Patent ID: 6509846
Filing Date: 2003-01-21
Classification: H03M

Abstract:
A key matrix circuit comprising:a keyboard comprising a plurality of selection keys arranged in an N-row-by-M-column matrix; a board comprising switching circuits having a first terminal and a second terminal that are connected to a common ground circuit when a corresponding selection key is pressed, the first terminals of each switching circuit, corresponding to said selected key in a row direction being connected to a first connection circuit in units of rows, and the second terminals of each switching circuit, corresponding to a selected key in a column direction being connected to a second connection circuit in units of columns; an output circuit wherein a fixed-voltage power supply and one circuit of said first connection circuits are connected by a first voltage-dividing circuit formed by a series connection of N resistances, with other first connection circuits connected to points between other said resistances of said first voltage-dividing circuit, a first output point being a resistance connection point of said first connection circuit via one resistance from said fixed-voltage power supply, and wherein a fixed-voltage power supply and one circuit of the second connection circuits are connected by a second voltage-dividing circuit formed by a series connection of M resistances, with other second connection circuits connected to points between other said resistances of said second voltage-dividing circuit, a second output point being a resistance connection point of the second connection circuit via one resistance from the fixed-voltage power supply; and a microcomputer circuit which A/D converts and captures the voltages at said first output point and said second output point of said output circuit and, using a data table, into which are stored identification data and control commands corresponding to combinations of voltage levels that the first output point can take and voltage levels that the second output point can take, these combinations being related to each selection key, performs recognition of a pressed selection key and execution of corresponding control.