Ampro Corporation P5X manual J4 Pin J3 Pin Description, Attaching an External Contrast Control

		Little Board/P5x Technical Manual
	Table 2– 34. LCD Bias Supply Option Connector (J4)
J4 Pin	J3 Pin	Description
1		Ground
2		+5V to the Vee Supply Option board
4		Ground
6	38	Enable Vee — TTL control signal, driven by the VGA
		controller chip
8		Ground
11	46	Vee Output, to panel
12	47	Contrast adjustment — analog control signal

Selecting Vee Polarity

Most LCD displays require a Vee supply of between 15V and 35V. Some panels need a negative supply, and some a positive supply. The LCD Bias Supply Option provides a jumper for selecting the Vee output polarity. To select the polarity for the panel you will be using, set the jumper on W1 (on the LCD Bias Supply board, not on the Little Board/P5x) as follows:

!	Negative Vee	W1-1/2
!	Positive Vee	W1-2/3

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, which illuminates the screen using one or more fluorescent tubes. Backlights generally require a high voltage AC supply.)

An on-board control (R1) on the LCD Bias Supply board 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 a 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.

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