Canon NP6085 Service Manual page 207

3. LCD Contrast Automatic Adjustment
The control panel controller PCB is equipped
with a function which automatically controls the
LCD contrast.
A thermistor (TH911) is used on the control
panel controller PBC to monitor the temperature
of the control panel. The changes in the resis-
tance detected by the changes in the temperature
monitored by the thermistor are used to vary the
voltage supplied to the LCD, thereby maintaining
the LCD contrast at all times.
The LCD contrast need not be adjusted since
it is adjusted at time of shipment from the factory.
0V
Thermistor
(TH911)
Vo
VR911
DC/DC
converter
-24V
Vo: Supply voltage to LCD.
Figure 3-503
When the temperature near the control panel
increases, the resistance to the thermistor
decreases, increasing the supply voltage (V
the LCD.
When the temperature near the control panel
decreases, the resistance to the thermistor
increases, decreasing the supply voltage (V
the LCD.
COPYRIGHT © 1996 CANON INC.
LCD
+5V
) to
O
) to
O
CANON NP6085 REV.0 JULY 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)
3. OPERATIONS AND TIMING
4. Touch Switch Input
The keys on the touch switch panel and the
control panel controller PCB are connected as
shown in Figure 3-502. The touch switch panel
consists of two glass sheets coated with transpar-
ent conducting membranes bonded with spacers
in between; it has keys in 15 columns and 20 rows
in a specific pattern.
When the surface of the top glass sheet is
pressed, the contact between the two sheets will
cause electrical continuity.
This causes a pair of electrodes to have elec-
trical continuity, allowing detection of X/Y coordi-
nates as in the case of a common key matrix.
(The correspondence between the key scan sig-
nal from the control panel controller circuit and the
input signal to the control panel controller circuit
enables the control panel controller PCB to iden-
tify which key has been pressed.)
Spacer
Electrode
Electrode Glass sheet
Figure 3-504
Glass sheet
3-149