Sourcing UV integrated resistor leds - Page 1
Forum section: electronics / beginners

author: dalpets
author_rank: Contributor
timestamp: May 29, 2014, 06:33:36 am
content: Hi,I've scoured the internet for these 'bad boys' but haven't been able to find an online supplier.Does anyone know where I could pick them up on-line?Thanksdalpets

author: theatrus
author_rank: Frequent Contributor
timestamp: May 29, 2014, 02:20:58 pm
content: True UV LEDs are rather pricey (Rebel UVs are $15-30 each depending on wavelength and bin) - resistors are much cheaper, though a CC driver is suggested.

author: sleemanj
author_rank: Super Contributor
timestamp: May 29, 2014, 02:49:05 pm
content: You are not being very specific! What is the intended usage? What size, what beam angle, what wavelength, why exactly do you want integrated resistors, and assuming they exist, what value do you want?Sent from my HTC Dream using Tapatalk 2

author: MrsR
author_rank: Regular Contributor
timestamp: May 29, 2014, 10:18:53 pm
content: Quote from: theatrus on May 29, 2014, 02:20:58 pmI just bought 200 5mm LEDS Wavelength is 395 to 405 and Mcd is 3000. Price was $10.54 AU. by Ebay.I already bought 200 a few months back.I am making a UV Positive Exposure rig to make PCBs.I am making them in rows of 3 with a 68 ohm resistor power supply is 12.5 volts and the LEDS are 3.4 volts.I ordered the extra 200 as I changed the design from single sided to 2 side exposure and by my calcs. it will take about 7 minutes for sufficient exposure.There are stacks of UV LEDS listed. If you want the correct resistor I can work it out for you. I will need the supply voltage and LED voltage and current. Just read the specs. before buying as you can get caught with the wrong ones pretty easily.ALL THE BESTRachael

author: M4trix
author_rank: Frequent Contributor
timestamp: May 29, 2014, 10:26:59 pm
content: Quote from: theatrus on May 29, 2014, 02:20:58 pmThat's why I still prefer cheap UV tubes over diodes.

author: janoc
author_rank: Super Contributor
timestamp: May 29, 2014, 11:09:37 pm
content: You can get UV leds for quite cheap off eBay. Probably not Rebels, but they work fine for the intended purpose. I have built an PCB exposure lamp like that with them no problem. There are even sellers that will bundle you a bag of matching resistors for free if you buy e.g. 100 LEDs.

author: janoc
author_rank: Super Contributor
timestamp: May 29, 2014, 11:12:52 pm
content: E.g. this store (I think this is where I have got the LEDs from):http://stores.ebay.fr/HK-LED-CENTER-STORE/5mm-UV-LED-/_i.html?_fsub=670244014100 5mm LEDs, $11, free resistors included.

author: sleemanj
author_rank: Super Contributor
timestamp: May 30, 2014, 02:00:29 am
content: Quote from: wilfred on May 30, 2014, 12:42:16 amMy first UV exposure rig was made by drilling 5mm holes and pushing leds through, that was too much work.My second one was made by etching led boards and soldering the leds and resistors on, that was also too much work, and too expensive.My current UV box's light source (and we are just assuming that's what he's doing) was built on a piece of cardboard with a frame of MDF. Painted black. Printed and taped the LED pattern onto it, used a noticeboard pin to poke holes for the legs of each led, and then just pushed em through. Parallel strings of multiple in series, a boost/buck converter to get a smidge more than the minimum fwd voltage of the series string, one resistor per series to set the current.

author: dalpets
author_rank: Contributor
timestamp: May 30, 2014, 05:46:57 am
content: Quote from: sleemanj on May 29, 2014, 02:49:05 pmFor a UV light box! I know what I want, just integrated. I'll decide the exact specs when somebody tells me if & where they are generically available online. That's all I want to know. I don't want to make a 'Ben Hur' exercise out of it, mate.See youtuber using them @@ 19mins30

author: dalpets
author_rank: Contributor
timestamp: May 30, 2014, 06:12:29 am
content: Quote from: wilfred on May 30, 2014, 12:42:16 amSpot on, mate. I've just finished making 2 strip boards with a total 0f 168 leds for a UV light box. What a PITA.This guy uses them @(@19min30s). I think he's in the UK. I suspect they are expensive. Haven't seen them anywhere online so they probably haven't caught on or they are a very esoteric component.

author: dalpets
author_rank: Contributor
timestamp: May 30, 2014, 06:20:37 am
content: Quote from: janoc on May 29, 2014, 11:12:52 pmYep, they supply resistors separately that match the led specs but they are not integrated into the leds are they?

author: Hideki
author_rank: Frequent Contributor
timestamp: May 30, 2014, 09:07:24 am
content: No, they are not integrated. LEDs with built-in resistors is a specialty item. Not very common. If you combine that fact with UV LEDs not being very common either, the chance of finding what you want becomes even more slim.Why don't you ask your source, "channelengineer" in the youtube video?With normal LEDs, connect as many of them as you can in series and run the entire string at a higher voltage. Then you only need one resistor per string, which should be easier to manage.

author: Psi
author_rank: Super Contributor
timestamp: May 30, 2014, 09:20:42 am
content: some of the china led online stores let you order custom leds.So i guess you could get them made with resistors inside.However you'd probably have to buy 1000 or more.

author: Melkor
author_rank: Contributor
timestamp: May 30, 2014, 09:37:09 am
content: It would not be practical for them to have integrated resistors as the value of the resistor would be dependent on the Forward Voltage of the LEDs and the voltage of the source you use to power them up.I don't like the "free" resistor plan. In my personal experience LEDs from ebay may have a different Forward Voltage from the one in the "specs". I suggest you buy the LEDs, measure the Forward Voltage and then make a simple calculation for the resistor value you need. Also in that box the distance between LEDs suggest a need for wide angle LEDs , the ones with 25 degrees view angle I don't think will work too well.

author: Psi
author_rank: Super Contributor
timestamp: May 30, 2014, 09:40:31 am
content: Quote from: Melkor on May 30, 2014, 09:37:09 amleds with built in resistors are pretty much always intended for 12v automotive use.Although i have seen 5V ones.

author: MrsR
author_rank: Regular Contributor
timestamp: May 30, 2014, 10:08:32 am
content: ELEMENT14 list LEDS in 1000 to 4000 lot strips with resistors incorporated.They come in a roll in different colours but couldn't find UVs plus they are very expensive.The addressjannoclistedLED center Storeis ON Ebay where I just ordered my batch of LEDS you could email them and see if they supply what you want. They list quite a few types so they may be able to help.I am using Perf Board it has the holes drilled with a Donut of copper around the holes. I solder the LED in then bend over the leg to reach the next LED in series cut and solder, not hard to do but a bit time consuming.HOPE THAT HELPS

author: mariush
author_rank: Super Contributor
timestamp: May 30, 2014, 10:28:12 am
content: I sincerely doubt those eBay leds are capable of 3000 mcd , but even if they do that, they're only 20 degrees angle.Farnell has some cheap uv leds, 180$ for 1000 pcs, 112$ for 500:http://uk.farnell.com/vishay-semiconductor/vlmu3100-gs08/led-ultra-violet-405nm-plcc-2/dp/2395945With 120 degree angle and and not diffused and they're only 3.2 x 2.8 I think you could fit quite a lot of leds and make the uv light more even..Add a surface mount capacitor or one of these for each led if you want to use different voltages :http://uk.farnell.com/on-semiconductor/nsi45020at1g/ic-led-driver-45v-0-02a-sod123/dp/1794973and it should fit into a 3.5 x 3.5 square (leaving some space so the leads won't touch) ... from there it's easy to do the math to figure out how many leds you need in an area.

author: sleemanj
author_rank: Super Contributor
timestamp: May 30, 2014, 11:56:34 am
content: Quote from: mariush on May 30, 2014, 10:28:12 ammcd is loosely speaking a measure of visible light to humans, UV and IR should by definition be 0 mcd. The 400nm-ish UV range can arguably be measured in mcd for the visible spectrum they emit, but it's still silly to do so.http://www.gizmology.net/LEDs.htmNarrow beam does have some advantages in making a tighter beam to achieve very high resolutions, but, after experimenting, it's not worth it IMHO, indeed, I run with a diffuser and still get down to 8/8 - so much for collimation.

author: sleemanj
author_rank: Super Contributor
timestamp: May 30, 2014, 12:00:57 pm
content: Now, if you really want to be lazy, you can buy UV versions of the self adhesive led tape. I remember seeing somebody build a box out of it a few years back but damned if I can find it since.It can be a bit tricky to find (at least, it can be tricky to find a seller who actually tells you the wavelength, to ensure it's actually around the 400 mark), and I think you will have to use something as a diffuser to get an even coverage because the distance between leds on the tape is not particularly friendly to make a compact unit from memory (my maths teacher always did say that trigonometry would come in handy for something one day!), but for easy of use you can't get much lazier, peel, stick, apply 12v.

author: dalpets
author_rank: Contributor
timestamp: May 30, 2014, 12:53:19 pm
content: Had a bright, straight forward idea (no pun intended) for testing the optimum separation distance between the artwork and my 10x60 cm upper & lower strip boards (84 leds each) for my light box. I'm thinking this might obviate the need of doing the maths for uv dispersion.The design of the boards is from an on-line working 'instructable'.I simply turned the room lights off and raised & lowered a board until I got a reasonably even dispersion of uv on the desk surface. That occurred at about 9 -10 cm. Is that a reasonable assumption for a hobby light box?My leds have the following specs;* Emitted Colour : uv/ purple* Size (mm) : 5mm* Lens Colour : Water Clear* Peak Wave Length (nm) : 390~395* Forward Voltage (V) : 3.2 ~ 3.8* Reverse Current (uA) : <=30* Luminous Intensity Typ Iv (mcd) : Average in 2000* Life Rating : 100,000 Hours* Viewing Angle : 20 ~ 25 Degree* Absolute Maximum Ratings (Ta=25°C)* Max Power Dissipation : 80mw* Max Continuous Forward Current : 30mA* Max Peak Forward Current : 75mA* Reverse Voltage : 5~6V* Lead Soldering Temperature : 240°C (<5Sec)* Operating Temperature Range : -25°C ~ +85°C* Preservative Temperature Range : -30°C ~ +100°CBTW: what is the best way to adhere reflective foil on the inside of the light box?Thanksdalpets (O/P)

author: sleemanj
author_rank: Super Contributor
timestamp: May 30, 2014, 02:07:28 pm
content: Quote from: dalpets on May 30, 2014, 12:53:19 pmDepends on your separation distance and half-viewing angle (the viewing angle is the spread over the mid-line, so 20' angle is 10' each side), the closer the leds are to each other, the less distance you require vertically, naturally.Trig will give you the minimum distance to the artwork (or if you pick a desired distance to artwork, will give you the maximum horizontal separation), but in short trial-by-eye is necessary to eliminate the bright spots directly above the leds.My current box has from memory 108 5mm leds in 9x12 alternate-row-offset-grid, spaced quite far (to cover an A4 page area), 25mm center to center, the frame is about 16cm to the glass (it's single side at a time rig), with a diffuser situated midway between leds and glass.

author: janoc
author_rank: Super Contributor
timestamp: May 30, 2014, 03:29:37 pm
content: Quote from: dalpets on May 30, 2014, 06:20:37 amNo, they are not. To be honest, I haven't seen a LED with integrated resistor, apart from some stuff intended for lighting purposes - and those are very expensive.It is way simpler to have the resistors separately and choose the right one depending on how many LEDs are you chaining, what voltage are you going to use, etc. Or use a constant current PSU. It is a lot more flexible than having a fixed resistor inside the LED.

author: janoc
author_rank: Super Contributor
timestamp: May 30, 2014, 03:37:37 pm
content: Quote from: mariush on May 30, 2014, 10:28:12 amI have used this instructable to build the exposure box (yeah, I am too lazy to calculate the angles etc.):http://www.instructables.com/id/UV-LED-Exposure-Box/It works a treat and the narrow angles are not really a big problem - you need many of those LEDs anyway to get a reasonably uniform illumination. Compared to the Farnell LEDs you have mentioned I could probably build several of those boxes using the much cheaper Chinese ones - and it will likely work the same for the intended purpose.Of course, for critical work I wouldn't rely on a rig like this, but then I would go for a proper light box using UV CFL tubes and not bother with LEDs. Or I would send the the board to be manufactured in a board house.@Melkor: The free resistors are a convenience, you don't have to use themI think they ship resistors calculated for 12V use, if I remember correctly, i.e. you buy 100 LEDs and they give you a roll of 100 matching resistors.The eBay LEDs are perfectly fine for hobby work.

author: theatrus
author_rank: Frequent Contributor
timestamp: May 30, 2014, 04:48:57 pm
content: I do wonder the uniformity you'd get out of a few high power emitters over strings of 5mm low-current LEDs.The Luxeon UVs are very efficient, yet tiny, and rated for up to 1A currents:http://www.philipslumileds.com/products/luxeon-uv

author: Mike S
author_rank: Contributor
timestamp: May 30, 2014, 05:49:13 pm
content: Quote from: theatrus on May 30, 2014, 04:48:57 pmI've had pretty good results using high power LED's. It'll expose a board in 35 seconds, but the box is probably about 3 times larger than then nice low profile designs that guys are making with the 5mm LED arrays.I'm using 2x LEDengin LZ-4 emitters (385nm) and 6x 1W unbranded LED's (390 - 405nm).

author: dalpets
author_rank: Contributor
timestamp: May 31, 2014, 11:51:15 am
content: Quote from: janoc on May 30, 2014, 03:37:37 pmIt's been a very long time since I've done trig, so I too would like to avoid it, if possible.Before I dive further into this project it gives me some confidence to know that you were successful with it.So, could you tell me what separation distance you used between the artwork & the led boards & what you consider to be the max size board you could expose with this arrangement?Were you able to establish exposure times for different size boards?Did you make any significant changes to the author's design?I must say I don't like the author's power rails setup. Too easy to create short circuits. I used individual raised pins from a male header strip with heat sink inter stages.Did you persist with the author's recommended & finicky smd type installation of the resistors, or did you install them instead on the led side of the board? I found that if you don’t follow the authors smd style install, but install the resistors through hole with short raised leads they tend to short curcuit against adjacent solder joints with handling.Thanks for any feedback.Regardsdalpets

author: dalpets
author_rank: Contributor
timestamp: June 01, 2014, 06:45:08 am
content: Quote from: Hideki on May 30, 2014, 09:07:24 amUnfortunately many of these youtube authors don't monitor their sites, so more often than not you can't get an answer

author: dalpets
author_rank: Contributor
timestamp: June 01, 2014, 06:56:12 am
content: Quote from: Melkor on May 30, 2014, 09:37:09 amWell that doesn't seem to be the case if this engineer can do it, it can be done, mate.(@19min30s)regardsdalpets

author: Zero999
author_rank: Super Contributor
timestamp: June 01, 2014, 02:04:27 pm
content: As everyone mentioned above, it's better to jut buy the LEDs and select the appropriate resistor value or even better, use a switched mode constant current source.As far as choosing the right LED is concerned. The mcd rating is meaningless with UV LEDS because it's the radiant intensity, corrected to allow for the sensitivity of human vision at different frequencies. Any pure UV source below 380nm will have an output of 0mcd because the human eye isn't sensitive to that wavelength.http://en.wikipedia.org/wiki/CandelaMost of the LEDs discussed in this thread aren't really UV but visible violet i.e. peak emission at 405nm. This will work for exposing PCBs, according to what I can find about photoresists 300nm to 450nm will work to some degree so you could even try blue LEDs but peak sensitivity occurs in the 350nm to 380nm region. Unfortunately LEDs are less efficient and more expensive at these wavelengths so violet (400nm to 420nm) may be give the best compromise between the sensitivity of the photoresist and LED efficiency/cost.http://www.dupont.com/content/dam/assets/products-and-services/electronic-electrical-materials/assets/DEC-Riston_GeneralProcessingGuide.pdf

author: SeanB
author_rank: Super Contributor
timestamp: June 01, 2014, 02:40:28 pm
content: Quote from: dalpets on June 01, 2014, 06:56:12 amThose are lamp assemblies, designed as a drop in replacement for a standards automotive wedge base lamp. They are not LED's alone, but a 10mm packaged LED with 2 68R 0.125W resistors soldered onto the LED leads, the other end of the resistors then being fed out of the moulded base and bent over to emulate the form factor and leadout of the wedge lamp it replaces. Horribly inefficient, but lifetime and power use a lot better than the incandescent lamp it replaces, with the caveat though of it now being polarity sensitive so not a universal replacement for the lamp it is designed to emulate.

author: janoc
author_rank: Super Contributor
timestamp: June 03, 2014, 09:14:21 am
content: Quote from: dalpets on May 31, 2014, 11:51:15 amI have built it on a eurocard-sized piece of stripboard, pretty much the same as the guy in the instructable.Re max size of the board - that depends a lot on the distance of the LED array from the board and exposure time. I haven't played too much with it, but I wouldn't go beyond something like eurocard with it - the lighting wouldn't be uniform towards the edges anymore. Small boards are fine.Quote from: dalpets on May 31, 2014, 11:51:15 amFor me it took about a minute to expose my board, at cca 25cm distance. However, that may no work the same for you - different LEDs and I am using the dry film negative resist (the foil that you laminate on the board). You will need to experiment.Quote from: dalpets on May 31, 2014, 11:51:15 amYes, the shorts were a problem, all it takes is a little solder bridge or molten insulation on the wires. However, the wiring can be done in various ways, it is not all that critical.Quote from: dalpets on May 31, 2014, 11:51:15 amI have put them "smd-style" as he did. I didn't have any shorts with them - just make sure you align the leads along the stripboard track before soldering & cutting, don't leave them "hanging over". Whenever I had a short somewhere, it was either a solder bridge between two strips on the strip board or a wire touching something it wasn't supposed to touch due to the insulation shrinking/melting somewhere.In hindsight it would have been easier to just use SMD resistors instead, but I had a bag of regular 1/4W resistors that came with the LEDs on hand.

author: dalpets
author_rank: Contributor
timestamp: June 07, 2014, 04:02:03 pm
content: Thanks Janoc for your reply.The Channel Engineer has replied & here's the long & short of it.Ultra Violet Wedge LED Indicator Lamp, 9mm Lamp, 10mm dia., 12V dcavailable fromhttp://uk.rs-online.comitem code 0336160 ( not exactly the one he used on youtube)This lamp has an integrated IN4148 diode for reverse voltage protection & the lamp has an integrated 450 ohm resistor for current limitingCheers