| 摘要 |
PROBLEM TO BE SOLVED: To enable a key switch circuit to discriminate whether the circuit itself is connected or not, not depending on increasing the number of input ports for a CPU or the like in electronic equipment or increasing the number of connection lines to the electronic equipment. SOLUTION: Short circuits are provided by plural resistors R1 to R4 and plural key switches S1 to S4. A hold circuit consisting of a resistor 8 and a holding switch 9 is connected to the key circuit 2. Which key switch is depressed is discriminated by an output voltage change outputted from the circuit 2 to the input port Vin of electronic equipment 7. Fixed voltages corresponding to the ON/OFF of the switch 9 are applied to the input port Vin of the equipment 7, and the depression/non-depression of each of the key switches S1 to S4 and a holding/non-holding state are selected by discriminating the voltage outputted to the input port Vin.
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