Segment LCD Design: From Artwork Sketch to COM/SEG Pin Map

By the SuccessLCD Engineering Team · Updated November 3, 2026

A custom segment LCD is designed from the pin count backwards, not from the artwork forwards. Every segment sits where one COM electrode crosses one SEG line, so a glass with C commons and S segment lines can carry at most C × S segments on C + S pins. The work is to fit the artwork into that matrix, route the ITO so no trace makes a stray “ghost” segment, and leave the glass margins the factory needs. Do that before anyone polishes the artwork, because changing a pin map after tooling means new glass.

Below is the order we work in when a sketch arrives, with the numbers from our own catalogue references where they help.

Count first, then pick the duty

List every element that must switch on and off on its own: each digit segment, each decimal point, colons, icons, bar-graph steps and unit symbols. Anything that never changes, such as a printed scale, a logo or fixed unit text, does not need an electrode. It can be printed on the polarizer, the cover lens or the bezel, and it costs no pins.

Fewer pins are not free. As the duty goes up, the voltage difference between an “on” and an “off” segment shrinks, so contrast, viewing angle and temperature margin drop. Static drive gives the best of all three and is still used where a display must stay crisp at a wide angle, such as our four-digit static S3960D (HTN, 4.0 V, 64 Hz). Many instrument displays run at 1/4 duty and 1/3 bias, which is what our pin-type references S04805D, S04778D, S04799D and S04802D use, all at 5.0 V and 64 Hz. Larger artwork with many icons moves to 1/6 duty or more, as on S4101D (1/6 duty, 1/3 bias, 3.0 V), and then HTN or STN glass is used to keep the contrast. The theory, including the 1/(√N + 1) bias rule, is in segment LCD duty and bias.

The duty also has to match the driver. An MCU with a built-in LCD peripheral supports a fixed set of duties and a fixed number of COM and SEG pins, and a dedicated segment driver IC has its own limits. Confirm the driver before the pin map is drawn.

Assigning segments to COM and SEG lines

Once the duty is fixed, each SEG line can carry one segment per COM. The assignment is a layout decision and a firmware decision at the same time, so these are the rules we follow:

• Keep a digit on as few SEG lines as possible. At 1/4 duty, a seven-segment digit with its decimal point fits on exactly two SEG lines, as in the figure. Firmware then writes one digit as two 4-bit values.
• Put the same segment of every digit on the same COM. If “a” is on COM1 for digit 1, put it on COM1 for every digit. The font table in firmware stays one table.
• Arrange COM electrodes in bands. Commons that run as horizontal bands across the artwork keep COM traces short and leave clear channels for SEG traces.
• Watch very large segments. A large icon or a bar-graph background is a large capacitor. Give it its own SEG line, or split it, so the driver’s output current is not the limit and it switches as fast as small segments.
• Keep two or three spare SEG positions. An icon that marketing adds after the glass is tooled usually fits into a spare position. Without spares, it means new tooling.
• Match the pin order to the driver. The ITO routing on the glass can usually put pins in the same order as the MCU or driver pins, which saves PCB crossings. Send us the driver pinout with the sketch.

Routing ITO without ghost segments

The traces that bring each segment to its pin are transparent ITO on the glass, not copper on a PCB, and they behave like electrodes. Wherever a SEG trace on one glass passes over a COM electrode on the other glass, the overlap is a small LCD cell. When that COM is selected, the overlap sees a voltage and can show as a faint line or dot next to a real segment. This is the classic ghost segment, and it gets worse at higher duty, where the off-voltage is a larger part of the on-voltage.

The cure is in the routing:

• Route SEG traces only through areas where the opposite glass has no COM electrode, usually the gaps between segments. Route COM traces the same way past SEG electrodes.
• Where a crossing cannot be avoided, keep it as short as possible and place it outside the viewing area or under the bezel.
• Keep traces to large segments wide enough. ITO is resistive (LCD glass is commonly specified somewhere from about ten to a few hundred ohms per square), so a long, thin trace feeding a big segment charges it slowly and can show uneven contrast, most visibly in the cold.
• In reflective and transflective glass, wide ITO areas can be faintly visible at some angles because ITO has a different refractive index from the surrounding layers. Keep large unused ITO areas out of the viewing area.

A related effect, crosstalk, comes from the off-voltage every multiplexed segment sees and from fringe fields across very narrow gaps, rather than from routing. If a design will run at a high duty, ask for the gap and voltage margins to be checked at the lowest operating temperature, not only at room temperature.

Glass margins, the connection ledge and tolerances

The artwork does not go to the edge of the glass. The perimeter seal that holds the liquid crystal, the traces that run round it and the cutting tolerance all need space. Our catalogue drawings show what this looks like in practice:

Three things stand out. First, on the three parts with a rectangular viewing area, it sits 1.5 mm inside the front glass on every side, which is a sensible starting margin for a new design. Second, the rear glass is 2.0 to 4.7 mm taller than the front glass on the connection edge; that ledge carries the exposed ITO contacts the pins clip onto. Third, all outlines are ± 0.20 mm, each glass layer is 1.10 ± 0.10 mm and the LCD is 2.80 mm thick at most. Size the bezel window and the PCB cut-out for those tolerances, not for the nominal numbers.

Inside the artwork, the process limit for the gap between two segments is very small, but readable digits use much wider gaps than the process minimum. Copy the proportions of the digit style you want to match; the Digital-7 and seven-segment font guide explains how a font mock-up becomes glass artwork. The 7-segment LCD display guide covers digit types and pin counts.

Choosing the connection with the pin map

The pin count and the connection type decide each other:

• Metal pins (2.00 mm and 1.80 mm pitch on the references above) solder into the PCB and suit vibration and wave or hand soldering. The ledge has to be wide enough for the clip.
• Zebra connectors need flat ITO pads on the ledge and a clamp that controls compression. They need no soldering and suit long contact rows, as on S4056D with its 152.20 mm wide viewing area. See the LCD zebra connector guide.
• Heat seal or FPC carries finer pitches and lets the board sit away from the glass, as on the large S3966D with heat-seal connection.
• Chip-on-glass puts the driver on the ledge, so a large pin map collapses into a short FPC. This is covered in COG vs COB LCD modules.

The LCD connection guide compares the options side by side.

What the drawing package should contain

A first sketch can be a hand drawing. What we need to turn it into an approval drawing is:

1. The outline you can accept, the viewing area and the position of the connection edge, with the tolerances your enclosure can take.
2. The artwork as a vector file (DXF, AI or PDF), with each switchable element named and fixed legends marked as “printed”.
3. The driver or MCU part number and its COM and SEG pin count, or the pin budget you want to hit.
4. Drive conditions if they are already fixed: duty, bias, LCD voltage and frame frequency (64 Hz is typical on our references).
5. The optical choices: LC mode, positive or negative, transmissive, transflective or reflective polarizers, viewing direction and backlight colour. The monochrome LCD types guide and the viewing direction guide help with these.
6. Operating and storage temperature. Below about −20 °C the choices narrow; see wide temperature segment LCDs.

We return a drawing with the COM/SEG table and pin assignment for approval before any glass is made.

Mistakes we see on first sketches

• More switchable elements than the chosen driver can address, found only when the pin table is drawn.
• Icons drawn touching each other or the digits, leaving no channel for traces.
• Fixed text drawn as segments, using pins that a printed legend would save.
• No viewing direction given, so the glass is tuned for the wrong angle and looks weak in the product.
• A decimal point placed on its own SEG line, far from its digit, which makes firmware awkward.
• The outline drawn to nominal size with no tolerance, so the glass jams in the bezel.

Video: Segment LCD Design, From Sketch to COM/SEG Pin Map

This SuccessLCD explainer walks through the pin count, the duty, the COM/SEG assignment, ITO routing and glass margins of a custom segment LCD, with real SuccessLCD samples from static drive to 1/4 duty.

Segment LCD Design FAQs

Related engineering guides: segment LCD duty and bias, 7-segment LCD displays, LCD zebra connectors and COG vs COB LCD modules.