Smallest LED? - Page 1
Forum section: electronics / beginners

author: THATguy
author_rank: Regular Contributor
timestamp: February 04, 2017, 09:36:59 am
content: http://www.ebay.com/itm/5-pcs-LED-SMD-0201-red-30-105mcd-0-65x0-35x0-2mm-135-1-95-2-35V-/112273354598?hash=item1a24036f66:g:eGgAAOSw241YfxpDDrawing around 2 volts, seems quite high?I only need it for open air optical communication, do you think it would be okay if I gave it less voltage?Are these the smallest?I'll be fixing the LED to a tiny bit of optical cable to ensure a fixed output direction of the light.Can I use a tiny Selenium wire to make my own minute light source.I found these Optical Laser Diodes, but they're huge - they only draw 1.5v which is a bit better, but they're far more bulky.http://www.ebay.com/itm/0-5W-500mW-1064nm-Fiber-Coupled-High-Power-Laser-Diode-4PIN-with-FC-Connector-/271033640520?hash=item3f1add2648:m:mklMyTI0rn64MvNXhlEMtGgThe open air optical communication will be in a closed box, is air a problem for tranmission - should I instead use an inert gas or vacuum?My closed box will be dark, but it might heat up to 40 deg celcius. The distance of communication will be less than 10mm.Sorry if this is beyond the scope of this forum. I can always do some tests of my own and find out.

author: mariush
author_rank: Super Contributor
timestamp: February 04, 2017, 10:10:59 am
content: If the distance is less than 10mm , why not use a commonly available optical isolator or something like that... after all they're just a led and optical sensor inside.. same thing you want to recreate.From what you wrote, it's not really "open air" as you plan to guide the light through optical fiber ... so rather than doing that just find some optical isolator in a wider package, enough to spread over those 10mm and be done with it.

author: Twoflower
author_rank: Frequent Contributor
timestamp: February 04, 2017, 10:30:23 am
content: I can't comment to the LEDs itself, but I might give some thinking points to your application (even if I know little of it).If voltage is a problem you can go to IR. This is also widely used for communication purposes. Think about IR remote controls, but also most fibre optics work in IR. Not sure why they specified 650nm for SPDIF.Not sure what you plan to do. If you don't want to have any connectors for the fibres I would look for a SPDIF fibre (TOSLINK) as they have a huge active core (1mm). That make it easy to couple in and out enough light. But you might be careful with the type of glue you use. As the TOSLINK fibre is plastic and uses two different type of plastics (for the two refractive indexes) the glue must not solve the fibre.And for 10mm distance and 40°C is a very friendly environment. As alternative there would be, as you mentioned, using no fibre at all. For this short distance you don't need to take care about the gas in between. You see the light by your own eye, why should a detector not see it? But probably I would still use IR and a detector with a build in IR filter to reduce the impact of stray light to your communication. Also you might need to debug your hardware. And doing this in the dark might be tricky.

author: THATguy
author_rank: Regular Contributor
timestamp: February 04, 2017, 10:59:53 am
content: Optical Isolators seem quite bulky. And I need the transmistor to also be a receiver.Yes, I would ideally use IR light.Yeah, I guess my system will be in the dark - makes sense, I don't want any Light interference.It will be a kind of BUS communication between components.The reason I wanted to use a bit of optical fibre is to direct the light but also receive the light - without too much interference. The paths will be fixed, so maybe at such low levels it might not be an issue.I could try some other kind of dividers; graphite tube or maybe even obsidian tube (both very low profile).I was going to fix my light source into some kind of resin and machine the top flat to it would fit flush with the optical fibre, but you are quite right, there may be issues with different matericals.This whole thing might require some more thinking and digussing on physics forums.As for debugging - it will be a straight through BUS, so only really need to test transmit and receive.Transmit - get something that lights up in response to IR. (I've a Flir Thermal Imager, which may help).Receive - are the angles correct.Test either for transmit & receive when outside of my BUS housing.

author: wraper
author_rank: Unknown
timestamp: February 04, 2017, 11:08:11 am
content: Do you understand that LEDs are current, not voltage driven devices? Also what a nonsense by writing it "draws certain voltage", it draws current. If you artificially limit the voltage (in the region where the LED still emits the light), current (and brightness) will just rapidly decrease, and will became very unstable as tiny voltage change will affect the current a lot. Temperature will affect it a lot as well.http://www.learningaboutelectronics.com/Articles/What-is-the-forward-voltage-of-an-LED(except "since bright LEDs need more power to work." is not correct as it depends on technology LED was made with, not power)

author: Twoflower
author_rank: Frequent Contributor
timestamp: February 04, 2017, 11:29:35 am
content: Have you thought of using something like IRDA? There quiet small tranceiver modules available (like RPM871). They're meant for bidirectional communication and low power. Keep in mind that this module is not just a LED and a photo transistor, so check the datasheet first if this one would be suitable for your design.

author: Ammar
author_rank: Regular Contributor
timestamp: February 04, 2017, 12:19:36 pm
content: Quote from: wraper on February 04, 2017, 11:08:11 amYes, you are correct. But this is the beginners section so maybe go a little easy.

author: Ammar
author_rank: Regular Contributor
timestamp: February 04, 2017, 12:22:04 pm
content: If you are interested in how small LEDs can get, check out bare LED die.www.epigap-optronic.com

author: matseng
author_rank: Frequent Contributor
timestamp: February 04, 2017, 03:38:23 pm
content: You could mount the LED dies directly on the PCB as they did in this "samurai" wristwatch. When I took it apart I don't even see the LEDs at first, not until I ran my fingers across the PCB and felt something like grains of sand on it. But then it was too late already, I had severed several of the bonding wires. :-( So I had to spend another $3 for a new watch.... :-)

author: ebastler
author_rank: Super Contributor
timestamp: February 04, 2017, 09:34:55 pm
content: ThatGuy -- it would help if you could tell us a bit more about your actual application and requirements:What are you trying to achieve?Why is the small size of the LED required (while, on the other hand, you seem to have room for a dark enclosure, and were even thinking about a protective inert gas environment)?Is there a limitation on the available supply voltage, or why the initial concern about the LED's operating voltages?Without that background, it's hard to make recommendations.

author: THATguy
author_rank: Regular Contributor
timestamp: February 04, 2017, 10:06:27 pm
content: MatsengWOW! That, is what I'm after. Perhaps you can give me a link to ebay?Or do they do this on every Liquid Crystal display?EbastlerI just want to make a BUS between several chips. An experiment, then I'll take it further. I feel light is superior - speed & no interference from magnetics (while I still have the electrics behind the light BUS system, I would then try to eliminate the electrics at a future point).I want the small LED because I want more than one BUS communication path ways, I might only get 2 between each chip, but the more I can get the further I'll be able to scale it down.The only reason I was considering Inert environment is just aiming for the maximum clean light transmission - at small sizes interference could be a big problem.Now I know heat may be an issue and I'll keep that in mind.I want low power because it is more efficient, and at lower levels, you can harvest power (free energy!!!) Low power is better when the device is smaller too, and of coarse less heat (not from the photons but the electrics behind it).

author: ebastler
author_rank: Super Contributor
timestamp: February 05, 2017, 07:18:07 am
content: Quote from: THATguy on February 04, 2017, 10:06:27 pmHmm, I am not convinced. Optical signal transmission is used routinely, of course. But that's either over long distances (where the extra effort of converting to optical and back, and coupling into a fiber, is paid off by high bandwidth, low loss transmission over long distances); or over short distances, if galvanic separation is needed (for safety reasons or to avoid ground loops).But if I understand you correctly, you want to use optical signalling over short distances (millimeters or centimeters?), without either of the reasons I mentioned. In that situation I don't see the benefit.QuoteYes, crosstalk between adjacent LEDs would be a concern, if that's what you mean by interference. But how would an inert environment help with that? (Unless you use some opaque potting compound, which makes the device impossible to repair.)QuoteIf you are concerned about power, you need to look at the LEDcurrentstoo, not just the voltages -- but I trust that's clear. If you want to build low-power circuits, doing away with the whole optical bus idea and using plain electrical signals is the best solution by far

author: THATguy
author_rank: Regular Contributor
timestamp: February 05, 2017, 08:29:43 am
content: The reason I want to do this is to reduce heat. There will be air gap between chips with no Traditional BUS wires.The gap will be further cooled by heat sink. Heat reduction improves circuit performance.It doesn't matter, I'm doing it.I wasn't really thinking about cross talk as such, but yes, that is the end result of photons going astray.Well I figure an inert gas would give a stable environment (single element variable) for the photon's to travel in Vs a variable mixture of different elements in Air. There may also be Thermal advantages depending on what Inert Gas I pick.Yeah, I want everything be as low as possible, current and voltage.

author: wraper
author_rank: Unknown
timestamp: February 05, 2017, 08:32:26 am
content: Quote from: THATguy on February 04, 2017, 10:06:27 pm1. Light is not faster. Actually optical coupling will limit the data transmission speeda lot.2. Have you heard about devices called optocouplers? Because they are exactly what you are trying implement in ridiculous way.QuoteLOL what?QuoteUsing lower voltage LED is not lower power, exactly opposite, P = V * I BTW. Those old leds are much less efficient than newer ones. Also IR is more suitable than visible light for this.

author: wraper
author_rank: Unknown
timestamp: February 05, 2017, 08:39:38 am
content: Quote from: THATguy on February 05, 2017, 08:29:43 amYou better describe what you are trying to achieve in the first place. Because the way you are trying to implement it is some sort of nonsense.

author: ebastler
author_rank: Super Contributor
timestamp: February 05, 2017, 08:43:04 am
content: Quote from: THATguy on February 05, 2017, 08:29:43 amIf you need to send signals to and from a device that has to maintain a temperature very different from the environment, that could indeed be another reason for optical coupling. Say, a cryogenically cooled sensor inside a temperature insulating, transparent enclosure. (Edit: Thinking of a glass and vacuum Dewar or such). In that case, you would send the optical signals through free space, to avoid any additional heat-conducting wires.Not sure whether that is your application, and hence not sure whether I subscribe to the optical bus idea in your case. But never mind, I don't want to deter you. Sounds like an interesting technical challenge, and at the very least you will learn something!

author: ebastler
author_rank: Super Contributor
timestamp: February 05, 2017, 08:46:55 am
content: @Wraper, I have my doubts about this concept too. But please, let's keep in mind that this is the Beginners forum, and let's not be too abrasive.

author: THATguy
author_rank: Regular Contributor
timestamp: February 05, 2017, 10:17:03 am
content: Oh yeah, it looks stupid.But it's just an easy way to test it out, before getting more complex.That is the purpose, a BUS is the simplest light transmission 'circuit'It can be minaturised further, and scaled up (increase the BUS bandwidth), without fundamental changes to the design.I know optical communication is the the be all end all - there'll be problems forsure.It's okay that some of you might want to deter me - you're concerned I'm just doing something very impractical, I get that.

author: Twoflower
author_rank: Frequent Contributor
timestamp: February 05, 2017, 12:21:30 pm
content: Regarding your low power requirements:* The size of the LED housing or using the bare die does not matter! Because the piece that emit the light is the same. Check the voltage and current ratings (that's the power consumption). The LEDs with housing provide better optical gains (lenses and build in reflectors) so they will be more effective. Probably bigger LED dies might be also more efficient as the bonding does cover a smaller part of the optical area (if the LED die is bonded).* If you have a bus it is probably lower power to convert them first in a serial steam and use a single optical link.* If you reduce the LED power you might end up to need more power at the other end: Probably the receiver and amplifier needs more gain and better signal to noise levels. This may end up in a higher total power consumption. Probably there's a sweet spot between transmit power and receiver power.* Also keep in mind: Each photon not hitting your receiver contain pieces of your precious energy!If you insist to transfer your bus as is in parallel, you need to think about the mechanical challenge.Going through the air/gas/vacuum/transparent fluid: What's your available area on the transmitter and on the receiver? Can you focus each individual bus signal to an dedicated spot on the receiver without notable crosstalk?How precise you can reliable aim in the product during production?Using fibres: Mounting the fibres is a big challenge the industry is heavily working on. Especially kind of chip to chip. But so far there's no cheap option. Even for board to board only few options exist. Most of the solutions are niche markets for very high throughput (the only place it make sense). Like for PCIe, 100GE or backplanes for computer racks. For example the Avago MiniPOD (for example the AFBR-811VxyZ it contain 12 transmitter or 12 receivers, about US$320).You could use Pigtails to feed into a set of fibres. But these multi fibre cables are not easy to handle, even the multimode ones. OK, you could light up the whole area and hope the receiver receives some photons, but it wastes lots of your precious energy. Coupling in the light requires very precise optics and adjustment of fibre, optic and emitter/receiver.Still for prototyping: Have you looked into the TOSLINK fibre option? Or some light-guides. In the end that will be an opto-coupler which probably performs bad regarding the power efficiency. Why would a opto-coupler manufacturer design the thing to waste energy? They can design everything to be highly efficient, including the optical channel.

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2017, 07:03:17 am
content: After reading through this whole thread I still have no idea what it is that the OP is trying to do. Surely an opto-isolater would be a far simpler and superior choice? You can even get multiple opto isolators in a single IC.

author: ebastler
author_rank: Super Contributor
timestamp: February 06, 2017, 12:47:11 pm
content: Quote from: james_s on February 06, 2017, 07:03:17 amLooking at THATguy's other recent posts, he seems to focus on projects "off the beaten path" at the moment -- inductive heating, induction-based USB cables, building your own CPU...Maybe the optical transmission project ("optical BUS") is meant to be used in the context of a CPU design? As mentioned above, I also have my doubts about the concept. But I'm sure there is something to be learned from building a multi-point optical bus from scratch.

author: JoeN
author_rank: Frequent Contributor
timestamp: February 06, 2017, 08:52:01 pm
content: Quote from: THATguy on February 04, 2017, 09:36:59 amThree pounds per tiny LED and the guy can't even supply a decent picture. Wow. Do not encourage that idiot.http://www.digikey.com/product-detail/en/kingbright/APG0603SURC-TT/754-2024-1-ND/6072771P.S. Remove "?hash=item1a24036f66:g:eGgAAOSw241YfxpD" from ebay auctions when you post them. It's not necessary and who knows what that contains.