AR-FN2 (serv.man10). ARFN2 Service Manual-Circuit Descriptions - Sharp Copying Equipment Service Manual (repair manual). Page 10

SHPS is the micro switch used to detect the staple stand-by position. It is ON when in the home position. 
The signal is inputted to the CPU (IC 9-76 pin) through the noise filter of R12 and C16 and the schmidt trigger (IC 1-2). 
Logic of signals inputted to the CPU: Home position not detected 

®

 H, Home position detected 

®

 L

NNES is the reflection-type sensor which detects staple near end. It integrates the LED and the photo transistor. 
No reflection at near end. 
The signal is inputted to CPU (IC 9-63 pin) through the noise filter of R18 and C52. DA1 is the protection diode which protects the +5V line voltage
from deflection. 
Since this signal is analog, staple empty is detected by the threshold value of 2.75V. 
Logic of the signal inputted to the CPU: Staple presence 

®

 2.75V or less, Staple empty 

®

 2.75V or above

STP is used to detect the connection of the stapler unit. 
When the connecter is connected, the signal is connected to GND and detected. 
The signal is inputted to CPU (IC 9-19 pin) through the noise filter of R7 and C10. R59 is the pull-up resistor. 

Staple home position sensor input circuit

Staple home position
sensor
(SHPS)

Staple near end sensor
(NNES)

Stapler near end sensor input circuit

Stapler presence sensor input circuit

Stapler presence sensor
(STP)

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