| 摘要 |
PROBLEM TO BE SOLVED: To compensate the variation in luminance of light emitting elements in a key sensor measuring key positions K based on the output signals Sa of concerned light receiving elements by providing shutters shielding intervals between the light emitting elements and the light receiving elements to keys. SOLUTION: LEDs 224-1 to 224-12 are cyclically set in ON states and currents to be supplied to them are determined in a current control circuit 150. A CPU 201 supplies optimal currents to respective LEDs by setting ON/-OFF states of transistors 103, 104 in accordance with LEDs to be lit. Moreover, lights radiated from the LEDs are received by photodiodes 225-1 to 225-8 and the CPU 201 determines the ON/OFF states of the transistors 103, 104 by monitoring these levels. |
