Engineering Design Guide for Segment LCD Glass Displays
This article is written as a technical introduction guide for segment LCD glass displays with the goal being to remove sales and marketing hype and replace it with an engineering point of view. This information will be technical in nature.
Segment LCD Names
There are several different names for the type of LCD you see pictured below. These include: segment display, static LCD, LCD glass only, segment LCD glass displays, and 7 segment display. Different terminology but basically the same technology.
A segment LCD glass is a LCD module that displays seven segments or icons when an electrical field is applied across the glass.
Other options of a segment LCD glass include the type of interface or bus such as: multiplex (4:1 mux being the most popular), I2C, SPI and even a parallel (4 bit or 8 bit), although this last interface is rare.
A static display [also referred to as a direct drive LCD] is a unique case of a segment display where there is one pin (connection) for every one segment. Direct drive since each segment is either ON or OFF 100% of the time and there is no duty cycle. Direct drive static displays offer a slightly sharper contrast than any other drive method and they also perform better at colder temperatures.
Segment LCD Glass Construction
Segment is the simplest of all the LCD display technologies on the market and it is probably one of the oldest LCD technologies.
The LCD is built when two pieces of glass are cut to the exact size, an ITO coating is applied to the glass and then the segments/icons are burned into the glass.
The two treated pieces of glass are then ‘sandwiched’ together with an adhesive; the void between the two layers is filled with a nematic fluid such as TN, STN, FSTN, and UWVD. The new UWVD fluid is becoming more and more popular.
When an electrical field is applied across the glass, the liquid molecules will rotate to block light (positive mode) or to allow light to pass through (negative mode).
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