| 摘要 |
PURPOSE:To detect a key selecting point by a simple circuit even when the number of key selection points is large, by connecting resistance groups to longitudinal and lateral conductor lines of a key matrix, and utilizing voltage drops across the resistance the resistance groups due to key operation. CONSTITUTION:The longitudinal and lateral conductors LC1-LCn of the keyboard matrix 20 are connected to the resistor groups VR1, R0-Rn-1, and VR2, and VR'1, R'0-R'n-1, and VR'2, and those resistance groups are connected to a constant voltage +5V and the ground through changeover switches 21 and 22, respectively. When a desired intersection Xii in the matrix 20 is depressed, a divided voltage in the resistance corresponding to the point Xii is A/D-converted 24 through some resistance groups VR'1-VR'2 and the side of the contact (b) of a relay 23 and then supplied to a CPU through an input interface IF25. Then, relays 21-23 are changed over by a relay driving circuit 27 and a divided voltage in the VR'1-VR'2 is A/D-converted 24 through some of the VR1-VR2 and the contact (m) of the relay 23 and inputted to the CPU through the IF25. The CPU discriminates the position of the Xii by those two voltages. |
