Panasonic KX-FB423CN Manual page 350

7.6.2. DOCUMENT SENSOR...."CHECK DOCUMENT" AND PAPER FEED
SENSOR...."REMOVE DOCUMENT"
These Sensors detect whether or not a document is in place. When a document is detected, the shelter plate let the sensor light
pass through, the photo-transistor turns ON, and the input signal of IC501-22pin /IC501-23pin becomes a low level.
When there is no document, the shelter plate shuts off the sensor light, the photo-transistor turns OFF, and the input signal of
IC501-22pin /IC501-23pin becomes a high level.
Document Sensor
Paper Feed Sensor
Photo transistor
No Document
Document Set
Photo transistor
No Read Position
Read Position
Signal(IC501-22pin)
OFF High level
ON Low level
Signal(IC501-23pin)
OFF High level
ON Low level
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KX-FB423CN