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Old 21st Sep 2019, 7:47 pm   #1
G6Tanuki
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Default Your first experience with LEDs?

I've always been fascinated by LEDs.

The first one I got to play with was a red TI "TIL209" bought via a friend who had a RS account. It was horribly-expensive [a day's wages before-tax&national-insurance!] so I was _very_ diligent about getting the polarity right and fitting a higher-than-usual series resistor [820 Ohms] before turning out the lights and flicking the switch to apply 9V from a Pp3.

It really was an "and then there was light!" moment.

Shortly afterwards, I acquired - again at some cost - one of the first 7-segment LEDs made by Monsanto, the MAN3A

http://www.decadecounter.com/vta/art...w.php?item=364

nicknamed "The Claw" because of its packaging. I hooked this up to a suitable TTL chipset for counter/decoder/driver and - loand behold - I could get it to cycle through 0-9 and ABCDEF by pressing a button to increment the counter!

At that point I was convinced that this really was the way ahead - a year later I'd designed my first 'commercial' piece of equipment that used an ultrasonic transducer and four 7-seg LEDs - it was used to assess the thickness of the back-fat on pigs in a slaughterhouse, and sold a few hundred - at over 1000 each!

What are your LED memories??
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Old 21st Sep 2019, 10:50 pm   #2
Richard_FM
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Default Re: Your first experience with LEDs?

I remember there was an early electronic game called Flashpoint which was a hand me down to me & my brother. The design of it was 1960s-70s.

It was a matrix of holes & a small jack plug on a cable, along with 3 LEDs indicating an arrow.

I can't remember the exact rules of the game but the jack was inserted into a hole an LED would light up to indicate in which direction the jack should be moved.

Eventually the jack cable broke & not having a soldering iron to fix it meant it was binned.
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Old 21st Sep 2019, 11:44 pm   #3
Ted Kendall
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Default Re: Your first experience with LEDs?

I first came across LEDs in the Henelec kit of the Nelson-Jones tuner, then shortly afterwards in the Sinclair Scientific calculator, two of which I built from kits one Christmas afternoon. Around this time, too, I remember them used in the on-board diagnostics of the Cambridge Classic amplifier, which appeared as a space-age looking protoype at Sonex one year. I still remember the rep expatiating on its many advanced features. It never appeared on the market, however, because the company collapsed shortly afterwards.
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Old 22nd Sep 2019, 2:15 am   #4
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Default Re: Your first experience with LEDs?

I vaguely remember buying a "bargain" pack of red LEDs in the mid-70s that weren't very good at all, probably from Tandy.
Then mail-ordering a kit for an LED alarm clock kit in the late 70s, but they had run out and sent me a ready-built Hanimex one instead, which worked for decades.
Some of the LEDs in the earlier (1978) equipment I repair at Work are quite dim now and require replacement, but only one or two have ever actually completely died.
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Old 22nd Sep 2019, 2:48 am   #5
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Default Re: Your first experience with LEDs?

I was building myself a little class A amplifier to drive a pair of Koss headphones that had been a birthday present in '73 and I picked up a few surplus LEDs at M&B in Leeds. One went in as power indicator on the front panel. At 20mA, the brightness was just right to tell the thing was on.

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Old 22nd Sep 2019, 3:19 am   #6
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Default Re: Your first experience with LEDs?

I can remember buying an LED to use on a MC1310 stereo decoder.
It saved having to use a transistor to drive a bulb and all the mains ripple that I would have endured.
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Old 22nd Sep 2019, 6:55 am   #7
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Default Re: Your first experience with LEDs?

I remember my late father coming home with an RS green LED in the early 1970s. He showed me how to calculate the series resistor (I think we used 470 ohms for a 9V battery which would give around 20mA) and I connected it up with such a resistor on a 'chocolate block'. That was probably the first time I saw an LED.

I remember rather more clearly when Maplin got their first blue LED in stock around 1990. I bougth the one they had in the Bristol shop (I was studying at Bristol University at the time), went back to the lab, stuck it in a breadboard with a suitable resistor and powered it from a bench supply. Word travelled fast, half the people in the building came in to see it.
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Old 22nd Sep 2019, 7:48 am   #8
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Default Re: Your first experience with LEDs?

Quote:
Originally Posted by Refugee View Post
I can remember buying an LED to use on a MC1310 stereo decoder.
It saved having to use a transistor to drive a bulb and all the mains ripple that I would have endured.
My first experience of LEDs was also on an MC1310 decoder around December 1972. I managed to blow it up when a croc clip fell into the tuner shorting one pin to ground putting 12V across the LED. I replaced it with a green LED which had recently become available and added resistor in both leads so I could short either lead to 12V or ground without causing any damage. I recall they cost about 35p.

At university we had a sample red LED which only just looked like a diode and was very dim. I recall we had about 200mA through it to get a dim red light from it just before it expired.

In 1974 had some sample HP LEDs, red, yellow and green but the green LED looked more yellow at low currents.

At work in the mid 90s we had a blue LED which wasn't very bright unlike todays offerings.

Keith
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Old 22nd Sep 2019, 7:54 am   #9
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Default Re: Your first experience with LEDs?

The first time I saw an LED was when I was working in the Philips workshop in Waddon (Philips Service). They used one as a sensor in a cassette player. It was a red LED and part of the end-of-tape motor stop circuit. It was mounted below a rotating vane which interrupted the light to a photocell causing pulses as the vane rotated. It was the first thing to check if the auto-stop didn't work......

It wasn't long before they appeared as indicator lights and backlights but of course they were early generations and not very bright. We never thought they would be developed as they are now for general lighting.

My first encounter with a blue LED was as a main beam indicator in one of the Philips Citroen fleet cars in the 1990's.

To me it seems that once blue LED's had been perfected, they seemed to appear everywhere!
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Old 22nd Sep 2019, 8:13 am   #10
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Default Re: Your first experience with LEDs?

I got hooked on the Texas instruments TIL311. These are a dot LED hex display, with the decoder chip inside the display package. You just drive them with 4 bit data.

I loved them so much I decided to make aclock, after I discovered an unusual variant of them, a cmos version made by Innocor in Canada. Here is the clock, I made it count up or down and both 12 & 24hr, I designed all of the circuitry myself. On count down it can stop at zero triggering some event like a laboratory experiment.

http://worldphaco.com/uploads/THE_CMOS_CLOCK.pdf
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Old 22nd Sep 2019, 8:59 am   #11
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Default Re: Your first experience with LEDs?

My very first would be in a calculator my dad bought. Commodore. Only had very basic functions though. Then my brother got an LED watch. You had to press the button to see the time.

First experience using them was for a project for a simple switch panel. The parts would have come from RS.

I do remember realising how expensive Tandy were to buy them. 1.40 for a standard red LED, where you could mail order ten for the same price from Maplin (before they went all Tandy on us).

It's amazing how the technology has changed. First the huge increases in light output, and more recently the massive reduction in If. I'd got so used to the value of resistors to give If=20mA at 12v and 5v that I never even calculated it. So when I was reviewing a design I immediately thought the designer had made a mistake with the resistor, given If would have bee just a couple of mA. See, still learning something new every day.
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Old 22nd Sep 2019, 10:18 am   #12
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Default Re: Your first experience with LEDs?

Do LEDs fade?

After graduating one of the forst things I had to buy in 1980 or so was an alarm clock, a touch-me-2 by Morphy Richards, which is still working. So in 40 years that has done 320,000 hours?

An LED bench DVM is the height of luxury, you can actually see the digits! The early Solartron, Farnell etc meters are worth their value in gold. Some of these use the early displays made from dots, not a bar.
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Old 22nd Sep 2019, 10:24 am   #13
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Default Re: Your first experience with LEDs?

I used to work in the lighting trade a number of years ago and i remember our first experience with LED outdoor lights especially ground sunk pavement units.
Very expensive and VERY unreliable , in fact we discontinued them for a while until the technology improved , which it did eventually.
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Old 22nd Sep 2019, 10:32 am   #14
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Default Re: Your first experience with LEDs?

Quote:
Originally Posted by duncanlowe View Post
It's amazing how the technology has changed. First the huge increases in light output, and more recently the massive reduction in If. I'd got so used to the value of resistors to give If=20mA at 12v and 5v that I never even calculated it. So when I was reviewing a design I immediately thought the designer had made a mistake with the resistor, given If would have bee just a couple of mA. See, still learning something new every day.
Some years ago I needed to 'buzz out' some telephone cable adapters. These had pins/contacts to fit different telephone sockets and a 6p4c socket to take a cable to a modem or whatever. I made a little tester with 4 LEDs wired to a 6p4c plug, series resistors (1k I think, to give a bit under 10mA LED current) and a 9V battery. The other side of the battery went to a test probe. I could thus plug the tester cable into the telephone adapter, probe the plug pins and see what LED lit up.

Well, the colours of the wires in the cable commonly used on 6p4c plugs are red, yellow, green, black. The first 3 went to traditonal, old, LEDs of the same colour, the last to a white LED. The first 3 were fine, but the white LED was so bright I didn't want to look at it for very long.

White LEDs give a visible glow on very low currents. Take such an LED and a 9V battery (PP3 type). Hold one wire of the LED in one hand and touch the other wire on the appropriate terminal of the battery. Now complete the circuit by touching the other battery terminal with a finger on your other hand. I got a noticeable glow from the LED doing that (not bright but I could certainly tell it was on), even though the current was <1mA, probably around 100uA.
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Old 22nd Sep 2019, 10:34 am   #15
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Default Re: Your first experience with LEDs?

Early '70s- I acquired an unknown type red LED in a TO72 type package with a clear lens top. It glowed (dimly) for years poked through the front of the same small cardboard box that served as a case for an old electromechanical accessory car clock that used a single 1.5V cell for its power.

That was the only use I had for it! It was just a novelty at that time.
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Old 22nd Sep 2019, 10:37 am   #16
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Default Re: Your first experience with LEDs?

First memorable one was paying 9 for a white LED and instantly blowing it up
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Old 22nd Sep 2019, 10:55 am   #17
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Default Re: Your first experience with LEDs?

Quote:
Originally Posted by Richard_FM View Post
I remember there was an early electronic game called Flashpoint which was a hand me down to me & my brother. The design of it was 1960s-70s.

It was a matrix of holes & a small jack plug on a cable, along with 3 LEDs indicating an arrow.

I can't remember the exact rules of the game but the jack was inserted into a hole an LED would light up to indicate in which direction the jack should be moved.

Eventually the jack cable broke & not having a soldering iron to fix it meant it was binned.
I have a few early electronic LED games myself including one called Blip from about 1976ish which even had a windup mechanical timer as i recall.
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Old 22nd Sep 2019, 11:20 am   #18
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Default Re: Your first experience with LEDs?

For donkey years car owners had to put up with the very fickle contact point ignition system which needed regular attention if you were not going to be stranded in the winter..

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.
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Old 22nd Sep 2019, 11:28 am   #19
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Default Re: Your first experience with LEDs?

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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 have been quite astonished of late at the "fade rate" of blue LED's. We had large blue LED clocks installed in our operating theaters where I perform cataract surgery, all synchronized to a master source. The segments are about 5" tall. Many of these have faded over only 18 months. I also installed some commercial mains energy consumption meters with blue LED's which have faded, in some segments, not others, over a 2 year time frame. It is disappointing, however it is not universal, some LED's appear quite resistant to the fading effect and maintain good light output, over many years with the same operating current.
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Old 22nd Sep 2019, 11:51 am   #20
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Default Re: Your first experience with LEDs?

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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.
They didn't really have to put up with that for long. By the late 60's many cars which had contact breakers had added ignition amplifiers which only ran 70mA via the contacts into a resistive load and there was no arcing at the contacts so the contacts then lasted for donkey's years.

Quickly contact breakers were gone and a magnet and a reluctor system was fitted. Not only did this eliminate contact breaker issues , but it allowed something else very special; the reluctor signal contained not only frequency/timing information but also amplitude information, because the signal amplitude from an AC generator (the reluctor) is proportional to the rotation frequency. This allowed the accurate computation of dwell which is not as well done if you just have frequency information from a contact breaker, optical sensor like Lumignition, or a magnetic Hall sensor for that matter.

This is an ill understood area of automotive ignition systems. If you just have distributor cam angle position (from a contact breaker, optical sensor, magnetic sensor) you can only fudge the dwell correction with a CPU program attempting to anticipate the required dwell.

It is not nearly as good as a reluctor pickup (which is everlasting and no maintenance) which can be processed to give uniform spark energy over the full rpm range with dwell correction intrinsic to the design. So Lumignition, is no better than an electronically assisted contact breaker, or a Hall device pickup for that matter.

Motorola recognized these issues and created a special IC for the task, the MC3334, to process reluctor signals. These are the basis for GM's HEI module.

Also, Lucas, who had a lot of difficulty with some of their early electronic ignitions, installed the HEI module, for these reasons, inside their AB-14 amplifier module fitted to many British cars including Jaguars.
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