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Forum Index : Microcontroller and PC projects : The History of Blue LEDs
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LeoNicolas Guru  Joined: 07/10/2020 Location: CanadaPosts: 479 |
Super interesting video about the history of the invention of the blue LEDs https://youtu.be/AF8d72mA41M?si=9fH00XhiTK0Nqdl8 |
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| Frank N. Furter Guru Joined: 28/05/2012 Location: GermanyPosts: 828 |
 Frank |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Leo, All, I remember back in the early ‘70s that we discovered (or we were saw it somewhere and proved for ourselves) that if you removed the lid off a BC108 transistor we could get a purplish glow from it. I am not sure what we did now, but it was most likely putting two of the legs across a 9v battery. At the time we only had Red LEDs (maybe green just came out) and they were terrible compared to today’s. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
Excellent! I was glued to that from beginning to end. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Leo, All, I remember back in the early ‘70s that we discovered (or we were saw it somewhere and proved for ourselves) that if you removed the lid off a BC108 transistor we could get a purplish glow from it. I am not sure what we did now, but it was most likely putting two of the legs across a 9v battery. At the time we only had Red LEDs (maybe green just came out) and they were terrible compared to today’s. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Fascinating story and such an appalling reward for that engineer who spent all his waking hours for so many years developing processes and science that resulted in his company making billions whilst he remained so poor. It has some hallmarks of why I left the company below. In a previous vocation at a mining analytical company there was a push to develop a Xanthate monitor for checking Xanthate levels in the floatation's tailings. The push was more for cost purposes rather than ecological health. The wavelength that provided the best results was around 300nm but usable results were still obtained using blue light around 400nm. I worked on the analyser which at its heart used a single 5mm Blue LED, bought in the early 1980s at a cost of ~$260 for each LED from memory, and the output light level was almost invisible in normal room lighting. I remember having mild palpitations to even apply a small current to the LED initially. The blue light was split into two paths, one went through a defined reference level of Xanthate the other through the sample to be measured, that way any degradation of reducing light flux was automatically compensated for. The project was eventually shelved despite quite good performance, as economical and market pressures took the company in a different & more financially rewarding direction. LEDs have made such astounding increases and inroads since those early days. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| TimD Newbie  Joined: 23/02/2021 Location: United KingdomPosts: 27 |
It works the other way round, too. For my school A-level project, I used 4 decapitated BC108s as cheap phototransistors in a machine I built, that read a phone number off a punched card and then mechanically dialled a rotary phone. It was pretty unreliable, but luckily one of the few times it actually read and dialled the number perfectly was when the examiner came round to inspect our projects  - Tim |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
Ah, you should have used an OC71 and washed it in meths to remove the gel from the junction. Or, on an early one, just scrape the black paint off the glass. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| TimD Newbie Joined: 23/02/2021 Location: United KingdomPosts: 27 |
Good grief Mick, the Frankenstein-esque lengths we'd go to, to save a few pennies  To be fair, I think the BC108s were reliable enough in themselves; the problem was more to do with my circuit design (CMOS ICs), and the challenges of reading a 4-bit code from a punched card as you slotted it into the machine. Come to think of it, I believe there were actually 5 BC108's... 4 for the large holes representing the number in binary, and 1 for a small hole to act as a strobe signal to latch each number into memory. |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Hi Tim, All, I remember using the BC108 as a light detector as well, but we did little more than lit a light/led, I can’t remember exactly what we did. We really only had 2 transistors to play with in those days, the PNP OC71 and NPN BC108. We did so many things in those days, I remember building my own breadboard (In its true sense, chunk of wood with screws to secure the wires to) version of the 555 timer (from the equivalent diagram) and it worked. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| zeitfest Guru Joined: 31/07/2019 Location: AustraliaPosts: 482 |
There were silicon carbide blue leds available, but they were very dim and quite expensive. I think I still have one (?!) |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
The phototransistor version (OCP71) was quite a bit more expensive than the ordinary one. :( Actually, if you mistreat an OC35 with a suitable hacksaw they are a bit photosensitive too. :) They also explode really well with a suitable high voltage high current supply while they are clamped in a vice.... (OOPS! Did I really say that?). Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| zeitfest Guru Joined: 31/07/2019 Location: AustraliaPosts: 482 |
Once I misconnected an experimental pcb I made with a TQFP dsPic33. It got negative 12 v instead of 5...I wondered why it wasn't responding. Noticed a small red light on the IC, initially thought it was some sort of LED...It was a small red-hot spot !!! Out of amazement i repeated it, after two more times it stopped (glowing, that is ). Tough little beasties. |
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