2A3/4
2-3-18
(3) Operating principle of reflective photosensors PPSENS1, PPSENS2,
PPSENS3 and PESENS
IC9.4
R42
98
IC5.3
R43
PDMPCB
I/FPCB
R15
6
76
5
CPU
IC7
5
Off
On
+5 V DC
R44
Off
On
Phototransistor
LED
Q14
PPSENS 3
Figure 2-3-14 Reflective photosensor (PPSENS3) circuit
The following is the operating principle of paper path sensor 3 (PPSENS3). Paper path
sensors 1 and 2 (PPSENS1, PPSENS2) and the paper empty sensor (PESENS)
operate in the same manner.
Pulsating signal from pin 5 of the CPU IC7 turns Q14 on and off, causing the LED on
the sensor PCB to flash. When the flashing LED light reflects on the paper, the
phototransistor turns on and off. The on/off signal is then inverted by IC9.4 and the
paper presence signal (pulse) is input at pin 76 of the CPU IC7.
If there is no paper, the phototransistor remains off and 5 V DC is input at pin 76 of the
CPU IC7.
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