Toshiba e-STUDIO281c Service Manual page 160

About reflection type photosensor
The reflection type photosensor is comprised of an infrared light emitting diode and a phototransistor. It
uses pulse modulation to detect an original.
Original
8 µsec
130 µsec LED Phototransistor
Fig. 6-18
The light emitting diode is driven by a pulse having a 130 µsec. cycle and an 8 µsec. ON time. When
the phototransistor receives the same signal as this pulse, it is determined that there is an original. The
pulse modulation is performed inside the reflection type phototransistor.
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