JPS61261922A - Electrostatic capacity type keyboard - Google Patents

Abstract

PURPOSE:To avoid a wrong detection of a depression of a key, caused by a noise, by outputting an output corresponding to a depression of a key, extending over a scanning period of plural times from an input voltage holding circuit. CONSTITUTION:When a scanning signal Vd is sent out again from a driver 4 to X0 of a line 1, if a C00 key is depressed continuously in advance, an input signal Vi is amplified by an amplifier circuit and inputted to an anode of a diode 11. In case when the input signal is larger than a forward voltage of the diode, the input signal passes through the diode 11 and a capacitor 14 is further charged. When the scanning signal Vd is sent out by a necessary continuous number of times, an output voltage V0 is obtained in an output of a voltage follower circuit 15, and it is a sufficient potential for detecting a depression of a key by a keyboard controlling circuit 17.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a capacitive keyboard with excellent noise resistance.

(Prior Art) In general, a capacitive keyboard has a drive circuit that arranges the required number of capacitive keys on a key matrix consisting of rows and columns, and scans the rows of the key matrix by sending a scanning signal. , a multiplexer, a comparator or current amplification circuit, etc. connected to the column, a detection circuit that detects a key press, and a scan tie for these drive circuits and detection circuits to detect when a key is pressed. It consists of a keyboard control circuit that recognizes the press of a key and sends a defined code etc. to an external device.

Compared to keyboards that use conventional mechanical contacts, capacitive keyboards have a simpler structure because the key contacts are capacitive, and there is no inevitable chattering in the mechanical contacts, and there is no wear and tear on the key contacts. High reliability of contacts.

(Problem to be solved by the invention) However, as a problem unique to capacitive keyboards, it is difficult to maintain a large difference in the capacitance of the keys when the key is pressed and when the key is not pressed, and the capacitance is also very small. The detection circuit may malfunction due to noise caused by the electronic circuit within the keyboard itself or external noise. For this reason, it is necessary to be careful when detecting key presses on capacitive keyboards.
Measures such as "reading twice" are used.

However, even if these means are used, a capacitive keyboard having the above-mentioned detection circuit may malfunction due to noise.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above drawbacks, prevent a capacitive keyboard from malfunctioning due to noise, and provide a highly reliable capacitive keyboard.

(Means for Solving the Problems) The features of the present invention for achieving the above object include a plurality of capacitive keys arranged at each grid point constituting a matrix, and scanning and selection of rows and columns. In a capacitive keyboard having a selection means for sequentially selecting keys by switching, and a detection circuit for detecting and outputting a press signal of the selected key, the detection circuit is connected to an output of the selection means. an amplifier circuit, an input voltage holding circuit, a superimposition circuit that superimposes the output of the input voltage holding circuit and the output of the amplifier circuit as an input to the input voltage holding circuit, and a clearing circuit that clears the input voltage holding circuit. and outputting an output corresponding to a key press from the input voltage holding circuit over a plurality of scanning cycles until the circuit is reset.

(Function) In the above configuration, key scanning is sufficiently faster than manual key pressing, so the output of the selection means (input of the detection circuit) corresponds to a single pressing of the key. As a result, a plurality of press signals are generated for each scanning period. The superimposition circuit and the input voltage holding circuit superimpose (add) the output of the input voltage holding circuit in the previous scanning period and the press signal in the current scanning period, and input the result to the input voltage holding circuit. Therefore, the output of the input voltage holding circuit is a signal that rises stepwise in each scanning period in response to the depression of a key, and a sufficiently high output potential is finally obtained. On the other hand, when the input voltage holding circuit generates an output due to noise, the duration of the noise is short, so the potential resulting from the superimposition is sufficiently lower than the potential caused by pressing the key. Therefore, the output caused by pressing a key can be distinguished from the output caused by noise.

(Embodiment) FIG. 1 is a circuit diagram of a capacitive keyboard according to the present invention.

The key matrix consists of row 1 from XO to Xm, column 2 from Yo to Yn, and coo at the intersection of row 1 and column 2.
, CFL to Cmn capacitive keys 6 are arranged. Row 1 is connected to driver 4 and column 2 is connected to multiplexer 5. The output of the multiplexer 5 is connected to a resistor 6 and a transistor 80, and a resistor 7 is connected to the collector of the transistor 8 to form an amplifier circuit. The collector of transistor 8 is connected to the cathode of diode 100, the anode of diode 11, and the cathode of diode 16 via capacitor 9.

From the cathode of the diode 11, the collector of the transistor 12, the resistor 13, the capacitor 14 and the voltage
Connected to the in-phase input terminal of the follower circuit 15. Furthermore, the output of the voltage follower circuit 15 is
to the anode and keyboard control circuit 17. The keyboard control circuit 17 sends a row scan signal 19 to the driver 4, a column selection signal 20 to the multiplexer 5, and a reset signal 18 to the base of the transistor 12, and a voltage follower circuit 15.
Read the output signal 21 of.

Next, the operation of the circuit shown in FIG. 1 will be explained with reference to FIG. 2. FIG. 2 is a time chart of the circuit shown in FIG. Keyboard control circuit 17 to multiplexer 5
A column selection signal 20 is sent from the keyboard control circuit 17 to keep Yo in column 2 conductive, and a reset signal 18 is sent from the keyboard control circuit 17 to the base of the transistor 12 to discharge the charging voltage vc of the capacitor 14 to Ov.

Next, when the scanning signal Vd shown in FIG.

If the key is pressed, the scanning signal Vd is input to the input of the amplifier circuit as the input signal Vi shown in FIG. 2(2) and amplified by the amplifier circuit. The amplified signal is input to the anode of the diode 11, and the anode voltage of the diode 11 when there is no input signal before this input signal is Ov.

If the input signal is larger than the forward voltage of the diode 11, the input signal passes through the diode 11 and charges the capacitor 14 to the charging potential VC, which is then connected to the voltage follower circuit 1.
5 passes through the diode 16 and appears at the anode of the diode 11 as the potential ■s shown in FIG. 2(4). Therefore, the anode potential and cathode potential of the diode 11 are the same potential, and the charging potential of the capacitor 14 is maintained at vc. Immediately after the above operation, the scanning signal V is sent from the driver 4.
d as X in row 1. When the COO key is pressed down again, the input signal Vi is amplified by the amplifier circuit and inputted to the anode of the diode 11, but the anode voltage s of the diode 11 and the charging voltage VC are
Since the follower circuit 15 holds the same potential, if the input signal is larger than the forward voltage of the diode 11, the input signal passes through the diode 11 and further charges the capacitor 14. If the scanning signal Vd is applied the necessary number of consecutive times, the output of the voltage follower circuit 15 will be as shown in Fig. 2 (5).
An output voltage ■o is obtained, which is a sufficient potential for the keyboard control circuit 17 to detect the depression of a key. If a noise larger than the forward voltage of the diode 11 is input to the anode of the diode 11 even though no key is pressed, an output voltage Vo shown by the dotted line in FIG. - The control circuit 17 does not reach the potential required to detect a key press. Further, when no key is pressed and no noise is generated, the output voltage vo is oV.

After the above operations, the keyboard control circuit 17 reads the output voltage ■o, detects the press of a key, and completes the press detection of the COO key of the capacitive key 6. Next, Co
Detection of presses of keys 1 to Cmn is performed sequentially using the method described above.

(Effects of the Invention) As explained in detail above, according to the present invention, the difference between the output voltage of the detection circuit when a key is pressed and the output voltage when the key is not pressed can be made large even if noise is mixed in. This makes it possible to avoid erroneous detection of key presses due to erroneous detection, and to provide a highly reliable capacitive keyboard.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a time chart showing the operation of the embodiment of FIG.

Claims (1)

[Scope of Claims] (a) a plurality of capacitive keys arranged at each grid point constituting a matrix; (b) selection means for sequentially selecting keys by scanning rows and columns and switching selection; (c) a detection circuit that detects and outputs a press signal of a selected key; (e) the detection circuit includes an amplifier circuit connected to the output of the selection means; An input voltage holding circuit; a superimposition circuit that superimposes the output of the input voltage holding circuit and the output of the amplifier circuit to input the input voltage holding circuit; and clearing means for clearing the input voltage holding circuit. (f) A capacitive keyboard characterized in that the input voltage holding circuit outputs an output corresponding to a key press over a plurality of scanning cycles.