| 摘要 |
PURPOSE:To adjust optical brightness for illumination and to make a reading signal level constant in accordance with a card surface by detecting the white level paek value of an optical reading signal and controlling brightness of a light source for illumination in accordance with the detected value. CONSTITUTION:The output of a reading sensor 1 is given through an amplifier circuit 2 to a white level peak hold circuit 3. This output and the output of reference voltage source 5 for illumination are added by an adder circuit 4 and the sum is given through an amplifier circuit 6 to an electric power source 7 for illumination. Thus, even when the level of the reading signal of the reading sensor 1 changes, the light source 7 for illumination preserves brightness in accordance with a maximum value in a fluctuation level, and when the level of the reading signal becomes larger, brightness is made smaller by increased amount. |
