Little Board™/486e Technical Manual
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 display. Do not confuse this with a backlight that illuminates 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 attachment of a remote potentiometer.
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
| Rb |
| Ra |
External Contrast | Ground |
Control |
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 = | 270 |
| - 12 | Rb = | 270 | - 12 - |
|
|
| ||||
(Vee max / | 1.5) | (Vee min / 1.5) |
