LCD Module Lens and Lens Modules
  Adjusting the contrast of a character LCD module.
  There are two means of adjusting the contrast: Please refer to the following drawing:
   
1. Internal: J2 short, add the appropriate resister to R7 for contrast control.

2. External: J1 short, R7=0, By adding a VR the contrast can be controlled externally.
Please note the following diagram:

   
  Connecting and powering the backlight.
  There are two means of connecting and powering the backlight. Please refer to the below diagrams:
   
1. PINS 1 & 2 (Vdd & Vss): J3 short, by adding a resistor on R9.

2. PINS 15 & 16: J4 short, by adding a resistor on R8.

NOTE: The brightness can be controlled by the value of R8 or R9.

   
 
Reference table for establishing the relationship between the temperature range, viewing direction and type of polarizer:
  There are two means of connecting and powering the backlight. Please refer to the below diagrams:
   
   
  Differences between a Driver IC, a Controller IC and a Controller/Driver IC:
 
Driver IC:
There are two types of driver IC’s. One is a “common” driver and the other a “segment” driver. Common drivers output signals to create the rows or number of lines while the segment drivers output the necessary signals to create the characters or columns.

Controller IC:
 This IC receives data written in ASCII or JIS code from the MPU and stores this data in RAM. This data is then converted into a serial character pattern and transferred to the LCD driver IC.

Driver/Controller IC:
 This IC is most commonly found in a graphics module. This IC receives data from the MPU and stores it in RAM. This IC accepts commands directly from the MPU for both the common and segment drivers.
   
 
Following is the minimum dot size and pitch on the LCD, the ITO line on the LCD and the elastomer (zebra) connector:
 

Item

Dots or Lines
Gaps
LCD Dots

0.22mm
0.02mm
LCD ITO lines
S=0.075, C=0.08mm
0.03mm
Rubber Connectors

0.025mm
0.025mm
Heat Seal
0.09mm
0.09mm
   
  Advantages and disadvantages of backlight versions:
 
   
  Comparison between TN, STN and FSTN technologies:
 

Item

Contrast Ratio

View Angle
COST
TN

3

3
3
STN
2
2
2
FSTN

1

1
1
   
  Differences between reflective, transflective and transmissive displays?
 
Reflective: Such display includes a diffuser. This layer reflects the light that enters the front of the display. Reflective displays require ambient light for the light source since there is no backlight.

Transflective: As type of backing which is bonded to the rear polarizer. Enables light to pass through the back, as well as reflecting light from the front.

Transmissive: A type of LCD which does not have a reflector or transflector laminated to the rear polarizer. A backlight must be used with this type of LCD configuration. The most common is a transmissive negative image.
   
  Considerations for attaining a 3.0 Volt LCD module:
 
IC: Choose the ICs that can be driven at 3.3V or less. Below is a list of IC’s that can accomplish this requirement:
Controller:

KS0066U 2.7 ~ 5.5V

KS0070B 2.7 ~ 5.5V

HD44780U 2.7 ~ 5.5V

Driver:

KS0065 2.7 ~ 5.5V

KS0063 2.7 ~ 5.5V

SED1181 5.0V min.


LCD panel: The driving voltage for most all LCD panels is above 3.3V. It is necessary to then add a “negative voltage” IC on the PCB of the module or to the customer’s motherboard to raise the voltage. A couple of NV generators is as follows:

NV IC: SCI7661 3X with temperature compensation.

SCI7660 2X, dice font available (at a much less expensive cost).

If a NV IC must be incorporated onto the module PCB, there is apt to be two possible considerations:


1. Tooling cost

2. The PCB is too small to accommodate the NV IC. If there is not sufficient space, a possible
solution would be to replace one controller with a driver, with single controller (such as replacing a
KS0066(U) & KS0065(B) with a KS0070). The per unit cost will be a little greater but it will save
overall space on the PCB and eliminate having to re-tool the PCB.

Some TAB IC’s such as SED1560 series include a power circuit, which can amplify the input
voltage to drive the LCD. In this case it is not necessary to add a NV IC to raise the voltage.

C.Backlight:

CCFL & EL: These backlight options require an inverter. The inverter that is chosen cannot exceed 3.3 Volts.

LED: In an attempt to achieve this 3.3V requirement it is necessary to use an edge-lit LED. Note this
edge-lit LED will still consume a large current.
   
  Reference to Viewing angle:
 
Viewing Angle is the direction by which the display will look best. This is established during the manufacturing process and can not be changed by rotating the polarizer. Viewing direction is specified in terms of a clock position, such as 6:00 & 12:00. Please refer to the following drawing:

   
  Clarification to the term “rainbow” effect:
 
This refers to a red and green circle or rainbow on the LCD glass. The LCD panel under uneven pressure causes this problem from the bezel. This problem is very common in LCD modules and normally it will not affect the performance or the appearance of the display when operational.
   
  Pin assignments for a Character module:
 
Example of a standard 14-pin character module:

PIN 1: Vss

PIN 2: Vdd

PIN 3: Vo

PIN 4: RS

PIN 5: R/W

PIN 6: Enable

PIN 7 ~ 14: DB0 ~ DB7
   
  What is temperature compensation and why is required?
 
A LCD operating voltage varies at different temperatures. The operating voltage must rise as temperature lowers or the contrast will degrade. Conversely, the operating temperature must fall as the temperature rises or the contrast will degrade. For this reason it is often a requirement, with graphics modules, to control the input voltage accordingly. The temperature compensation circuit is the circuit that controls the input voltage as the temperature changes. This temperature compensation circuit can be located on the LCD module or on the customer’s motherboard.
   
  Troubleshooting an LED backlit module in which the display is turning dark:
 
This problem is more than likely caused by the temperature rise from the LED backlight. In this case the LED backlight has consumed too much of the power. When the temperature rises, the VLCD requirements lower causing the input voltage to be too high. The result is a poor contrast and the display becoming too dark. The solution would be to lower the power consumption of the LED. This can be accomplished by raising the value of R8 or R9 to reduce the current to the LED backlight.
   
  Controlling the LED backlight on a 14-pin module:
 
Short J2, the Vdd is controlling the input to the LED backlight. In addition, it is necessary to place a current limiting resistor to lower the voltage from 5V to 4.2V.

Note: If the LED is drawing too much current it may cause the Vdd – Vo to lower and the contrast to become poor. If this should occur increasing the value of R9 should decrease the current draw to the LED backlight or another approach would be to increase the voltage input to the LCD by decreasing the value of R7.
   
  Brief description of various controller IC’s:
 

Font Number

IC Number

Temp. Range
Content
SO

KS0066

Wide
English/Japanese
EA
SED1278
Normal
English/Japanese
S5

KS0066

Wide

English/Europe
EB

SED1278

Normal
English/Europe
   
 
Examples of the current consumption of an LED backlit, EL backlit and the LCD for the following modules:
 

Products

LCM

LED
EL
PC1602-F

1.3mA

120mA
3.26mA
PC2002-B

1.8mA
200mA
5.3mA
PC2004-A

1.8mA

260mA
7.2mA
PC4004-A

2.2mA

440mA
7.5mA
   
  Following is the Vop range for a Character and Graphics LCD module:
 

LCD Type

Vop for N.T.

Vop for W.T.
Character

4.2 ~ 4.8V

5 ~ 9V
Graphic

5.5 ~ 26V
6 ~ 28V

Note: N.T. = normal temperature

W.T.= wide temperature