| 摘要 |
PURPOSE:To confirm a depressed switch by outputting an analog voltage corresponding to a key switch from a voltage generating part and discriminating whether a single switch or plural switches are depressed, by varying the resistance value of a corresponding variable resistance circuit to a value corresponding to the switch by depressing either key switch. CONSTITUTION:A great number of switches SW1-SW6 and resistors R1-R6 connected to the switches SW1-SW6 in series respectively are provided on a keyboard K, and the serial circuit is connected in parallel between the terminals 2 and 3 of both ends of the variable resistance circuit 1. The A/D converter 5 of the main body M of a key input device is connected to the terminals 2 and 3 of the circuit 1, and a constant voltage terminal 4 connected to a constant voltage power source VC is connected to the VREF of the converter 5. Also, a reference resistor R8 which generates an analog voltage corresponding to the resistance value based on the voltage division ratio of the resistors R1-R6 of the circuit 1 is connected to a VINV/D. Then, it is possible to miniaturize the key input device and to easily identify depressed key switches SW1-SW6.
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