Ampro Corporation 486E manual =-

Little Board™/486e Technical Manual
2–40
Note
Incorrect Vee polarity or voltage can damage an LCD panel. Set the
polarity and voltage on the Vee supply before connecting the LCD
panel.
Attaching an External Contrast Control
Vee controls the contrast of the LCD disp lay. Do n ot co nfuse thi s wi th a backl igh t tha t illu min ate s
the screen using one or more fluorescent tubes. Backlights generally require a high voltage AC
supply.
An onboard control (R1) allows you to set the precise Vee voltage for the contrast you require.
However, you may want to provide a more accessible Vee control so that the user can set the
display contrast to accommodate various ambient lighting conditions. The board provides a jumper
and control signal to allow the attachmen t of a r emo te p oten tiome ter .
To use the contrast potentiometer on the LCD Bias Supply board, install a jumper on W2 (on the
LCD Bias Supply board).
To use an external potentiometer, remove the jumper from W2, and attach the circuit shown in
Figure 2–10 between J3-47 and ground.
Figure 2–10. External Contrast Adjustment for LCD Panels
Select Ra and Rb to provide the appropriate voltage range adjustment for the LCD panel you are
using. Consult your panel’s technical literature for the range of voltages you need to supply for
contrast adjustment. Use the following formulae to calculate the resistor values (in K Ohms).
Ra Rb
Ground
J3-47
External Contrast
Control
270
(Vee max / 1.5) -1
Ra 12
=-
270
(Vee min / 1.5) -1
Rb 12
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