| 摘要 |
PURPOSE:To make the average light receiving quantity of a reflected light of an optical card Ca constant. CONSTITUTION:A projected light of an optical card is detected by a photodiode 20. A maximum value of the received light detection signals of the photodiode 20 is obtained and control data are outputted from a CPU 25 so as to make the difference between the maximum value and the target value stored in the CPU 25 becomes less. The control data are analog transformed, given to a driving current output circuit 27 and the radiated light intensity of a light emitting diode 16 is adjusted. The meximum value of the received light detection signals of the photodiode 20 and the target value are made coincident and the average received light quantity of the photodiode 20 becomes constant. |
