JPS60243427A - Key input unit for high frequency heater - Google Patents

Abstract

PURPOSE:To lower the cross talk noise along with a reduction in the cost using carbon as material for a conductive pattern of a membrane switch while a conductive pattern of an earth potential is formed between conductive patterns of a signal line. CONSTITUTION:A facing plate 7 and a plate 8 composes a conductor and grounded at the earth potential to perform an electrostatic shield against external noises while an earth pattern line 13 grounded at the earth potential is provided between signal lines of a carbon pattern to eliminate cross talk noises between the signal lines. Then, the conductive patterns are covered entirely with a metal material from the top and bottom thereof to achieve an electric shield thereby removing not only internal noises but effect of external noises on the signal lines. A drastic cost reduction of a membrane keyboard is possible by using an inexpensive material such as carbon, a high resistance conductor, as conductive material for the conductive patterns in place of silver.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an improvement in the key power section of a high frequency heating cooker equipped with an electronic control unit including a microcomputer, and the invention relates to an inexpensive and highly reliable key power means configuration. This is related to.

Configuration of conventional example and its problems Figure 1 is an external view of the high-frequency heating device. On the control panel 1, there is a membrane switch 2, which is a sheet-like key switch for setting and inputting the cooking type and time, and a screen that displays the cooking time. A fluorescent display tube 3 is arranged. The structure of this menglen switch will be explained with reference to FIG. A substrate made of insulator V6 with holes corresponding to the contact areas is placed between 4°50 square conductive pattern sheets on which conductive patterns and contacts are formed by printing or other methods on the insulator/-. On the conductive pattern sheet 4, a decorative panel 7 is arranged with the types of key switches written on it, and on the other hand, a metal plate 8 is arranged as a base material for reinforcing these sorted items. It is. These sheets are each adhesively fixed with an adhesive. Now, when a person presses the °' High Power 2' key as shown in Figure 2, the pressing force at that time corresponds to the corresponding "High Power" switch on the upper and lower 4%E pattern sheets 4 and 5. The contact part comes into contact with the opening of Nubesa 6, and the "High H power" switch is turned on. In conventional membrane switches, a low-resistance conductor such as silver has been used as the material for the conductive butter, conductors, and contact portions. The purpose of this was to minimize the resistance of the contacts and conductor parts, but the material cost of silver, which is a precious metal, was extremely high, and the emergence of inexpensive contact and conductor materials to replace silver was eagerly awaited. .

Purpose of the Invention The purpose of the present invention is to significantly reduce costs by using a high-resistance material such as carbon as a contact point or conductor material in place of silver in a membrane switch.

Structure of the Invention In order to achieve the above object, the conductive pattern of the membrane switch of the present invention is made of carbon, the input impedance of the key input circuit is increased to 100Ω, and the signal source impedance is made of carbon. In order to cope with the decrease in noise resistance due to the increased size, the conductive pattern of the membrane switch has an electrostatic shield structure, and between the conductive patterns of the signal line,
A conductive pattern at ground potential is formed to reduce crosstalk noise between signal lines.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The basic structure of the membrane switch is the second conventional example.
It is the same as the figure, except that the contacts and conductors are replaced with carbon instead of silver.The only difference is that the shape of the contacts and the width of the conductor pattern are wider and larger in order to minimize the resistance value of the carbon contacts and conductors. There is. In this way, one contact of the membrane switch is formed/+,,! 7
Although the resistance value varies depending on the number of membrane switches and physical dimensions, the limit is to keep it on the order of about 10 ohms. Considering that conventional silver contacts have a resistance of 500Ω or less, this is a very large value. Therefore, the input impedance of the key input circuit of the present invention is set to 100 Ω corresponding to the resistance value of the carbon contact 10 Ω.

FIG. 3 shows the M configuration of the control circuit section according to an embodiment of the present invention. Membrane switch 2 is 3X3=
It has 9 contacts, and the output ports of the microcomputer 9 are 1-R, 1-R.
The key scan output from 2 and R5 completes the key scan, and the human power information is 1- to 1. K2.
Input to K4. The internal resistance of the board of the microcomputer 9 is set to infinity, and an input resistor 10, RIN, is inserted into each input board as an input impedance. Now, if we consider the value of the contact 80 equivalent resistance, RKzY, of membrane switch 2 to be 15Ω, the signal lightning FF appearing at the input port is - (10n V rz /
t ---y −,, ++ to X 9 v= 7,
It becomes 87. Generally, in the case of a 9V type microcomputer, the limit voltage value for determining an input signal as "H" level is Vss
-3.5v=5.5v, and the signal voltage of 8v is a sufficient value to determine the 11 HI+ level.

If the value of this input impedance RIN is increased too much, it will become extremely weak against the I sound.

FIG. 4 is a timing chart of the key scan signal and the input signal of the boat when the contact 8 is pressed. Information on the contact point 8 appears on the boat 1 at the scan timing of R5.

By the way, when using the 1-bon pattern, as mentioned above, the pattern width becomes larger and the spacing between the signal patterns becomes narrower, and the stray capacitance between the patterns becomes several hundred picoF. growing. Therefore, as shown in Fig. 6, the stray capacitance between adjacent patterns cannot be ignored, and the patterns are electrostatically coupled to each other via the stray capacitance c1°C2. Boat R's Suei
·of! When the scan signal rises, an upward pulse is generated at the port 2 via the stray capacitance C1, and conversely, when the scan signal falls, a downward pulse is generated. Similarly, a pulse is generated via the floating capacitance C2 between the boat R6 and the boat R6.

Such so-called crosstalk noise cannot be distinguished from the original signal. As a result, signals cannot be processed correctly, and the system itself does not operate or malfunctions. Therefore, in the Metsubrene switch of the present invention, in order to eliminate the above-mentioned disadvantages caused by the increase in stray capacitance due to the carbon pattern, the decorative board 7 and the plate 8 are made of conductors as shown in FIG. By grounding them to earth potential, electrostatic shielding against external noise is performed, and as shown in FIG. 8, by providing an earth pattern line 13 grounded to earth potential between the carbon pattern signal lines, This eliminates crosstalk noise between signal lines. As a result, the noise pulse of the boat Ki shown in FIG. 6 disappears, and the correct waveform as shown in FIG. 4 is obtained.

By the way, as shown in FIG. 7, the structure of the electrostatic shield of the conductor pattern is such that the lower surface of the decorative panel 7 is made of a conductor, which is grounded to the main body chassis with a lead wire, etc. In addition to the method of grounding to the chassis in the same way, as shown in Figure 9, conductive pattern sheets 4 and 6 can be grounded.
By printing a conductor on the entire back side of the signal pattern, the back side is used as a grounding surface, and like the signal pattern on the opposite side, it is grounded to the chassis ground with a connector connection, and the electrostatic sea/L/l- There are ways to do this. By using this method, there is no need to make the downward direction of the decorative panel 7 or the plate a conductor, and there is no need for a lead wire for grounding to the main body chassis, which further reduces costs. .

Effects of the Invention According to the present invention, the following effects can be obtained. First, by providing an earth pattern grounded to the earth potential between the conductor patterns, the electrostatic coupling between the conductor patterns, which are signal lines, is reduced, and system malfunctions due to crosstalk noise are reduced. Next, by covering the entire conductive pattern with a metal body from below and electrically shielding it, it is possible to eliminate the influence of external noise on the signal line using only internal noise. Finally, as the conductive phase t1 of the conductor pattern, an inexpensive old system such as carbon, which is a high resistance conductor, can be used instead of silver.
This will result in significant cost reductions.

[Brief explanation of drawings]

Fig. 1 is an external view of the high-frequency heating device, Fig. 2 is an explanatory diagram of the structure of a membrane switch, Fig. 3 is a control circuit diagram of the high-frequency heating device according to an embodiment of the present invention, and Fig. 4 is a key scan Timing chart between Shinshichi and the incoming horn signal, No. 5
The figure is an explanatory diagram of stray capacitance between conductor patterns, and Figure 6 is an explanatory diagram of the state in which Talostok noise is generated due to the stray capacitance.
Figure 7 is an explanatory diagram of the electrostatic shielding configuration of the entire conductor bag;
FIG. 8 is an explanatory diagram of the installation of a ground pattern for removing Talostalk noise between the 7# patterns, and FIG. 9 is a diagram showing the configuration of an electrostatic shield. 1... Control panel, 2... Membrane switch,
3... Display 'W, 4 + 5... Conductive Bakun sheet, 6... Insulating spacer, 7... (111
1', Hane TV, S plate, 9 Microcomputer, 10
・Input boat human power impedance, 11...Low pressure 1-Lance, 12...High frequency oscillation sound; Control relay, 13゛Earth pattern. Names of 1st + 1st person Patent attorney 1st person Nakao 1st person and 1 other person
Figure 4 Figure 5 Figure 6 Figure 7

Claims (3)

[Claims] (1) A sheet-like keyboard composed of a conductive pattern including contact portions formed in the form of a sheet surface, and an insulating sheet disposed between the conductive pattern sheets, and a key scan signal generation A high-frequency heating device comprising a key human power section, a control section such as a microcomputer that controls cooking based on the key human power, and the conductive pattern is made of a high-resistance conductor such as carbon. Key human powered equipment. (2) A key manual device for a high-frequency heating device according to claim 1, wherein a metal body is arranged to cover the conductive pattern sheet of the membrane switch, and the metal body is grounded to an earth potential. (3) In the conductive pattern of the membrane switch, at least the adjacent conductive pattern and the conductive pattern J- are provided with a conductive pattern. Key manual equipment for the high-frequency heating equipment described in item 1 and item 4.