MR-2012 CIRCUIT DESCRIPTION
5 - 2
October 2000 © TOSHIBA TEC
5.3 ADF Read Sensor Input Circuit
The ADF read sensor input circuit is installed on the scanner PWA. The ADF PWA only allows the signal
only to pass through. Therefore, this section describes the ADF read sensor input circuit on the scanner
PWA.
The ADF read sensor is a mirror reflective type sensor and consists of a pair of a infrared LED and a PTr
(phototransistor) each having an optical axis in the same direction. A mirror is provided on an extended line
of the optical axis of the sensor. When there is no document between the sensor and the mirror, an infrared
light emitted from the LED is reflected to PTr at high reflectance. When there is a document between them,
the emission to the mirror and the reflected light from the mirror are obstructed by the document so that the
reflected light incident on PTr becomes extremely low. When a quantity of light incident on PTr is large (no
document present), photoelectric current flowing through PTr increases and a drop in voltage due to R17
causes the voltage at pin 6 of IC8 to rise.
IC8 is a comparator which compares the reference voltage input to pin 5 (non-inverting input) with the signal
voltage at pin 6 (inverting input). When the voltage at pin 6 is higher, the output (pin 7 of IC8) turns to “Low”
level. Conversely, when a quantity of light incident on PTr is small (a document present), the voltage at pin
6 of IC8 becomes low and as a result pin 7 of IC8 turns to “High” level.
An automatic sensitivity adjusting function is also provided to control variations in sensor sensitivity.
When the sensor sensitivity adjust mode is selected, the automatic adjustment measures the output
voltage (analog value) of PTr at the A-D input terminal on the scanner side, changes the D-A output voltage
on the scanner side to make the PTr output voltage become the required voltage, and adjusts the LED
current through the voltage-current conversion circuit consisting of IC7, Q2, R20, etc.
+5V
R17
R18
POS_DA
REF_DA
IPOS
POS_AD
R22
R23
C16
C17
C19
IC7
5
6
7
Q2
+
-
IC7
3
2
1
+
-
IC8
5
6
7
+
-
R19
ADF
Scanner
ADF 05-03-01
