HP Forum Archive 13

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Green LED's? Message #1 Posted by Katie on 21 Nov 2003, 5:08 p.m. Although this is somewhat off topic, I know that this is the best place to pose my question -- all the experts are here! Quite often on ebay and elsewhere you see people that advertise their old calculator as having a "Green LED" display. Invariably (always, actually) these are not green LED display calculators, but some form of vacuum florescent display -- the seller has no idea what a Green LED is, no doubt. Anyway, my question is this: Did any manufacturer ever make a calculator with a real green LED display (or yellow for that matter)? If I remember correctly, 7-segment LED displays were available in green and yellow before 1980 when most calculator manufacturers switched to LCD displays. Thanks, -Katie

Re: Green LED's? Message #2 Posted by Michael Meyer on 21 Nov 2003, 6:54 p.m., in response to message #1 by Katie Great question, Katie!!!! When I stop and think about it, I've had the same experience.... I can't think of any true LED displays that weren't red.... I know my Sinclair has a purple lens, but I think it's still a RRREEEEDDDD LEEEEDDDDD <grin>). I'll look through my collection and see what I find. I still owe you a favor, BTW... (though still haven't gotten my circuit to work....) Regards

Re: Green LED's? Message #3 Posted by Trent Moseley on 21 Nov 2003, 11:20 p.m., in response to message #1 by Katie Katie, I have a 1972 Heathkit with yellow (amber) LEDs. tm

Re: Green LED's? Message #4 Posted by Katie on 22 Nov 2003, 12:22 a.m., in response to message #3 by Trent Moseley That's pretty amazing and must have been quite expensive, are you sure it's really an LED display? According to this article http://www.spectrum.ieee.org/WEBONLY/publicfeature/jun03/med.html the yellow LED was only invented in 1970. Although the red LED was invented in 1962 it took 7 or 8 years before it got into commercial products.

Re: Green LED's? Message #5 Posted by Trent Moseley on 22 Nov 2003, 2:36 p.m., in response to message #4 by Katie Re the Heathkit. I haven't had it out of the closet for years. Just plugged in in. My wife says they are orange. But they aren't red. tm

Re: Green LED's? Message #6 Posted by Thomas Radtke on 22 Nov 2003, 2:49 p.m., in response to message #4 by Katie The very first pocket calculator with LED was the '71 Bowmar 901B:). Thomas

Re: Green LED's? Message #7 Posted by Richard Garner on 22 Nov 2003, 12:23 a.m., in response to message #1 by Katie I had an old 4 banger desk unit with sq root, % and 1 memory register, can't remember the name. It had white or very light yellow LED's that were viewed through a blue display cover.

Re: Green LED's? Message #8 Posted by Andrés C. Rodríguez (Argentina) on 22 Nov 2003, 10:00 a.m., in response to message #1 by Katie Katie: I think I haven´t seen any "real green LED" calculators, I could remember that green LEDs were anything but common before 1980 (of course in my country, but also in most USA and european electronics magazines I was subscribed to). Even the "activity" or "power on" LED in commercial computers (i.e.: Data General, IBM, Compaq, Bull), disk drives (Shugart, Seagate, Fujitsu), early PCs, floppy drives were usually red until 1988 and even later. I assume that the higher cost and, for portable equipment, power budget could have been barriers for massive adoption of non-red LED. I vaguely remember something about GaAsP vs. GaP processes that may also have something to do with cost and availabity. As the light wavelength relates with the voltage drop in LEDs by means of the equation E=hf, where E is the energy in electron volt units, h is Planck constant andf is the frequency, it follows that green (and yellow) LEDs have a higher operating voltage than red ones. While the greater eye sensibility for green may reduce operating currents, I think that the voltage issue may have been a factor preventing a faster adoption for portable electronics. Edited: 22 Nov 2003, 4:12 p.m. after one or more responses were posted

Re: Green LED's? Message #9 Posted by Katie on 22 Nov 2003, 1:29 p.m., in response to message #8 by Andrés C. Rodríguez (Argentina) I do have one calculator that uses 3 yellow LED's -- 3mm size single devices, it's the Kosmos I. I think that this calculator dates to around 1978. But what I'm really looking for is a calculator that used a yellow or green 7-segment display. Edited: 22 Nov 2003, 1:30 p.m.

Re: Green LED's? Message #10 Posted by Andrés C. Rodríguez (Argentina) on 22 Nov 2003, 4:23 p.m., in response to message #9 by Katie Yes, things were the way you stated. Individual LED lamps and single digit seven-segment displays were usually red, and the same happened for the multiplexed, n-digit "display sticks" used in portable electronic devices. By the time non-red LED lamps and non-multiplexed displays started to be more common (~1980?), most calculators were shifting to LCD's, featuring also more meaningful status indicators and even alphanumeric output. I also have (many, many times) seen and heard about "green LED" displays which in fact were fluorescent types. Also (at least here) many people confuses "quartz crystal" (for time reference) with "liquid crystal", and journalists or TV reporters write and talk all the time about "liquid quartz" devices (sic).

Re: Green LED's? Message #11 Posted by David Smith on 22 Nov 2003, 12:57 p.m., in response to message #1 by Katie TI made some green and yellow LED calculators. They were for market test purposes only and never sold to the public or let out of TI control. A friend of mine snagged several of them from a trash can. There was even an LCD SR-51.

Re: Green LED's? Message #12 Posted by David Smith on 22 Nov 2003, 12:59 p.m., in response to message #11 by David Smith Forgot to mention the green LED Compuchron watches. Even rarer were the orange and yellow ones. The yellow LEDs in particular were not very bright or even in their illumination. Compuchron pulled them off the market rather quickly.

TI green/yellow LED calculator Message #13 Posted by Katie on 22 Nov 2003, 1:33 p.m., in response to message #11 by David Smith That's a great collectible! Does your friend want to sell one to me?

Re: TI green/yellow LED calculator Message #14 Posted by David Smith on 23 Nov 2003, 3:04 p.m., in response to message #13 by Katie Nope, I've tried everything short of homicide to pry them loose from his tight fisted paws...

Re: TI green/yellow LED calculator Message #15 Posted by Katie on 23 Nov 2003, 7:22 p.m., in response to message #14 by David Smith I applaud your restraint, homicide might be talking this calculator collecting hobby just a bit too far :)

Re: Green LED's? Message #16 Posted by Joerg Woerner on 24 Nov 2003, 2:41 a.m., in response to message #11 by David Smith Hi David, I'm the Curator of the Datamath Calculator Museum featuring the TI products. Could you forward me the address of your lucky friend ? Regards, Joerg

Re: Green LED's? Message #17 Posted by David Smith on 25 Nov 2003, 12:54 p.m., in response to message #16 by Joerg Woerner I have not seen him in many years. He moved out to the west coast after leaving TI... I don't know where. He stored a lot of his electronics with me before he left so I got to play with them. Then he came back for his goodies (bummer). If he turns up, I'll send him your way.

Re: Green LED's? Message #18 Posted by Tom (UK) on 24 Nov 2003, 12:23 p.m., in response to message #1 by Katie Katie, I think it's just physics. Red LEDs don't need as much forward bias (as someone else said) and I think they are also much better at turning electrons into photons, the GaAs LEDs are even better and HP were a leading supplier. As the LEDs were a big drain on the battery then red LEDs were the the only sensible choice. There is also the fact that Yellow and Green LEDs came on the market at prices that could be used just when makers were turning to LCDs for calculators. I also see many ads for 'green LED' that turn out to be the short lived VFDs period of calcs. But more recent consumer products (pocket computers and mobile phones) usually have Greenish or Yellowish backlighting, I assume these are LEDs, I suppose Red LEDs would not provide enough contrast with an LCD screen. HTH Tom.

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