DEVICE FOR KEY INPUT

摘要

A key input device is provided to discriminate key codes by including a capacitor repeatedly charged/discharged by key input and using a charging/discharging time of the capacitor. A plurality of key switches(SWn) have a switch contact point and a switch contact piece opening/closing the contact point. The plurality of key resistors(Rn) are connected to each key switch in serial and have a different resistance. The capacitor(C1) is charged/discharged by an external reference clock and outputs pulse volatile with a different width according to the key resistance if each key switch is turned on. A microcomputer(10) generates the reference clock and determines the key code corresponding to the width by measuring the pulse voltage received from the capacitor. The microcomputer includes a memory(12) storing key code data corresponding to the width of the pulse voltage and a controller(11). The controller measures the width of the received pulse voltage, checks the key code corresponding to the measured width, and outputs the control signal corresponding to the checked key code to the outside.