends. The control board is connected to the CPU when the voltage generated at the piezo electrode exceeds a preset threshold. Piezo drive circuit for generating an interrupt (INT) signal, switch electrode switching circuit for sequentially connecting switch electrodes to the oscillation circuit, C / F conversion circuit for converting capacitance change using the oscillation circuit to frequency change, CPU I / O control signal for selecting operation / non-operation of C / F conversion circuit, non-volatile memory for storing threshold data, and CPU with built-in input capture function capable of measuring waveform width .

Embodiments of the present invention will be described below with reference to the drawings. First, a method for determining the non-pressure state and the pressing state of the panel switch will be described with reference to FIG. One end of the piezo electrode is connected to GND, and the other end on the opposite side is connected to the + terminal of the C-MOS type OP amplifier. R1 is a resistance for generating a voltage of a piezoelectric electrode and requires a high resistance of 100 MΩ, and a low power consumption type C-MOS type OP amplifier is used as a non-inverting amplifier circuit in order to amplify the generated voltage. Since the amplification factor is a non-inverting amplifier circuit, it is (R3 / R2) +1 and becomes a threshold value for determining how much the panel switch is bent and how much the switch is pressed.
When the panel switch in FIG. 6A is in a non-pressure state, the output voltage of the piezo electrode is 0V, so the output of the OP amplifier is also 0V and becomes a low level signal. Notifies that the panel switch is in the no-pressure state and does not activate the CPU.
When the panel switch in FIG. 6B is in the pressed state, a voltage is generated from the piezo electrode and is amplified by (R3 / R2) +1 times by the amplifier circuit. When the panel switch is bent until a voltage exceeding a predetermined threshold is generated, the INT signal becomes low level from the 74HC14 inversion circuit to notify that the panel switch is in the pressing state and activate the CPU.

Next, a method of measuring the amount of change in the capacitance of the switch electrode when the finger is in contact with or not in contact with the panel switch will be described with reference to FIG.
In a non-contact state where the finger does not touch the panel switch, that is, in the switch OFF state, a control signal is output from the CPU I / O terminal 2 to the electrode switching circuit, and SW1 to SW6 are sequentially connected to the C / F conversion circuit. Then, the oscillation frequency at that time is measured, and the values of the transmission frequencies Toff-1 to Toff-6 in each switch OFF state are stored in a nonvolatile memory connected to the I / O terminal 1 of the CPU.
Next, in the contact state where the finger touches the panel switch, that is, the switch is ON, a control signal is output from the I / O terminal 2 of the CPU to the electrode switching circuit, and SW1 to SW6 are sequentially supplied to the C / F conversion circuit. The oscillation frequency at the time of connection is measured, and the transmission frequencies (FIG. 8) Ton-1 to Ton-6 in each switch ON state are stored in a non-volatile memory connected to the I / O terminal 1 of the CPU.

Individual initial data of the measured electrode panel is incorporated in the nonvolatile memory of the CPU and is as follows.
1) Oscillation frequency when switch is OFF (Figure 9-1)
・ Capacity C = C1
・ Resistance value R = R1
・ Frequency Toff-1, 2, 3, 4, 5, 6 = about 100kHz 2) Oscillation frequency when switch is on (Figure 9-2)
・ Capacity C = C1 + C2 (Capacity increase due to finger touch)
・ Resistance value R = R1
-Frequency Ton-1,2,3,4,5,6 = 99 kHz As an example, the determination method will be described using the specific circuit of FIG. 10 when SW2 is pressed.
When SW2 is pressed, the piezo electrode is bent, the output value of the OP amplifier exceeds the threshold value, and an INT signal is generated from the inverting circuit of 74HC14 to the CPU. When a low level signal is input to the INT terminal of the CPU, the CPU that has been stopped in the standby mode is activated, and the stop signal of the transmitting circuit is canceled at the I / O terminal 3 of the CPU according to the program built in advance. The TLC 555 includes a multivibrator circuit as an oscillation timer IC.
Next, a control signal is output from the I / O terminal 2 of the CPU to the electrode switching circuit, connected to the C / F conversion circuit in the order of SW1 to SW6, and the oscillation frequency at that time is measured. Since SW1 = SW3 = SW4 = SW5 = SW6 = 100 kHz and the same frequency as Toff, it can be determined that the switch is OFF. SW2 is the same as Ton at 99 kHz and can be determined to be a switch ON because of the frequency.

Due to this principle, even if water is applied to the panel switch and water droplets are formed, the panel does not bend, so no voltage is generated from the piezo electrode, and the capacitance conversion circuit (C / F conversion circuit) is inactive, so the capacitance The type touch switch can prevent malfunction.
Further, when the panel switch is in the non-pressure state, that is, the switch is in the input state, the CPU can be set in the standby mode and the transmission circuit can be stopped, so that the low power consumption mode can be realized and the battery can be driven.

FIG. 3 is a structural diagram of a capacitive touch switch. Panel structure diagram. Capacitance change mechanism. Panel switch with piezo electrode. The system block diagram of the electrostatic capacitance type touch switch with a piezo electrode. Piezo electrode drive circuit. Switch electrode capacitance variation measuring circuit configuration diagram. Capacitance change measurement circuit (C / F conversion circuit) with finger in contact. Change in oscillation frequency due to capacitance change. The block diagram of an electrostatic capacitance type touch switch.

Explanation of symbols

1 Transmission circuit
2 CPU
3 I / O terminal 4 Electrode switching circuit

Claims (2)

In capacitive touch switches, a switch electrode is printed with silver paste on a PET film, and an electrode sheet on which a piezoelectric electrode is generated that generates a voltage due to the piezoelectric effect when it is further curved, is an acrylic plate or glass plate (dielectric) A panel switch pasted with an adhesive to the panel switch, with a finger (conducting member) against which the voltage value of the piezo electrode is set as a threshold value in a pressed state and a non-pressed state, and a pressure state and no pressure Capacitive touch characterized by comprising a control board equipped with a non-volatile memory that stores the amount of change in both voltage value and capacitance in an arithmetic circuit that measures the amount of change in capacitance of the switch electrode in a state Switch device. The capacitive touch switch is a CPU that does not operate an arithmetic circuit that measures a change in capacitance while the panel switch is in a no pressure state waiting for a switch input, and in a state where the voltage value of the piezo electrode exceeds a threshold value in a pressed state. The capacitive touch switch device according to claim 1, wherein power consumption can be reduced.