Paper Sensor - Brother MP-21C Service Manual

2.3.4

Paper Sensor

The photo type sensor is contained on the Main PCB. The movable part of the
mechanism detects if there is paper or not and turns the sensor on and off. When light is
transmitted, there is no paper.
The CH1 level of the sensor output is less than 2.5V without paper and 2.5V or more with
paper present.
<Without paper>
Main PCB
CPU Pin
(
)
Fig. 2.8
Movable tip
PH1
Fig. 2.9
II-7
CPU
(
<With paper>
Movable tip
PH1
Main PCB
Pin
)