| 摘要 |
<p>PURPOSE:To eliminate necessity of adjusting luminous intensity every time by providing a photodetector in a coordinate indicator and driving a light source according to output of the photodetector. CONSTITUTION:When the coordinate indicator 1 is within effective range of reading on a sense line plate 14, a valid signal (a) is outputted from a CPU19, and a switching circuit 7 is made on and a voltage signal (d) is outputted from a comparator circuit 6 to a dimming circuit 9. When a drawing is placed on the plate 14, current from the photodetector 4 is diminished according to transmissivity of the paper, and accordingly a voltage signal (b) from an amplifier circuit 5 is also lowered. At this time, the voltage signal (d) is supplied to the circuit 9 according to the difference between a voltage signal (c) from a luminous intensity setting section 8 and the signal (b). Then, the signal (c) and signal (d) are added and inputted to the circuit 9 and works to raise the luminous intensity of the light source 10. Accordingly, brightness through a reading medium on the plate 14 can be maintained at set brightness without depending on presence or absence of drawing, quality of the paper etc.</p> |
