Segment LCD (Segment LCD) is the simplest and most commonly used type of liquid crystal display. The digital/stroke displays on electronic scales, calculators, thermostats, and small household appliance panels are basically segment LCDs.

Ⅰ. What is a segment LCD?

Segment code LCDs are not dot matrix screens; instead, they have fixed "stroke segments". By controlling the on/off state of each segment, they can form numbers, letters, and simple symbols.
The most typical one is the 8-character 7-segment display: a, b, c, d, e, f, g, plus the decimal point dp.

【Schematic diagram：】

┌── a ──┐
 f        b
 ├── g ──┤
 e        c
 └── d ──┘dp（decimal point）

By controlling any several segments to light up, numbers 0 to 9 can be displayed.

II. Core Structure

A segment LCD is composed of these layers:
 1. Two pieces of glass, one on top and one at the bottom
 2. Transparent ITO electrode (segment electrode, common electrode COM)
 3. Liquid crystal layer (mainly TN/HTN/STN/FSTN/VA types)
 4. Polarizers (upper polarizer, lower polarizer
 5. Sealed frame and conductive adhesive / pins

III. Working Principle

An electric field is used to change the rotation direction of liquid crystal molecules, controlling whether light can pass through two polarizers to achieve "segment lighting/segment extinguishing".
 When not powered on: The display is on.
 • Liquid crystal molecules rotate naturally
 • Light passes through the lower polarizer → is twisted by the liquid crystal → passes through the upper polarizer
 • Visually: This section is displayed as bright (black text on a white background or white text on a black background)
 When an electric field is applied: shows black (not lit)
 • Liquid crystal molecules are straightened by the electric field and no longer rotate
 • After passing through the lower polarizer, the direction of the light remains unchanged and is blocked by the upper polarizer.
 • Visually: This section turns black and is not displayed

Ⅳ. Driving Methods: Static Driving & Dynamic Multiplex Driving

１. Static drive
 • Each segment has an independent wire + a common pole COM
 • Advantages: clear, high contrast
 • Disadvantage: If there are many segments, there will be an extremely large number of pins.

2. Dynamic Multiplex Drive (commonly used)
 • Divide the paragraph into multiple groups COM
 • Row scanning and column selection, quickly lighting up in turns
 • Advantages: few pins, low cost
 • Segment LCDs almost all use this kind.

V. Characteristics of Segment LCD

 • Simple structure and extremely low cost
 • Ultra-low power consumption (μA level, suitable for battery power supply)
 • High contrast, visible in sunlight
 • Can only display fixed digits, strokes, and fixed icons
 • Slow refresh rate, cannot display animations or pictures

Ⅵ.Typical Applications

• Thermostats, electricity meters, water meters
 • Small home appliances: rice cookers, fans, alarm clocks
 • Simple in-vehicle meters, toy displays
 • Electronic scales, calculators