Your first experience with LEDs?

[jjl]

The prototype of a system I worked on in my first proper job in 1984 used a blue LED along with red and yellow to indicate the colours then used to denote each phase of 3 phase mains supplies.
If I remember correctly, the red and yellow LEDs cost a couple of pence each whereas the blue LED cost at least £10.
I believe that the blue LED must have used quite a different manufacturing process to current blue LEDs as it was quite dim, had a poor viewing angle and had a Vf of about 4 volts and required at least 20mA to give acceptable light output.
Unsurprisingly, when this system went into production, the blue LED was gone. Coloured circles on the front panel were used instead, each with a red LED at its centre.

John

[Hybrid tellies]

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.

[russell_w_b]

Originally Posted by jjl

If I remember correctly, the red and yellow LEDs cost a couple of pence each whereas the blue LED cost at least £10.

Back in 1990 I Had a VW Polo that had a mixture of red, yellow and green LEDs for the usual dashboard cluster indications. The 'Main Beam' indication was what I thought to be a blue LED but was actually an incandescent lamp dressed up to look like a blue LED.

I understand this was because of the costs of blue LEDs.

[chriswood1900]

Mine was 1973 when I purchased a Rapidman 801 calculator with the small red led digits. It cost just over £40. This was followed in 1975 with a Commodore Scientific one.
Chris

[kalee20]

Originally Posted by jjl

I believe that the blue LED must have used quite a different manufacturing process to current blue LEDs as it was quite dim, had a poor viewing angle and had a Vf of about 4 volts and required at least 20mA to give acceptable light output.

John

Blue LED's are based on silicon carbide, whereas red, green, yellow are based on gallium arsenide, gallium phosphide, gallium whatever. So yes, different materials and different processes. But I don't know much more about details!

Originally Posted by russell_w_b

Back in 1990 I Had a VW Polo that had a mixture of red, yellow and green LEDs for the usual dashboard cluster indications. The 'Main Beam' indication was what I thought to be a blue LED but was actually an incandescent lamp dressed up to look like a blue LED.

I understand this was because of the costs of blue LEDs.

Yes I can remember the Polo's instrument cluster, 0.2" LED's generally, but the main beam indicator a filament bulb dressed-up with a cover to look like a LED.

How times change - now, we go into a hardware shop and see LED's dressed up as filament bulbs!

[cmjones01]

Originally Posted by kalee20

Blue LED's are based on silicon carbide, whereas red, green, yellow are based on gallium arsenide, gallium phosphide, gallium whatever. So yes, different materials and different processes. But I don't know much more about details!

Very early blue LEDs were based on silicon carbide, yes, and had huge forward voltages (up to nearly 10V in some cases). However, the current generation of blue LEDs, which are much cheaper, and upon which white LEDs are based, use gallium nitride as their material. It's much easier to work with than silicon carbide, I think.

Chris

[TonyDuell]

Talking of the cost of LEDs in the early 1970s, the HP9800 series of desktop calculators had LED displays (45 7-segment digits on the HP9810, 16 7*5 dot matrix characters on the HP9820 and 32 of said dot matrix charcters on the HP9830). These were all scanned by the processor/firmware so if the processor crashed it would have been possible for one digit/column to be stuck on which would probably burn out some LEDs. As a result HP added a monostable circuit on the display board so that if the drive line was stuck asserted for too long (the processor had crashed, etc) the display would be blanked in hardware. It would not be worth doing that now, but back then LEDs were expensive enough to be worth protecting.

The HP9830 has a power-on indicator (the other machines don't) and it's a filament bulb still. I guess it was cheaper than an LED.

[Radio Wrangler]

The 9825 had a single row of alphanumeric dot matrix characters. Overall, a very neat machine. A Mr Wozniak had been involved in its development.

The origin of the family, the 9100A wrote 3 rows of digits on a small CRT. All discrete transistor, diode and core memory.

Eeee them were the days.

David

[TonyDuell]

Going off-topic for a moment...

The 'How they do dat book' is now on Bitsavers. This is a technical description of the processor multi-chip module in the HP9825, etc and has joking cartoons in it. Worth reading for that alone.

Being very pedantic, the HP9100 has ICs in it. 8 op-amps on the magnetic card reader board. The rest of the machine is discrete transistors (and an amazingly low number -- 42 in the 9100A and 43 in the 9100B of flip-flops), diode gates, core-on-a-rope ROM for the microcode, core memory, and an inductively coupled PCB ROM for the main firmware.

Getting back to LEDs, multi-colour LEDs with a red and green diode in the same package and 3 connections were common. But similar multi-colour 7 segment displays were not (I never saw one, did they ever exist?). I would have thought that a display that was normally green but turned red on an out-of-range value would be useful in some systems.

[Biggles]

I remember getting my first LED to play with around 1980, when I was at school. Strangely it was a yellow one. Anyway, it kept me entertained for a few days and I think I finally installed it in my KB Junior transistor radio as an "on" indicator. I still have the radio in good condition apart from the regrettable 5mm hole in the front panel! Eventually my pocket money stretched to a 7 segment green display which I connected to a 7447 driver and 7490 BCD counter/divider TTL chip. My first venture into logic. I was easily amused in those days but I suppose around that time it seemed like cutting edge technology.
Alan.

[russell_w_b]

Couple of adverts from November 1975 to put things into perspective. Couldn't find LCD watches advertised in my Practical Electonics collection for that year.

[G6Tanuki]

Originally Posted by russell_w_b

Couple of adverts from November 1975 to put things into perspective. Couldn't find LCD watches advertised in my Practical Electonics collection for that year.

"Shopertunities" - ah there's a name from the past!

[Biggles]

I remember those LED watches. For some odd reason, my Dad bought one for my Gran back in the day, but she struggled with the button to get the display up, then she couldn't see the little red numbers properly. She still wore it though. It's probably still in a box somewhere. They must have been pretty battery hungry, although I expect the display would be multiplexed to save power, just like those old Texet? calculators the better off kids had at our school in the late seventies. And everybody thought it was stupendously funny to write upside down words using the display.
Alan.

[Techman]

I've been having a look for my old calculators and found my old Texas TI-30. It's in a bit of a state, but still works with a battery installed, although it looks like some of the key contacts are now a bit dodgy. I think I've got a couple of even earlier calculators boxed away in a cupboard.

[kalee20]

Originally Posted by cmjones01

Very early blue LEDs were based on silicon carbide, yes, and had huge forward voltages (up to nearly 10V in some cases). However, the current generation of blue LEDs, which are much cheaper, and upon which white LEDs are based, use gallium nitride as their material.

Thanks for correction, Chris! I'm obviously a bit behind the times!

Originally Posted by TonyDuell

Getting back to LEDs, multi-colour LEDs with a red and green diode in the same package and 3 connections were common. But similar multi-colour 7 segment displays were not (I never saw one, did they ever exist?). I would have thought that a display that was normally green but turned red on an out-of-range value would be useful in some systems.

I doubt if that is feasible. Bi-colour LED's have two chips, side-by-side, connected in inverse parallel. I believe the different colours are down to the crystal material, not just the doping - so it would be horrendously difficult to produce a single-chip, two-colour thing.

Given that, getting the 7 segments twinned, each segment pair side-by-side, would be a big packaging challenge. It's more likely to be feasible with VFD's than LED's.

[Herald1360]

Originally Posted by Biggles

I remember getting my first LED to play with around 1980, when I was at school. Strangely it was a yellow one. Anyway, it kept me entertained for a few days and I think I finally installed it in my KB Junior transistor radio as an "on" indicator. I still have the radio in good condition apart from the regrettable 5mm hole in the front panel! ...........

Alan.

You could fill the hole with a modern high efficiency green LED- a mA or two should suffice to light it brightly enough.

[Biggles]

One day I might get round to filling the hole! At the moment the radio sits staring at me every day from a shelf in the shack, reminding me of my youthful misdemeanor. It's actually an ITT-KB Junior. I forgot about the ITT bit. Now that's an interesting combination. Modern hi efficiency LEDs are a marvel compared to the original ones. I remember you needed about 20mA to light the old ones brightly. The LED probably drew more current than the radio. You only need microamps to produce visible light from some LEDs nowadays. I think the novelty solar garden lights must use hi efficiency LEDs as they seem to light a long time on a minimal charge from the postage stamp size solar panels. I remember that multi digit LED 7 segment displays were often multiplexed to reduce battery consumption. You could see a slight flicker sometimes.

[Reelman]

My first LED watch came from a friend around 1975, he got it off a Russian seaman as he was in the timber importing trade and worked at the docks at the time. Still have it somewhere.
I must have been familiar with LEDs whilst still at school as we had an electronics club. Later, I remember asking the engineer who came to repair our Borroughs TC500 terminal in November ‘74 at my first job why it used bulbs instead of LEDs. The TC500 was a device that you sat at and had a long row of small incandescent indicators above the keyboard. It also got very hot and had an oil sump! No display but two printers sharing the same carriage and programmed by paper tape. I see to remember his answer was “why, what’s wrong with bulbs”. Bought a LED calculator from Dixon’s in Birmingham the same month, not that I ever used it much but it was desirable new technology.
I’m sure one of the reasons why LED watches became a “must have” was a TV advert in the early 70s for Rothmans fags which featured a pilot pressing the button on his watch before taking off. It showed a lifestyle most of us could only dream of.... but we could at least have the watch!
I did connect a LED to my variable voltage supply and slowly increased the voltage to see what would happen. It lit, got brighter and brighter and then became dimmer and dimmer finally going out, never to light again. At this point I dropped it as it was burning my fingers... and an interesting hot plastics smell!
I didn’t progress to a LCD watch until 1978 when my girlfriend (now wife) bought me a Casio from Curry’s in Stratford as a birthday present for £56. Then for Xmas 1980 Dad bought me an Olivetti Logos 9 LCD calculator which, at the time was the worlds smallest printing calculator and not officially released until the following year.

Great times.

Peter

[ChristianFletcher]

I remember having one of those 100 experiments electronic kits with the spring terminals that you could hand wire into different projects. I remember the kit makers were very proud of the very dim red LED the provided in their kit. From memory is also had a ferrite rod and a meter and a few transistors. Happy days

I have a drawer full of old dim useless LEDs amazing how bright the modern LEDs are today.

[cmjones01]

Originally Posted by ChristianFletcher

I have a drawer full of old dim useless LEDs amazing how bright the modern LEDs are today.

Old-fashioned dim LEDs are no more useless than old valves! Not so long ago I had to replace the gate indicator LED in a piece of test equipment from the early 1970s (A Tektronix 7D15 timer/counter). A modern bright LED would have looked totally wrong amongst the incandescent lights everywhere else on the instrument, but I found an equally old LED in my stock and it looks just right for the period, with no other modifications required.

Chris