who still use led displays? Is LCD domination complete?

Edited: 18 Sept 2009, 9:56 p.m.

If any calculators with LED displays were manufactured and sold in the last 20 years, it's news to me.

I guess LED backlights don't count :-)

Anyway, my first though was the various Soviet calculators might have LED models less than 20 years old -- they certainly have VFD models younger than that. A bit of searching and I found the
Elektronika MK-37 which has a LED display and was manufactured less than 20 years ago.

- Pauli

Of course there are countless numbers of non-battery powered desktop calculators that use LED displays, such as the following:

<see here>

Were you perhaps thinking of small battery powered calculators, such as the HP classics, Woodstock and Spices (Spicem)?

Edited: 19 Sept 2009, 2:23 a.m.

I think that most of these are fluorescent displays -- even though this manufacturer says it's LED. I did come across this Casio calculator that has a 2-color display. I have no idea what technology that is, I've never seen a bi-color 7-segment display.

The name digitron refers to VFD (vacuum fluorescence display) tubes, but the technology does not allow for a segment to have two different colours - only for different segments to have different colours. That Casio is an intriguing machine...

marais

LEDs are being used to make some spectacular computer displays nowadays. A modern LED based calculator might not resemble the old machines at all. Such a calculator certainly wouldn't consume power at the rates the old machines do either.

Regards,
Howard

A careful look at the two different colour images shown, it seems that the same digits do not quite line up. So it could be VFD, just different colour segments of each digit next to each other?.

...well, that's not exactly a LED display, just a LED backlit LCD screen with a misleading name. I agree though that the result is stunning.

marais

Yes.

It's called a PDA.

A lot of solar-powered LCD calculators use an internal LED in the voltage regulation circuitry. But...that's not a display.

Quote:

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The name digitron refers to VFD (vacuum fluorescence display) tubes, but the technology does not allow for a segment to have two different colours - only for different segments to have different colours. That Casio is an intriguing machine...

marais

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Looking at the pictures of the display, one notices that the shape of the digits is not exactly the same between the two colors. Notice in particular the hole in the upper right part of several digits: 2, 3, 7, 8, 9, 0. This leads me to believe that each segment is actually made from two VFD tubes put side by side.

Does OLED count? That could become viable in the not too distant future.

Quote:

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Does OLED count? That could become viable in the not too distant future.

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OLED is already viable, has been for quite some time.

Likely rules out a nice looking 7 segment display version though, unless you pulled a trick or two.

Dave.

From what I've read recently OLED's have a theoretical efficiency only slightly higher than conventional LED's. This means that they still suck up too much power to be viable for a hand held calculators. Which is why they were abandoned in 1980 (roughly).

I think that Casio got the "right" calculator display on their fx-9860G series with the switchable backlight. I'm not sure what they use but it looks like it's electroluminescent. It's plenty bright and uses just 30mW of power. On 2 AAA cells it provides back lighting for 3 or 4 days of continuous use.

I know they are in production but pricing is still on the high side, that was my real point regarding viability.

How about a return to the tritium phosphor LCDs that TI and a few other manufacturers used on some LCD watches in 1978? They were wonderful, putting out enough light to be able to illuminate not only the watch display, but also anything held in front of the display as well. In blackened control room conditions on the submarine I was on, those wearing such watches could easily be noticed across the compartment. The display used no battery power, and required no button pushes to read in the darkness. These were the best watch displays ever made, IMHO.

For some reason, by 1979 TI had discontinued all such watches and gone to a power-consuming micro light bulb which required the push of a button to activate.

I've always wondered if it wasn't anti-atomic idiocy that made it politically incorrect for TI to use such displays, especially after Three Mile Island.

One (minor?) problem: Tritium has a half life of just over 12 years.

Depends on your philosophy about how long your calculator should work. It seems that most of us here hope/expect to use our HPs nearly forever. A tritium-powered HP35 from the early 70s would now be only about 1/8 as bright as originally (assuming the brightness of the display is proportional to the tritium decay activity).

I've never seen one of those LCD watches, but still have an alarm clock with a radium painted dial. They still make tritium clocks and watches. But these only have a very small amount of tritium on the face. I realize that the beta particles emitted by tritium are very low energy and won't penetrate a good glass watch face. However, I wonder if there are problems with the radiation heading into modern clock/calculator chips with their sub 100nm transistors and thin epoxy blob coatings. A large area that would be needed for an LCD backlight might generate enough radiation to randomly mess with the microelectronics.

Edited: 23 Sept 2009, 12:05 p.m.

Love the product names on the watch and clock: H3 - the element designator (H) and atomic weight (3) of tritium.

It could also be a reference to Harrison's H3.