Keyboard apparatus

• US 4,772,874 A
• Filed: 12/07/1987
• Issued: 09/20/1988
• Est. Priority Date: 02/29/1984
• Status: Expired due to Term

• Current Assignee: Topre Corporation
• Original Assignee: Topre Corporation
• Inventors: Hasegawa, Hiroshi
• Primary Examiner(s): Brigance, Gerald L.
• Assistant Examiner(s): FATAHI YAR, MAHMOUD
• Application Number:
  US07/129,901
• Time in Patent Office: 288 Days
• Field of Search: 340/365 S, 340/365 R, 340/365 C, 340/365 E, 364/189, 364/700, 364/709, 400/473, 400/479, 400/485
• US Class Current: 341/26
• CPC Class Codes: G06F 3/023 Arrangements for converting discrete items of information into a coded form, e.g. arrangements for interpreting keyboard generated codes as alphanumeric codes, operand codes or instruction codes
• CPC Class Codes: H03M 11/20 Dynamic coding, i.e. by key scanning H03M11/26 takes precedence

Abstract

A capacitive keyboard apparatus including a plurality of keys and a matrix of capacitive switches arranged in columns and rows and connected to the keys, respectively, wherein first and second drive signals sweep the columns of switches and first and second matrix output signals are generated from the rows of switches as the result of first and second drive signal supplied, provided that any key has been depressed during the sweeping. The first and second matrix output signals are convertred to first and second logic signals, respectively, each of which has a pulse width proportional to how deeply the key has been depressed. When the first logic signal has a pulse width broader than a first predetermined width, the second drive signal sweeps the columns of switches. It is determined that the key has been depressed and a key-code corresponding to the depressed key is output, when the second logic signal has a pulse width broader than a second predetermined width and when the second keys during the sweeping by the first and second drive signals are identical.

Claims

1. A capacitive keyboard apparatus comprising:

a plurality of capacitive switches, each being coupled to a key and having an electrostatic capacitance varied in proportion to the depth to which the key has been depressed;

a switch matrix including said capacitive switches arranged in columns and rows;

drive signal supplying means connected to the columns of said switch matrix for sequentially supplying a drive signal to the columns, wherein a matrix output signal having a pulse width varied in proportion to the depth, to which any key of said switch matrix has been depressed, is generated from said drive signal and supplied to the row to which the depressed key is connected;

selection means connected to the rows of said switch matrix for sequentially selecting the rows, thereby to select the matrix output signals which have been generated and supplied to the rows;

signal converting means connected to said selection means for converting each matrix output signal selected by said selection means into a logic signal whose pulse width is proportional to the pulse width of the matrix output signal;

first judging means connected to said signal converting means for receiving the logic signal and determining whether or not the pulse width of the logic signal is broader than a first predetermined width which corresponds to the width to be determined that the key has been depressed;

second judging means connected to said signal converting means for receiving the logic signal and determining whether or not the pulse width of the logic signal is broader than a second predetermined width which is narrower than the first predetermined width; and

control means connected to said drive signal supplying means, said selection means, said first judging means, and said second judging means, for controlling said driving signal supplying means thereby to sequentially supply a first drive signal to the columns of said switch matrix, for controlling said selection means thereby to select the matrix output signal generated by depressing any key of said switch matrix in accordance with the first drive signal, for controlling said driving signal supplying means thereby to sequentially supply a second drive signal to the columns of said switch matrix when said first judging means determines that the logic signal generated from the matrix output signal, which has been generated by depressing the key of said switch matrix in accordance with the first drive signal, has a pulse width broader than the first predetermined width, for controlling said selection means thereby to select the matrix output signal generated by depressing the key of said switch matrix in accordance with the second drive signal, for determining in accordance with the first and second logic signals, whether the keys depressed are identical or not when said second judging means determines that the logic signal, generated in accordance with the second drive signal, has a pulse width broader than the second predetermined width, and for outputting a key code corresponding to these keys when these keys are determined to be identical.

2. The capacitive keyboard apparatus according to claim 1, wherein said control means causes said drive signal supplying means and said selection means to sweep all columns and all rows of said key switch for a second time in accordance with the second drive signal after said drive signal supplying means and said selection means have swept all columns and all rows of said switch for a first time in accordance with the first drive signal.

3. The capacitive keyboard apparatus according to claim 2, wherein said first judging means comprises first delay means for outputting a signal having a predetermined pulse width upon lapse of a first period of time after any logic signal has been generated and first logic operation means for performing a logic operation on the signal output from said first delay means and the logic signal and supplying the results of the logic operation to said control means;

and said second judging means comprises second delay means for outputting a signal having a predetermined pulse width upon lapse of a second period of time after any logic signal has been generated, said second period of time being shorter than the first period of time, and second logic operation means for performing a logic operation on the signal output from said second delay means and the logic signal and supplying the results of the logic operation to said control means.

4. The capacitive keyboard apparatus according to claim 3, wherein said control means supplies a control signal to said first and second logic operation means, said first logic operation means does not output the results of the logic operation while said drive signal supplying means is supplying the second drive signal, and said second logic operation means does not output the results of the logic operation while said drive signal supplying means is supplying the first drive signal.

5. The capacitive keyboard apparatus according to claim 4, wherein said first logic operation means performs an AND operation on the signal output from said first delay means, the logic signal and the control signal, and said second logic operation means performs an AND operation on the signal output from said second delay means, the logic signal and the control signal.

6. The capacitive keyboard apparatus according to claim 5, wherein said first period of time is 2.5 to 3 microseconds, and said second period of time is about 1 microseconds.

7. The capacitive keyboard apparatus according to claim 1, wherein when said first judging means determined that the logic signal which is generated from the matrix output signal corresponding to said first signal and is converted at said signal converting means has a pulse width broader than the first predetermined width, said control means causes said drive signal supplying means to supply the second drive signal to the column of said switch matrix which has received the matrix output signal corresponding to the first drive signal, and causes said selection means to select the row of said switch matrix which has received the matrix output signal corresponding to the first drive signal.

8. The capacitive keyboard apparatus according to claim 7, wherein said first judging means comprises first delay means for outputting a signal having a predetermined pulse width upon lapse of a first period of time after any logic signal has been generated, and first logic operation means for performing a logic operation on the signal output from said first delay means and the logic signal, and supplying the results of the logic operation to said control means;

and said second judging means comprises second delay means for outputting a signal having a predetermiend pulse width upon lapse of a second period of time after any logic signal has been generated, said second period of time being shorter than the first period of time, and second logic operation means for performing a logic operation on the signal output from said second delay means and the logic signal, and supplying the results of the logic operation to said control means.

9. The capacitive keyboard apparatus according to claim 8, wherein said control means supplies a control signal to said first and second logic operation means, said first logic operation means does not output the results of the logic operation while said drive signal supplying means is supplying the second drive signal, and said second logic operation means does not output the results of the logic operation while said drive signal supplying means is supplying the first drive signal.

10. The capacitive keyboard apparatus according to claim 9, wherein said first logic operation means performs and AND operation on the signal output from said first delay means, the logic signal and the control signal, and said second logic operation means performs an AND operation on the signal output from said second delay means, the logic signal and the control signal.

11. The capacitive keyboard apparatus according to claim 10, wherein said first period of time is 2.5 to 3 microseconds, and said second period of time is about 1 microseconds.

12. The capactive keyboard apparatus according to claim 7, wherein said control means outputs a first sampling pulse to said first judging means upon lapse of a first period of time after the first drive signal has been generated, and outputs a second sampling pulse to said second judging means upon lapse of a second period of time after the second drive signal has been generated, and said second period of time being shorter than the first period of time, said first judging means performs an AND operation on the first sampling pulse and the logic signal, and supplying the results of the AND operation to said control means, and said second judging means performs an AND operation on the second sampling pulse and the logic signal, and supplying the results of the AND operation to the control means.

13. The capacitive keyboard apparatus according to claim 12, wherein said control means outputs the first sampling pulse while said first drive signal is being generated, and outputs the second sampling pulse while said second drive signal is being generated.

14. The capacitive keyboard apparatus according to claim 13, wherein said first period of time is 2.5 to 3 microseconds, and said second period of time is about 1 microseconds.