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Old 22nd Sep 2019, 1:07 pm   #21
Refugee
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Default Re: Your first experience with LEDs?

This cleaver dove found a novel use for an LED street lamp.
It installed its nest on the heat sink fins so that the eggs got night time heat to assist incubation.
Success is indicated by the presence of LED incubated chicks.
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Old 22nd Sep 2019, 1:27 pm   #22
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Default Re: Your first experience with LEDs?

The phrase 'Bird brain' isn't quite the insult it used to be!

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Old 22nd Sep 2019, 1:29 pm   #23
60 oldjohn
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Default Re: Your first experience with LEDs?

Quote:
Originally Posted by Argus25 View Post
Quote:
Originally Posted by woodchips View Post
Do LEDs fade?
Yes they do. Some of the early Red ones from the 1970's era are still pretty good, others have faded away to nearly zero light output.
I may have been lucky.

My first LEDs were the MAN3640 seven segment display. I used them in a clock in 1975. In 2007 I started a thread "What is your oldest homebrew / kit still in use today" Well another 12 years later and here it is today, still in use. It was made from an article Practical Wireless September 1975. And here it is today with hardly a day off in the last 44 years. With no sign of fading,,, yet. I had trouble taking the photo, had to have bright lights on. It is brighter than it looks in photo.

John.
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Old 22nd Sep 2019, 1:35 pm   #24
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Default Re: Your first experience with LEDs?

I remember "Lumenition" - one version was just the LED/photocell, chopper-disc and a current-amplifier - there was also another version that used the LED/photocell to trigger a capacitive-discharge system with an inverter to chage the capacitor to 400V or so, and a Thyristor to dump the charge into the coil, just like a photo-flash.

Blue LEDs - and then white - were indeed a major revelation in terms of photons-produced-per-milliamp-of-current-drawn! My first TIL209 needed 20mA to produce a bit of red; now a Milliamp will produce impressive whiteness.

When I got the TIL209 I built a "LED Flasher" circuit - a classic multivibrator with a pair of BFY51 transistors, one of which had the LED and its dropper-resistor as the collector load. This fascinated people at school; they were equally fascinated the following week when I 'miniaturised' the circuit by using a LM3909 IC as the flasher. This was actually small enough to be built into the body of a flashlight, with the LED poking through a little hole drilled in the reflector. Its average current draw was tiny (a few Microamps) so could be wired permanently across the battery. A good way to help you find your flashlight in the dark - I think I charged kids £1.50 a time to fit these! Cunning thing about the LM3909 was that it included a voltage-doubler circuit so it would power the LED even when the battery was getting _really_ weak.

Then came LEDs with built-in flashing circuits - and the "three-legged" bi-colour ones, which were great as go/no-go indicators - I remember there being a 'military' antenna-tuner (I think it was by Harris) that used a pair of these fitted side by side above the knob for rotating the roller-coaster coil: when it was mismatched one LED was red the other green; you turned the knob in the direction of the one that was green until they both went green, and the job was done. Cheaper than a meter, and much more squaddie-proof.
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Old 22nd Sep 2019, 2:36 pm   #25
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Default Re: Your first experience with LEDs?

I recall being given a very early red LED by a neighbour who worked in the electronics trade.
Within a year these were sold at high prices, and within a few years became cheap.
I purchased an early white LED from RS many years later.

As regards the variable quality of cheap new blue or white LEDs, It can be worth selecting these components for quality.
Practical LEDs seem to consist of a "perfect" LED shunted by a high resistance. In time the value of this resistance seems to fall until it draws significant current.

To select the best examples, reverse bias each LED at a very low voltage such as 4.5 volts from 3 dry cells. Measure the current with a suitable meter, the lower the better.
More than 500 microamps Is faulty IMHO.
Less than 1 microamp is good.
Intermediate currents are a value judgement.

Alternatively, forward drive the LED from say a 9 volt battery and a very high series resistance that limits the current to say 10 microamps.
The better examples will light, very dimly, at this minute current, the lower quality LEDs wont light even dimly because all of the small drive current is being shunted.
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Old 22nd Sep 2019, 3:51 pm   #26
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Default Re: Your first experience with LEDs?

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Originally Posted by cheerfulcharlie View Post
Then I came across this kit called Lumignition which fitted in the distributor, it consisted of an LED, a photocell and a plastic paddle you fitted on the rotor to sequentially break the beam and outside was a small amplifier box to deal with switching the coil.
It was such a good idea at the time that worked reliably, you wondered why car manufacturers had up to then never bothered evolving the ignition system and electronic ignition was not going to be fitted en mass for probably another decade.
Technology can work both ways!

I had a bike which I changed the points on to one of these. The first one failed within a week or so of fitting. The supplied replacement worked for a while, then developed a fault resulting in total ignition cutout, waiting ten minutes or, then restarting without problem. I went back to standard points as they were easier to fix by the roadside.
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Old 22nd Sep 2019, 3:51 pm   #27
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Default Re: Your first experience with LEDs?

AFAIR the first red LEDs we got at Plessey in the early 1970's cost around £2 each, but they soon got cheaper. Somewhere I have a set of the TI LED display ICs that incorporate logic that I got to use in a project that never got off the ground.
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Old 22nd Sep 2019, 5:47 pm   #28
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Default Re: Your first experience with LEDs?

I'm sure my first peek at an LED was on one of those 1970's taiwanese 'world band' radios that used an led on a long flex as the tuning indicator. I soon robbed that and played with it till I got a bigger battery and blew it.
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Old 22nd Sep 2019, 11:22 pm   #29
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Default Re: Your first experience with LEDs?

I bought a big bag of yellow 5mm LEDs either from a radio rally or from Bi-Pak in the early 80's. The poly bag was grubby and cloudy and had obviously been in storage for a long time. The legs of the LEDs were almost black with tarnish. On test, the LEDs were pretty dim no matter how much current I shoved through them. They were just about bright enough as panel indicators in subdued light, certainly nowhere near good enough for illuminating anything. I think I've still got some in the drawer, but only because I hoard stuff.
At the other end of the spectrum (!), I've got a few Luxeon 2-watt leds that I used for light-beam comms. When I first got them I tested one on the bench at just 30mA and was astonished at the eyeball-searing brightness! Firing one through a lens system to a photodiode (also in a lens tube) would carry baseband AM audio over several miles.
I believe ranges of over 70 miles have now been achieved. What an advance over our schoolboy experiments with a bike lamp and an ORP12 LDR!
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Old 22nd Sep 2019, 11:46 pm   #30
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Default Re: Your first experience with LEDs?

I have to admit that I have no particular recollection of my first LED experience. Perhaps it coincided with another first experience, if you catch my drift...

What I can remember is staring at the first liquid-crystal wristwatch I ever saw in a jewellers shop window, thinking how beautifully elegant it was, and what a game changer it would be.
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Old 23rd Sep 2019, 9:01 am   #31
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Default Re: Your first experience with LEDs?

I bought a Red one when they were quite expensive (£1?) from a shop in the Edgware Roard.

Tried it out on a park bench using a PP3 - without a limiting resistor. I hadn't read about those yet at the age of 11 or so.

When I got home I tried the same arrangement with a PP9. Something whizzed past my right ear and there was a funny smell in the room for hours. No more LED.

Then I found about the subject of limiting resistors...later on even internal resistance of batteries!
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Old 23rd Sep 2019, 9:25 am   #32
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Default Re: Your first experience with LEDs?

In 1978 I made a set of LED Christmas Tree lights. At that time I was doing research at Southampton University, and you could buy red and green LED's from the electronics department stores. Built a little power supply in an Eddystone box. They were dim and expensive by today's standards, but we used them every year until about ten years ago when we bought a couple of new sets - much brighter, and of course with blue too, which was impossible back in '78!

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Old 23rd Sep 2019, 9:31 am   #33
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Default Re: Your first experience with LEDs?

I'd read about them in a kids book from the library when I was at primary school in the early 1980s, but the only ones I'd seen were on my aunt's little Hitachi B&W portable telly, and my mum's Philips N2213 cassette recorder. I also distinctly remember my uncle being a smart-a*** in a family Christmas game of I-Spy in about 1980 and choosing "LED", and unsurprisingly, nobody getting it (although to be fair, it was glowing merrily in the corner)!

I then came across a pile of junk dumped on Wandsworth Common which looked like someone's attempt to build a toy robot. All trashed and rain-soaked, but I spotted some LEDs complete with nice long legs, so grabbed them, much to mum's embarrassment. I knew about series Rs but I could not get them to light up. But eventually, I threw caution to the wind and slapped one of them directly across a "dead" 4.5 battery which my dad had just removed from his bike lights. It glowed, and continued to do so for literally months on end. Presumably, the forward voltage and internal R of the battery were roughly right.

Nick.
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Old 23rd Sep 2019, 10:09 am   #34
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Default Re: Your first experience with LEDs?

My first encounter with LED's was back in the mid 1970's with a CBM calculator and a watch, both used red LED segment displays. Then through the 1980's LED's started to be used as stereo beacons, tuning and power indicators and level indicators using red, yellow and green LED's.
During the 1990'D I built a few of those Vellman Christmas LED kits, bought from Maplin, again made up of red, yellow and green LED's. These are still working today.
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Old 23rd Sep 2019, 5:21 pm   #35
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Default Re: Your first experience with LEDs?

Quote:
Originally Posted by Craig Sawyers View Post
In 1978 I made a set of LED Christmas Tree lights. At that time I was doing research at Southampton University, and you could buy red and green LED's from the electronics department stores. Built a little power supply in an Eddystone box. They were dim and expensive by today's standards, but we used them every year until about ten years ago when we bought a couple of new sets - much brighter, and of course with blue too, which was impossible back in '78!

Craig
I've made several odd LED Newtonsday [1] decorations involving vintage computers. One set consists of a length of tinsel with 16 LEDs fitted into it, red, orange, yellow, green repeated 4 times. The PSU contained 16 TTL-input drivers. I ran this thing off a parallel output port on a PDP11 (DR11-K) or PERQ (PERQlink)

I also made a couple of small 16-LED decorations, one a star, the other a tree These were controlled by HP calculators, either with an HPIL interface and HP82166 GPIO converter or an HP48 + a homebrew I2C interface + an SAA1060 IC.

[1] Sir Isaac Newton was born 25th December 1642 according to the calendar in use in England at the time. As an agnostic physicist I celebrate his birthday.
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Old 23rd Sep 2019, 7:06 pm   #36
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Default Re: Your first experience with LEDs?

Actually, Lumenition. It’s an infra-red chopper system, used it on my rally Mini in the 1970s and on my Triumph Stag today.
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Old 23rd Sep 2019, 7:38 pm   #37
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Default Re: Your first experience with LEDs?

https://vintage-radio.net/forum/show...2&postcount=20

I feel a thread merger coming on ...

Best wishes
Guy
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Old 23rd Sep 2019, 8:04 pm   #38
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Default Re: Your first experience with LEDs?

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Do LEDs fade?
Without a doubt some loose their output over time but the spread of performance in this respect seems quiet large so I'm not sure what's inherent in the technology and what's down to the manufacturing
We have also seen opto isolators suffer from degradation that was also put down to the internal emission dropping off.
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Old 23rd Sep 2019, 8:19 pm   #39
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Default Re: Your first experience with LEDs?

In 2001 or thereabouts I dusted off a microprocessor system - a 'A Maplin Z80 system' which I had put away working probably 6-7 years before. When powered up, the 7-segment address / display digits were so dim that I went looking for a fault on the display controller, found none and eventually replaced one display which came up bold and bright, even as the others in the (multiplexed) display remained wan and dim. I replaced the rest and they are still, about 18 years on, as bright as the day I fitted them.

I have no idea what happened to the original displays, since the system had been played with for about 1-2 years and then put away, so they had to have died from age alone or even from lack of use, rather than by exceeding their 'emission hours life'.

Like others above I still occasionally repair PCBs which our company made in the early 90s, on which the LEDs are constantly lit when the PCB is powered, and they can be very dim indeed.
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Old 23rd Sep 2019, 10:28 pm   #40
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Default Re: Your first experience with LEDs?

My first LED was a Texas TIL209 (Red, 1/8"). Not massively bright, even at 20mA. But price was about 23p in 1976 or early 1977.

I got fond of LED's despite them being s*m*c*nd*ct*rs (I like things that light up) so have tended to use them ever since.

I remember seeing in Electrovalue's catalogue, around 1992, their first blue LED. Was by Siemens. Price £27. They saw fit to put 'Really!' after the price (no, I didn't buy one) yet last week I threw out a 50p cigarette lighter which also had a couple of batteries and a blue LED in for a mini torch!
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