JPS6371715A - Instrument for measuring contact resistance value of keyboard contact - Google Patents

Abstract

PURPOSE:To surely operate a measuring instrument with a simple constitution to measure the contact resistance value of a keyboard contact by flowing a constant current from one side of a terminal train to measure voltages in both ends of the contact and detecting the contact resistance of the contact. CONSTITUTION:All contacts of a keyboard contact group 1 are turned on by a prescribed method like pressing to a plane plate. Connections of switches 8 to a transverse terminal row are fixed and those to a longitudinal terminal row are successively switched. They are switched in the order preliminarily reported to a microprocessor or by switching relays or the like by the control of the microprocessor. Since a constant current flows from a constant current source circuit 6 through the contact resistance of the contact which is changed in the transverse direction at each time of switching, voltage drop is detected. The voltage drop value is amplified by an amplifier 7 to facilitate performing the following processing and is measured by a microprocessor 2 or the like. The contact has a large contact resistance value and is judged too be defective if the voltage drop value larger than a prescribed value is generated for this contact.

Description

[Detailed description of the invention] [+Already required] When a membrane sheet is used when the keyboard contacts are turned on, a constant current is applied from one side of the terminal row, the voltage across the contacts is measured, and the contact resistance of the contacts is calculated. Knowing this will ensure keyhole inspection.

[Industrial Field of Application] The present invention relates to a device for measuring contact resistance when the contacts are turned on in a keyboard using a membrane sheet.

In conventional keyboards using membrane sheets, even when the contacts are turned on, the contact resistance value is quite large, which can lead to erroneous key operations, and it has been desired to determine accurate contact resistance values in the inspection process.

[Prior Art] Membrane sheets have come to be used as contacts provided on keyboards in order to reduce costs, instead of using mechanical contacts. When using a membrane sheet, a large number of contacts can be easily constructed by overlapping sheets on which conductors are printed so that the conductors are perpendicular to each other. However, when the contact is turned on, the contact resistance between the conductors becomes extremely large, reaching several thousand times that of a mechanical contact. In that case, a keyboard test circuit having the configuration shown in FIG. 3 was used to determine whether it was practical or not. This is because when using a membrane sheet, a part of the inspection process can be omitted by testing the membrane sheet when it is incorporated into the keyboard instead of inspecting it in a combined state. In FIG. 3, 1 is a keyboard contact group, Xi, X2...Xn are horizontal terminal rows, Yl, Y2...Yn are vertical terminal rows,
2 is a microprocessor, 21 is its IO board, 3 is a decoder, 4 is an encoder, 5 is a pull-up resistor (approximately 10Ω) connected to the horizontal terminal row, and the keyboard contact group is a contact at the intersection of the matrix. When the contact is turned on, the microprocessor 2 sends a signal (scan signal) to scan the terminal array from its 10 ports 21. First, in the decoder 3, for example, 10
When 10 is input, it is decoded and the "5" terminal is set to 1L.
Set it to 3. The other terminals remain high. Therefore, Yl
The zero-order encoder 4, where the potential of the terminal row becomes ``L''
The potential on the contact side corresponding to the scanning signal input to is “L”
The resulting value is displayed on the output terminal 0υT of the encoder 4 and notified to the microprocessor 2.

Therefore, the encoder 4 operates like a so-called selector. The contact side of the encoder 4 is always held at "H" by a pull-up resistor 5. Therefore, if a bit string from 000 to 101 is input to the encoder 4 from the microprocessor 2, the X terminal of the terminal string of Yl is turned on, so its potential "L" is detected, and the encoder inputs it. The contact operating position can be determined from the bit string.

[Problems to be Solved by the Invention] In the circuit shown in FIG. 3, the contact side terminals of the encoder 4 detect that the potential of the contact terminal row changes from "H" to "L", and It is necessary to display it on the output terminal OUT. At this time, a TTL circuit using a semiconductor element is often used as the encoder 4. Therefore, the potential “H”
If the change from "" to "L" was not large enough, an incorrect judgment could be made.The change in potential is related to the voltage of the power supply used, the connection resistance value, and the circuit configuration, so it is important to ensure that the circuit operates correctly. The design was difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus which improves the above-mentioned drawbacks, operates reliably with a simple configuration, and is capable of measuring the contact resistance value of keyboard contacts.

Means for Solving Problem E] FIG. 1 is a diagram showing the principle configuration of the present invention. In Fig. 1, the number is a matrix of keyboard contacts,
, X 2 -X n is a horizontal terminal row, yi.

Y2...Yn is a vertical terminal array, 2 is a microprocessor that can record measurement results, 6 is a constant current source circuit, 7
8 is an amplifier, and 8 is a switching switch that selectively opens and closes the horizontal terminal row and the vertical terminal row.

The configuration of the present invention is as follows: vertical terminal row Y1. Y2...- or horizontal terminal rows X1, X2-...
- a constant current source circuit 6 connected to one of the terminals, an amplifier 7 connected to both of the terminal rows, and a switching switch 8 for each terminal.
The output of the amplifier 7 is sent to the microprocessor 2.
, and measure the contact resistance value of the keyboard contacts.

[Operation] In FIG. 1, all of the keyboard contacts are turned on in a predetermined manner, such as by pressing a flat plate. Next, fix the connection with the horizontal terminal row for the switching switch 8,
Switch the vertical terminal rows sequentially. The switching order is carried out as notified to the microprocessor in advance, or relays etc. are switched under the control of the microprocessor. Since a constant current flows from the constant current source circuit 6 through the contact resistances of different contacts in the lateral direction each time the switch is switched, a voltage drop can be detected.

Therefore, the voltage drop value is amplified by the amplifier 7 and measured by the microprocessor 2 to facilitate the next processing. A contact that causes a voltage drop larger than a predetermined value has a large contact resistance value and is determined to be defective.

[Embodiment] FIG. 2 shows an embodiment of the present invention. The same reference numerals as in FIG. 1 indicate the same elements. A switching circuit using a mechanical relay is used as the switching switch 8, and a differential amplifier is used as the amplifier 7. An analog/digital converter is connected to the output of the differential amplifier 7. The switching switch 8 is provided with two circuits of relay contacts in parallel, a constant current is passed through one circuit, and a voltage drop is extracted from the other circuit. The voltage drop extraction terminal side is connected to the differential amplifier 7. A scan number is applied from the microprocessor 2 to the relay drive circuit, the drive circuit includes a decoder circuit, and predetermined relays are driven in the same manner as in the case of FIG. As mentioned above, the relay drive circuit fixes one of the X-direction terminal rows and Y-direction terminal rows, scans the other, and repeats one scan and then moves the fixed side one place to continue scanning. It is preferable that the constant current source circuit 6 be capable of setting a constant current from the microprocessor 2. This is because when the keyboard is in very good condition, the settings are changed to ensure that a larger current is required to check.

[Effects of the Invention] Thus, according to the present invention, a constant current is passed through a contact that is turned on, and a contact that causes a voltage drop of less than a predetermined value is considered to be good, and a contact that causes a voltage drop of less than a predetermined value is considered to be defective. It can definitely be processed. In addition, in the case of contacts that use membrane sheets, it is sufficient to test them after incorporating them into the keyboard, which has the effect of partially omitting the inspection process.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 3 is a diagram showing the configuration of a conventional device. 1.-Keyboard contact group Xl, X2..-Xn.--Horizontal terminal row Y1,
Y 2-=Y n -Vertical terminal row 2...Microprocessor 3...Decoder 4...Encoder 6 Constant current source circuit 7...Amplifier 8-Switch switch

Claims (1)

[Claims] Vertical terminal row (Y1) for keyboard contact group (1)
(Y2)...(Yn) or horizontal terminal row (X1
) (X2)... (Xn), a constant current source circuit (6) connected to one side, an amplifier (7) connected to both, and a switching switch that can be turned on and off for each terminal row. 1. A contact resistance value measuring device for keyboard contacts, comprising: an amplifier (8), and measures a contact resistance value of the contacts of the keyboard using the output of the amplifier (7).