PURPOSE: To obtain an accurate coordinates signal, by controlling the light quantity of the light source automatically on a basis of the output signal of the optical position detector.
CONSTITUTION: Light emitting diode 5 is lit by the driving current transmitted from power source circuit 4, and the light is projected to face 18 of optical position detector 1 by optical lens 6. Signals at position signal terminals 15 and 16 of detector 1 are input to amplifiers 24 and 25 constituting the substracting circuit and are amplified and are converted to voltages and are input to terminal 27 for the signal to be subtracted and terminal 28 for the subtracting signal of subtractor 26, and the signal of their difference is transmitted from output terminal 23 of subtractor 26. The voltage transmitted from output terminal 46 of comparator 42 lights emitting diode 5; and when the light of diode 5 is input to detector 1 through optical lens 6, the current transmitted from common terminal 17 is amplified, and the voltage which is applied to inversion input terminal 44 of comparator 42 is equal to the reference voltage.
YAMAMOTO AKINAGA
KURASAWA KAZUO
