Custom Segment LCD (7, 14, and 16 segment displays)
Custom Segment Liquid Crystal Displays are seen in products that measure the PH level of swimming pools, monitors used to measure specific gases in a mine, or in thermometers used to see if a child is running a fever. They are one of the oldest display technologies, but still one of the most popular.
There may have been one on Noah’s ark to keep track of the number of animals or maybe the number of days it had been raining.
These displays are still one of the most popular technologies in use and the majority of them are custom.
Many people think the process of designing a custom segment liquid crystal display is complicated and too complex to be understood except for a few experienced people. But after designing custom LCDs for over 14 years, it can be said that just about anyone can select the best options for their product.
In other words you don’t have to be an engineer or have a PHD from MIT to design a custom LCD for their application.
So, instead of offering a list of technical terms and equations, these are the different options available.
What are the advantages of segment displays?
Although Segment displays are an older technology, it is still one of the most popular. After all, they cannot display all the colors of a TFT or OLED like what can be seen on a cell phone and tablet. Why?
Below are key reasons why people keep designing these LCD displays into new products.
Lowest unit cost
The unit cost of a segment display can range from less than .50/each to $15/each depending on quantity, size of glass and other variables.
Lowest tooling cost
The tooling cost for a custom display is the lowest of all the technologies and allows the customer to receive a LCD that is manufactured to the exact dimensions requested including custom icons and segments.
Focus Displays offers a one-time NRE (Non-recurring engineering) or tooling cost. This includes all design, support and samples. A PDF showing an overview of our tooling process can be found by clicking here: Custom LCD flowchart
Segment displays require less power than other display technology such as TFT, OLED, and BTN (Black Twisted Nematic). This makes these LCD displays ideal for applications that are battery powered or solar powered.
They require the lowest power to drive, an estimated 2uA per Centimeter squared. Glass only displays (no backlight and no controller) require an estimated 10% of the power that is required for a LED backlight. In other words, a static display without a backlight will draw around 1mA; the same display with a LED backlight will demand from 10mA up to 25mA.
Most displays can be driven at 3.3V or 5V since microprocessors can operate at both voltages. 3.3V is becoming more popular since two double ‘AA’ batteries can produce between 3.0V and 3.3V.
Segment LCD displays, also called static displays or glass-only displays, are constructed of two pieces of ITO (Indium tin oxide) glass with a twisted nematic fluid sandwiched in between. A static display is a segment display with one pin for every one segment.
Let’s start with “what is a segment”
A segment is any line, dot or symbol that can be turned on and off independently. The photo below is of a segment LCD that contains numbers, a small clock symbol, the word ‘Jul’, and the letters ‘PM’
An introduction to custom segment displays
What is a ‘seven’ (7) segment?
There are four numbers in the above LCD (0 8 4 7) all are seven segments. In other words the ‘0’ has seven segments, the ‘8’ has seven segments and so on.
Each number has seven independent segments. Each segment can be turned on and off independently to create other numbers and some letters such as E, F C and others. This is an example of a ‘seven’ segment. But there are some letters that a seven segment cannot display such as the letter ‘M’ or ‘V’. In this case a fourteen segment configuration can be used.
A fourteen segment is able to display any number and even more letters than the seven segment.
An icon is a small symbol or set of words that is only one segment. In other words, when the segment is ‘on’ the full word or symbol turns on. When it is “off”, the screen is blank.
In the photo above: the clock symbol is one segment, the word ‘JUL’ is one segment, the letters FOCUSLCDS.COM are one segment and the letters ‘PM’ are one segment .
This type of custom display can contain any icon required by the customer. Common icons include:
Plus and Minus signs (+ / – )
The advantage of icons is that they convey a message that can be understood in any language. An example of this is the battery symbol, this icon is understood anywhere in the world.
It is possible to burn a segment into the glass so that it is always “on”. In this case, the ‘FOCUSLCDS.COM’ has been burned into the glass and can always be seen by the customer even when the power is “off”.
Some customers will have their company name burned into the glass.
Hence the display is called a segment display because each segment can be turned “on” and “off” individually. You choose the number of seven or fourteen segments and which icons you want on your custom display.
How is a segment LCD built?
Segment displays earn the name ‘glass only display’ because the majority of them are glass with small metal leads attached to both sides of the display. However, it is possible to add a PCB (Printed Circuit Board) or a controller driver chip (IC).
The construction of the display is similar to that of a sandwich. You take two pieces of glass, glue one piece on top of the other, than inject a fluid between the two pieces of glass. In the drawing below you see a side view of a segment display.
The glass on top is smaller than the glass on the bottom. This is to allow room for the pins.
Segment display operating temperatures:
Segment LCDs, like all LCD display technologies, operate best between specific temperature ranges. You choose the temperature ranges that it will operate in. There are two standard configurations: normal temperature and wide temperature. The wider the temperature range, the more expensive the display.
The standard operating temperature range for a segment LCD is -20C to 50C.
It is possible to build the display with a different fluid that will allow it to operate from -30C to 60C (F).
With the addition of a heater, the display can operate down to -50C.
So what happens when the LCD becomes too hot or too cold?
When the display becomes too cold, the fluid between the two layers of glass starts to freeze; when the display does freeze, the segments that were “on” when it froze will stay on. The display will not change until the temperature increases.
When the display becomes too hot, a black spot will develop in the center of the glass. Basically the fluid is boiling. When the temperate comes down, the display will operate normally.
How sharp of an image will you need?
There are four types of Nematic fluids that can be placed between the layers of glass. Each one has advantages and disadvantages.
TN fluid – Twisted Nematic fluid is the lowest cost and has the narrowest viewing angle. It does have a faster response time in colder weather than STN and FSTN
STN fluid – Super Twisted Nematic fluid is more expensive than TN and offers a wider viewing angle than TN.
FSTN fluid – Film Super Twisted Nematic fluid is more expensive than STN and offers a sharper contrast than TN and STN.
VATN (BTN) – Vertically Aligned Twisted Nematic is only available in negative mode (light colored letters on a dark/black background). VATN displays produce very bright segments and can be easily read.
Thanks to color silk screen technology, you can now add color to your custom segmented display without increasing power consumption.