Ampro Corporation LITTLE BOARD P5X - Manual (Page 62)

2–44
To use an external potentiometer, remove the jumper from W2, and connect a circuit as shown in
Figure 2– 4 between J3-47 and ground.
Ra
Rb
Ground
J3-47
External Contrast
Control
Figure 2– 4. 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 the
contrast adjustment. Use the following formulae to calculate the resistor values (in K Ohms).
270
Ra = - 12
(Vee max/1.5) - 1
270
Rb = - 12 - Ra
(Vee min/1.5) - 1
Example:
Suppose the following values are shown in the panel’s data sheet:
Vee Max = 24 V
Vee min = 20 V
Calculate the required resistor values as follows:
Ra = (270 / ((24 / 1.5) - 1)) -12
Ra = 6K Ω
Rb = (270 / ((20 / 1.5) - 1)) -12 - 6
Rb = 3.9K Ω
In this example, you would use 6K Ω for Ra and a 3.9K Ω potentiometer for Rb.
Connecting a CRT (J5)
Analog video signals from the video controller appear on a 10-pin dual-row header, J5. These
signals are compatible with the standard video monitors commonly used with desktop PCs.
Specifications for compatible monitors are provided in Chapter 3, Technical Specifications.
Normally, signals from J5 are connected to a standard DB-15 video connector by a “transition
cable,” made from a ribbon cable connectors and a short length of 10-wire ribbon cable. A transition
cable can connect the video signals to a bulkhead-mounted DB-15 connector, allowing any standard
CRT to be easily connected using a standard monitor video cable.
+5V power, protected by fuse F3, can supply power to an external device, such as an NTSC Video
adapter module.