Take a look at alphanumeric displays, they're changingSteve BushTwo line alphanumeric displays are an enduring classic among components. Introduced 20 or so years ago, construction techniques and technologies have changed, but the basic product has endured.
This has much to do with utility - two rows of 16 or 20 characters allows a lot of information to be displayed in a legible - if uninspiring - format.
Longevity has also been assured by the 5V 14-wire parallel interface - set in stone by the Hitachi HD44780 interface chip and actually out-living the original - as only non-Hitachi equivalent ICs are now available to display makers.
"Everyone knows and loves the interface," said Jim Hemsley of Trident Displays, which distributes alphanumeric displays made by Varitronix. "We do some 3V versions, but lots of people prefer 5V because they know where they are with such an industrial standard. They move their design straight into new products."
Things have moved forward in those 20 years. Smaller and larger displays can be bought, chips are wire-bonded straight into the modules and STN (super-twist) LCDs have to some extent replaced the original TN (twisted nematic) LCDs. And more recently film-enhanced STN (FSTN) has become available. "TN has poor viewing angle, but good contrast from the right direction and is the cheapest," explained Hemsley. "STN had a wider viewing angle but is restricted to black characters on a green background. Adding a film allows a grey background with a viewing angle similar to STM."
All three are available in either non-backlit reflective or back-lit transflective (with two additional backlight pins) forms. "From our point of view, white and blue LED backlights have been the most significant recent development," said Hemsley.
Inverse LCDs, with light pixels on a dark background, can also be found. Other technologies vie to provide the characters within 2x16 displays. The most significant is VFD (vacuum florescent display) which is inherently emissive, and inherently more expensive than LCD. "Compared with VFDs, virtually all other technologies suffer in hot, humid or salty conditions," said Andrew Stubbings of Itron(UK), pointing out VFDs are frequently specified to operate from -40 to +85 deg C.
Itron, part of Noritake Itron, manufactures displays in the UK. Its UK-made displays have a microcontroller inside with mimics the Hitachi interface, and also allows additional flexibility. "We can offer custom fonts, and our 7000 series can be switched into 16x96 dot graphics mode," said Stubbings. "In our niche market, we have to be innovative."
VFDs are also bright, up to 1,000cd/sq. m, and the broad spectrum of wavelengths emitted - which appears blue-green - can be filtered to get various colours. "You can get anywhere from white to blue," said Thomas Tuxen of Review Displays (RDS) - a distributor which sells VFDs from Futaba alongside LCDs from Optrex, Palm Technology and Emerging Display Technology (EDT). He sees audio-visual equipment suppliers using VFDs. "In AV-equipment, viewing angle is more important than price," he said - and agrees with Itron's Stubbings that VFDs beat LCDs in tough environment.
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