Display

A product can communicate in several ways with people. One of those is by using a display. This can show plain text, but graphic displays can also show pictures, graphs and icons. Dependent on the product’s requirements we choose an appropriate display. There is enough choice.

LED: (alpha)numerical displays

A number of Light Emitting Diodes (LEDs) are positioned in such a way that numbers can be shown. Seven LEDs can show the numbers from 0 through 9. Hence the name “7-segment displays”. By adding a number of LEDs the entire alphabet can be displayed.

Advantages:

• Good useable both in the dark (LEDs produce light) as in bright sunlight.
• Good readability.
• Affordable.
• Easy to integrate.
• Every number of characters per line and any number of lines is possible.
• Quite some choice in size.
• Colour can be red, yellow and green, and nowadays also in blue and white.
• Large temperature range.
• Mechanically robust

Disadvantages:

• Old fashioned image (the red displays exist quite a long time).
• Current consumption is relatively high.
• Hardly available as SMD component.

LED: graphic displays

These consist of a matrix of LEDs and allow to show graphic images. Combining a large group of these displays makes one large LED matrix that can display images.

LCDs

These displays consist of a mirror plate, two polarized glass sheets with a liquid crystal inbetween. Hence the name Liquid Crystal Display or LCD. By applying an electrical voltage on the crystal the orientation of the polarization changes. Combined with the polarized glass, light will be absorbed or reflected by the mirror plate. When light is reflected, the display colour is determined by the colour of the crystal. When the light is absorbed you’ll see that always as black.

As LCD’s work through reflection of light, they can’t be used in the dark just like that. Simply said, you can mount a light behind it and remove the mirror plate, which is called “backlight”. Sidelighting is also possible. There are some lighting solutions (LED, CFL or EL), each with it’s own advantages and disadvantages.

LCDs: alphanumerical displays

An alphanumerical display can show numbers, letters and punctuation marks. And tiny images as well because the characters are usually made up of a 5 x 7 dot matrix.

Available models (these can be both anvantages or disadvantages):

• A limited number of character sizes is available.
• The number of characters per line is 8, 16, 31, 64 or 128.
• The number of lines is 1, 2 or 4.
• Colour can be grey, green, yellow and blue.

Advantages:

• Low power (except for the backlight).
• Alphanumerical characters are standard.
• Low cost.
• Easy to integrate.

Disadvantages:

• Glass is vulnerable.
• Modest readability in sunlight.
• Backlight is necessary if used in the dark.

LCD: graphic displays

A graphic display can show pictures, graphs and icons. This opens more possibilities to design a user interface than any other display technique.

Available models (these can be both anvantages or disadvantages):

• A number of standard matrix sizes are available. Some of those are derived from VGA (640×480).
• With or without backlight.
• With or without touchscreen.
• Colour or monochrome.

Advantages

• Many possibilities to show pictures and to design a language independent user interface.
• Looks good and modern.
• Touchscreen is often a possibility, so sometimes no other controls are necessary.

Disadvantages

• A colour LCD is not really beautiful.
• Glass is vulnerable.
• Badly readable in sunlight.
• A backlight is necessary when used in the dark.
• Relatively expensive.
• Often a complex control unit is required, one that has lots of processing power and more memory.
• Temperature range is usually limited to 0 – 50 °C

TFT, OLED, VFD and other “active” displays

An active display is a display that produces light by itself, just like a LED. In a TFT display this is done by a transistor matrix (Thin Film Transistor = TFT). In an OLED display this is done through Organical LEDs, where an organical substance is sandwiched between two glass sheets. When a voltage is applied the material lights up in a pre-defined colour.

TFT displays produce a beautiful image, are modest to read in sunlight, have a long lifetime and are relatively expensive.

OLED displays produce a beautiful image, can be quite easily produced and are relatively cheap. Ideal for PDA’s, photo cameras and mobile phones. They only have one disadvantage: a short lifetime. The blue colour will stop after 1.000 hours, the red colour after 10.000 hours and after 30.000 hours green is gone too. But basically the display is used up after 1.000 hours and that’s very short.

VFD displays are gas discharge displays. These are the green/blue displays that are used a lot in DVD players and VCR’s. They are available in one colour only, are quite large, use quite some energy and are vulnerable. But they are very good useable in the dark or in sunlight and can operate within a large temperature range.

What to choose ?

That depends entirely on the product requirements. And that’s why we like to think together with you. We know the advantages and disadvantages and we like to help you making the right choice. Please feel free to contact us if you like to discuss your requirements. We really like to help you out.