Importance

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Abstract

A key matrix circuit has a switching circuit with a first terminal and a second terminal that are switched on and off by pressing a selection key of a plurality of selection keys arranged in an N-row-by-M-column matrix, thereby making connection to a common ground circuit when a selection key is pressed. The key matrix circuit has a first voltage-dividing circuit connected between a connection circuit that connects the first terminals of the first row and a fixed power supply voltage, and a second voltage-dividing circuit connected between a connection circuit that connects the second terminals of the first column and the fixed power supply voltage, the connection points between resistances to of the first voltage-dividing circuit being connected to the connection circuits connected to the first terminals of the other rows, and the connection points between resistances of the second voltage-dividing circuit being connected to the connection circuits of the other rows. An output voltage at the connection point between the first voltage-dividing circuit and an output voltage at the connection point between the second voltage-dividing circuit are input to a microcomputer circuit. Based on combinations of the voltage levels, the microcomputer circuit references a table prepared beforehand, so as to recognize what selection key has been pressed.

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First Claim