LEDs & Other Low voltage, Low power lighting

Ask and answer questions, share tips and resources for installing lighting and other electronics in your models.

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LEDs & Other Low voltage, Low power lighting

Post by Sparky » Tue May 23, 2006 7:10 am

Here's a place for LEDs and other Low Voltage and Low Power lighting tips.
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Post by en'til Zog » Mon May 29, 2006 4:32 pm

Here's some basic inflamation about LEDs & such....


We’ve come a long way from lighting our models with fragile hot little light bulbs. Now most of us are using LEDs, Light Emitting Diodes. Little crystals sealed into epoxy bubbles or bricks that emit light when goosed by an electric current. The current LEDs are neat, but with technology there are always neater things under development. These are some of the neatest, newest lighting gadgets for modelers.

LED light emission is generally compared to candles - or candlepower. One candle puts out one candle power (Cd) , or 1000 milliCandella (mCd). A ‘bright’ LED puts out about 1 candle power or 1 Cd, or 1000 mCd which is hard to look into. JAMECO electronics (www.jameco.com) has many “superbrightâ€￾ LEDs including a nice 5000 mCd WHITE for $0.99 @ qty 10 - their part # 320531. They also have some very bright red/orange LEDs - 4.6 Cd at 2.3 volts 20 mA, 5mm, and $0.59 US in quantity 10, part # 197683.

ALL electronics (www.allelectronics.com) has a nice bright 1 Cd BLUE LED that goes for $1.50 (Qty. 10) which is nice for mass blue lights - LED-86. They also have a great pure RED LED with a VERY even field of light 2.2 Cd at 2.4 V 20 mA 5 mm Dia. and going at 3 for a buck US - LED-43. And of course, lots of other LEDs including a good assortment of self flashing ones, cheap.

Another good source of superbright LEDs is - www.superbrightleds.com. They may have the best commercial prices for the brightest standard LEDs.

A new (to me) company - ETG - has a really neat new product - a ‘smart’ LED. It contains 3 actual LED crystals, one Red, one Green, one Blue. That’s the RGB triad that gives color monitors all those colors. And a teeeeny microcontroller chip that runs them through an array of blinking, flashing, and mixing of colors to give a real rainbow of light - 3 V 95 mA 5mm Dia. for about $3.00 US. They also have a good selection of their own BLUE and WHITE LEDs at good prices, and if a batch of ‘you’ get together for the price break they can come down to $1.00 US each in quantity 100 (ouch). They also have a very nice bright 6 Cd AQUA LED. That’s from ETG - A Technology Corporation - Lloyd Greenberg at www.etgtech.com.

Then again, the cheapest source of LEDs is Christmas Lights - as long as you get the LED types. Phillips has some nice strings of 70 LEDs in BLUE, GREEN, WHITE (maybe others) that can be disassembled easily. (FIRST cut off both plugs from each end of the string, THEN start removing the LED lamps from their holders.) Phillips uses 5mm LEDs in their strings. FOREVER BRIGHT uses 2 and 3 mm LEDs in their strings - but these are hard soldered in place and require the use of a saw to disassemble them. I've had a few failures of BLUE LEDs from Forever Bright - they seem to have minimal quality control since the intensities on a string of the same color tend to vary - but they are a good source of 2 or 3 mm LEDs. Just check and compare intensities if you need a matched set (brightness) of LEDs. Phillips probably has better QC.

For the REALLY intese folks, there is a new breed of LED that takes (for instance) 3.6 volts at one quarter AMP - 250 mA or 12.5 times more power than the usual LED. The good thing? 480,000 mCd or 480 candle power, typical. THAT’s enough to blind you, literally. These are designed for lighting purposes, and Special Effects use. They come in RED, GREEN, BLUE, AQUA, and even WHITE. They DO get warm, hot even, compared to ‘normal’ low power LEDs but put out a stunning amount of light. And a lot less heat than an equivalent incandescent light source. What are they? LumiLED STAR LEDs, costing about $12.00 US EACH. ZOT! NOT for the inexperienced LED flasher. Where to find these? Try the nice folks at www.theLEDLight.com. Oh, and there are brighter ones - 3 watt units ( 0.830 amps at 3.6 volts) and a super bright 5 watt unit. These DO NOT run cool - they generate heat, but they're still a lot more efficient than bulbs. And they come in colors!

ALL Electronics now has a nice assortment of 1 or 2 WATT LEDs, not Luxeons. The BLUE and WHITE and GREEN ones run about $ 11.50 each and the RED and AMBER ones run $ 8.00 each. These can be run at 0.360 Amps OR 0.720 Amps making them quite bright. And quite warm.

Pity we can’t include pictures here. Yet....



What does “Viewing Angleâ€￾ mean?

“Viewing Angleâ€￾ refers to the cone of light thrown out by a ‘clear’ LED. The ‘angle’ refered to is the angle from the axis of the LED (a line directly OUT from the center of the LED) to the edge of the cone of brightness thrown by the LED. So the CONE is actually TWICE the viewing angle WIDE.

A 15 degree viewing angle means that the LED throws out most of its light in a cone 30 degrees wide - like a spot light. Small spot projected on a far well.

A 30 degree viewing angle throws out a 60 degree wide cone of light.

A 45 degree angle gets you a cone 90 degrees wide - big spot on the far wall.

And a 60 degree angle... yeah.

OR...

When you have a 15 degree LED imbedded in a model, if you're more than 15 degrees off the axis of that LED - off to the side a bit - you won't see much light from the LED 'cause the light is focussed in a thin beam that you aren't looking into.

An LED with a 60 degree viewing angle can be seen to be a bright spot of light from a lot farther off axis - farther to the side.

A diffused LED will simply be a glowing blob of light from about any angle that's vaguely in front of the LED. But dimmer for the light it puts out because that light is smeared out over a larger area. OR, the more spread out a light beam is - from 15 to 60 degrees - the more spread out the available light from the crystal INSIDE the LED is. Or, thin beams seem brighter. IF you're in the path of the beam.

An easy question -- I read your post about LEDs with viewing angles. When I see models of the Enterprise with those lovely spotlights, are we talking about a 15 degree viewing angle? If so, do LED vendors sort their LEDs by viewing angle, or is this something the modeler does? I guess that's two questions. Hope that's ok. Zaphod

LEDs are manufactured in specific shapes - the end of the ‘bubble’ of epoxy the actual LED crystal is embedded in is a lens in effect and shape. Some LEDs are manufactured with a lens end that focuses the available light from the crystal into a narrow beam like a spot light - 15 degrees wide or sometimes less. Other LEDs are manufactured to spread out the light and/or be visible from a wide angle like 60 degrees. This information is usually supplied in the manufacturer's specifications. If not, or if you bought a random batch of LEDs, you have to check out the LEDs yourself and see how big a spot (or how small a spot) the LED throws.



The SUBTLE Approach

I’ve been working with LEDs for almost a third of a century. All this time I’ve been trying to find more powerful, more efficient LEDs, and in colors other than ‘LED RED’.

Well, now there are gazillions of types of LEDs available. I’ve just gotten in two “Luxeon Lumiledsâ€￾ that qualify for ‘flashlight’ status without question. Incredibly bright optical packages like a stack of 8 quarters. One is in BLUE.

So now super bright LEDs are available and we can make our models shine, glow, and blast with light.

BUT....

We can also make them shimmer, quietly.

One of my favorite pocket LED lights is a “PALâ€￾ light. The LED is always lit, at a very low level. A “Find Meâ€￾ feature. All night it shines a puddle of light on my bedroom ceiling. And the 9 volt battery that powers it lasts for about 2 years. TWO YEARS ON, constantly glowing away.

Which got me to thinking. Why not have a switch on an illuminated model? A “High/Lowâ€￾ switch. One between the LEDs and (say) ground that lets you select which resistor(s) you are using to limit power to the LED. In the ‘normal’ position, the LEDs would be fully lit - say running at 20 mA (milliAmps) each. In the other position, they would be cut back to 1 mA or even 0.1 mA for a nice quiet glow at night. In a room fully illuminated by full moonlight, LEDs lit to that level are quite visible, and take almost no power. Set the model to ‘glow’ for normal use - pretty at night. Set it to ‘stun’ for contests and showing off to visitors.

For most models with ‘static’ LED lighting (no flashy circuits) you can just run the LEDs to a multi-pole, double throw switch. One position would connect the LEDs to ground (negative) through the usual dropping resistor to protect the LEDs from burnout. In the other position the LEDs would be connected to ground (negative) through a much ‘larger’ or more resistive resistor to limit current flow through each LED to 1 mA or less. If you use a multi-pole, double throw “Center Offâ€￾ switch, it can serve as an ‘on/off’ as well as a ‘high/low’ control.

This high/low can even be used with a 4060 circuit - only run LEDs from between one output of the chip and ground. Have a single pole, double throw switch to switch the LEDs common ‘ground’ connection between a direct connection to the ‘negative’ side of the battery/power supply, or between a resistor connected to that ‘negative’ connection. So the LED goes directly to Negative, OR go to a resistor and THEN Negative to cut power consumption dramatically.

Our models don’t have to glare at people in the night. They can glow quietly. Be “onâ€￾ while drawing a negligible amount of power. Pretty, lit, with very very long battery life.

It’s an idea.


4060 chips - how many LEDs can you drive?

The 4060 chip is wonderful for driving LEDs. Mainly 'cause it doesn't deliver more current than any known LED can stand. EACH output from the 4060 can SOURCE or SINK only about 11 milliAmps - can only deliver 11 mA in either a POSITIVE or a NEGATIVE state.

Now, you can drive several LEDs in SERIES from one output as long as the total voltage the series string needs doesn't exceed the voltage you're supplying to the 4060.

EXAMPLE: you drive the 4060 with 12 volts. You can drive a series string of 6 RED LEDs rated at 1.9 volts @ quite nicely, but not at full brightness (11.4 volts for the string). OR you can drive a series string of 3 BLUE or WHITE LEDs rated at 3.6 volts @ (10.8 volts total). BUT - each string will have only 11 mA flowing through it.

If all the 4060's outputs are lighting LEDs there may be some dimming if you haven't given the 4060 enough milli-Amperage to begin with. Say, 12 LEDs at 11 mA will need about 150 mA supplied to the 4060. Since I usually drive my circuits with a 9 volt battery with no current limiting to the 4060, I don't have a lot of trouble with dimming or power starvation. One circuit uses 3@ 4060 chips, and 60 or so LEDs - there is no noticeable dimming using one (rather stressed) 9 volt battery.

First suggestion? Get a cheap "Experimenter's block" or "Breadboard" and layout your 4060 circuit along with the LEDs you're trying to drive. The old engineering "Cut and Try" method. ALL and JAMECO have these boards for about 4 buck US.
Last edited by en'til Zog on Mon Jun 25, 2007 4:42 pm, edited 1 time in total.

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Post by tetsujin » Thu Jun 15, 2006 2:00 pm

En'til Zog wrote:Then again, the cheapest source of LEDs is Christmas Lights - as long as you get the LED types. Phillips has some nice strings of 70 LEDs in BLUE, GREEN, WHITE (maybe others) that can be disassembled easily. (FIRST cut off both plugs from each end of the string, THEN start removing the LED lamps from their holders.) Phillips uses 5mm LEDs in their strings. FOREVER BRIGHT uses 2 and 3 mm LEDs in their strings - but these are hard soldered in place and require the use of a saw to disassemble them. I've had a few failures of BLUE LEDs from Forever Bright - they seem to have minimal quality control since the intensities on a string of the same color tend to vary - but they are a good source of 2 or 3 mm LEDs. Just check and compare intensities if you need a matched set (brightness) of LEDs. Phillips probably has better QC.
It's worth noting that not all white LEDs are created equal. The older types, and perhaps the more cheaply produced ones made today, tend to be very bluish. This is because the actual LED component of a white LED is a single, short-wavelength color like blue or violet, which is then shifted to a variety of longer wavelengths with coatings of phosphorescent materials. Good, modern white LEDs give a much better white color effect. Christmas light white LEDs will generally be quite bluish. I think the average E-Bay white LEDs are much better, comparably priced, and don't require any work to get at the leads.
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Fiber optics and LED source

Post by bmagee » Sat Jul 15, 2006 8:07 am

I came across this site this morning while surfing the net. They have fiber optic strands/cable with multiple strands, LED's and lots of other neat stuff.

www.fiberopticproducts.com

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Post by Sparky » Mon Jul 17, 2006 12:59 pm

Yes they appear to be the only dedicate source of fiberoptics. some plastic company's carry fiber.

don't forget Neontrim for high voltage lighting sources
http://www.neontrim.com/
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Post by Sparky » Mon Nov 13, 2006 7:00 pm

<a href="http://www.kc6sye.com/2_wheresaneatpart.jpg" target="_Sparky">Is this plastic thingy on the counter a neat part?</a> <a href="http://www.kc6sye.com/1_casting_inprogress.jpg" target="_Sparky">Let's cast it.</a>

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Post by en'til Zog » Mon Jun 25, 2007 4:07 pm

Here’s an idea. You can use a 4017 to make a 10 LED array seem to ‘spin’ with one little dot running neatly around in a circle. If
that’s really what you want, fine. But how about making that circle of 10 look like there are 3 spots of light spinning around? Say,
in a Buzzard Collector? By using the ‘Persistence of Vision’ effect you can, and quite easily.

Normally you wire the outputs from the 4017 to the corresponding LED:

OUTPUT - 0 - 1 - 2 -
LED # --- 1 - 2 - 3 -

Note that these are the OUTPUTs from the 4017 - not the PINOUTs.

Try this:

OUTPUT - 0 - 1 - 2 -- 3 - 4 - 5 - 6 - 7 - 8 - 9 - 0 -
LED # --- 1 - 4 - 7 - 10 - 3 - 6 - 9 - 2 - 5 - 8 - 1 -

This technique gives you 3 apparent dots spinning around the circle of 10 LEDs. Try it. Diagram it first ‘cause this can be
confusing.

This technique works and works well - one of my favorite ‘tricks’ actually.

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Post by Sparky » Mon Jun 25, 2007 7:09 pm

Here's the ring diagram to go with the above rotating circle:
http://www.kc6sye.com/images/circuits/4 ... pinner.jpg
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Post by trekgeezer » Thu Jul 19, 2007 7:33 am

Check these guys out, they sell different sizes of LEDs along with wire and resistors.

They have the best prices I've found.


http://www.lsdiodes.com/
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Post by Sparky » Sat Oct 13, 2007 12:02 am

Here;s a note on diffusing LEDs:
Karim reports in another thread that:
Fiberfill can be used
This link is dead now sorry guys:(
http://karimnassar.com/assets/images/mo ... c/mc40.jpg


Another option is to choke the LED with a higher then needed resistor or lower then expected voltage source. The LED will dim down and you won't be fighting with the spot light it throws at full power. Add a few more LEDs in a cluster, all running under powered and you get a larger area of gentle light.

It's still cheaper than light sheet. Light sheet runs off high voltage so you have to wire accordingly, and has a noticeable limited brightness life.
Last edited by Sparky on Tue Jul 20, 2010 12:14 pm, edited 1 time in total.
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Post by kitty » Thu Apr 17, 2008 4:28 pm

If you need to light up windows in a model you could also use sidelight fibre optics with a bright led to get a diffused backlight as alternative to EL sheet or CFL tubes.
Everyone seems to forget that besides the usual end light fibre optics there also is sidelight fibre optics .
When you put a lightsource at one or 2 ends of sidelight fibre optics it wil distribute the light evenly along the length of the wire.
I use 9mm wire, although there are smaller and wider diameters available
When you bend the wire a lot or use a long piece, you use 2 lightsources.
For a straight piece of sidelight fibre optics of 12 inces long, 1 bright narrow angle led would suffice to get a fluorescent tube effect.
It is a bit more expensive then cfl tubes or EL sheet, but the advantage is that you can stick to low voltage/low current for the model.
And you don't get that irritating highpitched noise from a converter because you won't need one.
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Post by Sparky » Thu Apr 17, 2008 4:40 pm

Kitty, did the side light work for you? This is the stuff from fiber otpic products right. They warn on their site that LEDs won't work for this that you need the high power light sources (halogen bulbs).

I suspected that you get something from an LED for short runs of side light. . .
Please let us know what source you used for the sidelight fiber. I have some of the super thin Cold Cathode tubes, the regular CFLs stripped from the little portable fixtures, and plenty of LEDs. I'd like to do a side by side.
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Post by kitty » Thu Apr 17, 2008 4:50 pm

I use 9mm sidelight wire that i get from a dutch company www.ibgfiber.nl.
Its quite expensive about €60/mtr including tax
I don't know the manufacturer.
All i know is that it is enough to get a nice glow if i apply a single 5 or 10 mm bright white narrow angle led to one end of a 24 cm piece (the lenght of the warp grills of the 1/350 refit).
Or 2 super brights to a nearly complete circle of 30 cm diameter.
They usualy use several feet of the stuff to light interiors so a bright led is enough for less than 1 foot if not bended.
At least the stuff i got from that company.
The LEDS i use are quite bright though, like the light from a welding torch
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Post by kitty » Thu Apr 17, 2008 4:59 pm

Don"t forget that these highpower lightsources are meant for 50-80 foot lenghts for short lenghts you can suffice with a superbright led, they even sell LED light sources for it at fiber optic products (although they are for 12V).
BTW it's not solid sidelight wire i use
You just have to cut it exactly at a 90 degree angle and fix the wire.
I use like 1.5 cm length carbon tube with inner diameter of 9mm and epoxy to fix the wire approx .5 cm inside filling the rest and put in a 5mm led or 10 mm inner diameter carbon tube and epoxy to fix the wire and a 10 mm led.
I have some pieces of those tubes left from building kites.


BTW that was a fast reaction Sparky :)
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Post by Sparky » Thu Apr 17, 2008 5:36 pm

http://www.fiberopticproducts.com/sideglowcable.htm

Has
3mm @ $2.85/foot US
5mm @ 3.50/foot US
and on up

I have a sample of some of the thick stuff, they had a short length in the sale 'bin' on the web site. I'll try it out. I think if one factors cost of the cold cathodes tube, inverter, and brightness life, the LED and side light fiber is the cheaper way to go. I'll give it a try to see how it works up to the cold cathodes.
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Post by kitty » Thu Apr 17, 2008 5:43 pm

Not to mention the life of LEDs when you run them at lower currents and voltage so they light up less bright :)
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Post by Earnan » Tue Jul 15, 2008 7:16 am

Are there manufacturers or suppliers who offer a kit? I've done some searching, but with no luck.

I'd like to have one LED, a short length (10"?) of pre-attached wire, and the switch/battery case all in one complete box needing only to be taped or glued in place.

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Post by MillenniumFalsehood » Mon Sep 15, 2008 9:30 pm

I've seen a PL Enterprise with blue lasers for the phasers which produced a visible beam(a photographable one at least). Is there a red laser that'll do the same without burning holes in things?
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Post by jwrjr » Mon Sep 15, 2008 10:12 pm

The way to make any visible (not IR) laser beam is to have smoke, vapor, or some other form of particulate matter in the air. Without that the beam cannot be seen.

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Post by en'til Zog » Tue Sep 16, 2008 3:47 pm

To install a red laser beam in something, just 'gut' a cheap laser pointer. I see them around for $3.00 US - cheap!

Just buy one, take it apart, and see how the LASER crystal is mounted - one laser pointer/gooseneck LED light I dismantled has the crystal mounted on a small PCB that slips into grooves in the case... a bit tricky to use. Other 'normal' pointers have the crystal mounted on the main PCB along with the push button switch. A few (old old) ones have the crystal actually mounted in a little seperate can (TO-5?) which is great.

Then just feed the laser with 3.6 voltss or so - the voltage of a stack of 3@ 1.2 volt button cells.

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Post by Scott Hasty » Tue Sep 16, 2008 5:41 pm

Two things you have to be careful of when using bare laser diodes (besides it being an eye hazard when excited).

1) Most require a heat sink for extended use.

2) Not sure of the newer diodes, but the older ones needed circuitry to stabilize the input voltage (even when battery powered).

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Post by macfrank » Tue Sep 16, 2008 7:09 pm

At my old job, I made a 2D laser array for an experiment. I used 45 laser diodes that I hacked apart. We bought over 50 of them from American Science & Surplus.

The quality varied. The older laser diodes had epoxy PCBs and the boards were masked. The newer ones were on cheap paper PCBs (epoxy impregnated) and were shoddily constructed.

Typical construction of a laser diode:
The head, where the bullet shaped nose screws onto is typically made from metal-plated plastic. This head acts as a heatsink for the laser diode, as one of the power terminals (V+, IIRC - don't trust me on this) and as a holder for the collimation and focus lens.

This head is sometimes friction fit, sometimes epoxied onto the end of the PCB, where it clamps onto a wide pad. Removing the head will expose the bare laser diode chip and its tiny lead... I killed a couple of diodes just by taking the head off and accidentally touching the lead (and breaking it off). The chip is on its side, since the diode lases along the sides of the chip, not the top or bottom (which is soldered or epoxied onto a pad).

After the diode and the pads for power and heat dissipation, there's usually a small surface current limiting resistor. This will go to a pad under the power switch. The other side of the switch goes to a pad at the end of the PCB, where a battery contact spring is soldered.

There's always a small clear plastic cylinder inside the laser pointer that holds the batteries and insulates the positive side from the negative center. The cylinder has a hole in the bottom and that's where the spring contacts the negative side of the first battery. The screw-on lid touches the positive side and the case of the laser pointer, which in turn contacts the laser head. When you press the button, the circuit is closed.

If you're going to use a laser pointer in a hobby application, you have to be very careful of a few things:

1 - Somehow figure a way of soldering into the plastic heatsink/head. It can be done. I ended up wrapping 30 gage Wire-wrap wire around the head, then using a very fine tip soldering iron, I melted some of the wire into the plastic, to keep it from unraveling. You can't do it to the full length of the wire because the plastic isn't conductive - only the outer coating is.

2 - If you put too much power into the laser diode, it'll be damaged and will never be as bright as before. Never try to bypass the current limiting resistor, even when using only battery power (3.6 - 4.5V)

3 - if you remove the head, you have to be very careful with the lead to the diode. It is extremely fine and delicate and if broken or touched, the diode will not work. If you manage to operate the diode without the protective head, you'll need to find a heat sink that doesn't touch or damage the lead.

Geez, after typing all this, I found a picture online.

Frank

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Post by en'til Zog » Thu Sep 18, 2008 2:36 am

What he said. Listen to the Voice of Experience!

I plan to! :D

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Post by severedblue » Thu Jan 06, 2011 7:38 pm

Looking for a source of 0402 SMT LEDs as mentioned in this thread:
http://www.starshipmodeler.net/talk/vie ... hp?t=86200

Trawling the suggested links it's hard to find the text string "0402"

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Post by Sparky » Fri Jan 07, 2011 2:26 pm

Last time I went to order some SMT LEDs I was annoyed to find digikey out of stock on most of the ones I wanted to try. So I found out you can order direct from one of the companies:

http://www.kingbrightusa.com/

They're in the us so shipping was pretty fast. Best to use solder paste with SMT LEDs and a heat gun to melt the paste, BTW.
<a href="http://www.kc6sye.com/2_wheresaneatpart.jpg" target="_Sparky">Is this plastic thingy on the counter a neat part?</a> <a href="http://www.kc6sye.com/1_casting_inprogress.jpg" target="_Sparky">Let's cast it.</a>

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Underlord
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4060's found

Post by Underlord » Thu Aug 25, 2011 2:33 pm

I've heard that CD4060B's are hard to find. Digikey has them back in stock. Their stock number is 296-2060-5-ND. I ordered 25 of 'em for $9.54. I hope that'll be enough to hold me... I start my first lit model next week!
Your mileage may vary, void where prohibited, if it lasts more than 4 hours, see a doctor. All prosecutors will be violated. Only fools are certain. Substantial penalty for early withdrawal. The best advice I ever received was "Don't take anyone's advice. Listen to what everyone says, then make up your own damned mind."

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Post by Blappy » Mon Oct 29, 2012 12:15 am

I have a circuit with two blue LEDs from Radio Shack (Called The Source in Canada now) wired in series to a switch and a 9V battery. They are super bright right now.

Here is a video of it.
http://www.youtube.com/watch?v=WcPJMnKPfOs&feature=plcp

Am I giving these things too much voltage and will they burn out quickly? If I need a resistor in there what should I use to extend the life of the LEDs but still get decent brightness?
Greetings Programs!

"In the universe, space travel may be the normal birth pangs of an otherwise dying race. A test. Some races pass, some fail."
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Our only chance of long-term survival is not to remain lurking on planet Earth, but to spread out into space.
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Post by severedblue » Mon Oct 29, 2012 12:19 am

Am I giving these things too much voltage and will they burn out quickly? If I need a resistor in there what should I use to extend the life of the LEDs but still get decent brightness?
What are the part numbers / datasheets of your two blue LEDs?

You need to check that you're not exceeding the maximum forward current on those devices

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Post by brt » Mon Oct 29, 2012 12:24 am

Assuming the LEDs run with 3.2 to 3.4 volts each and require the typical 20 milliamps, the results below are what a program came up with. You will burn them out without a resistor

Supply Voltage
9 VOLTS
Voltage Drop Across LEDs
6.6 VOLTS
Desired LED Current
20 MILLIAMPS

Calculated Limiting Resistor
120 OHMS
Nearest higher rated 10% resistor
150 OHMS
Calculated Resistor Wattage
.048 WATTS
Safe pick is a resistor with
power rating of
.08 WATTS

http://ledz.com/?p=zz.led.resistor.calculator

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Post by Blappy » Mon Oct 29, 2012 8:21 am

OK. I sort of get it. SO based on a chart like this
http://www.elexp.com/tips/clr_code.gif

What colour coded resistor do I need? I have a pile (literally) here of them I got from my brother years ago when he quit electronics to take computer sciences instead.
Greetings Programs!

"In the universe, space travel may be the normal birth pangs of an otherwise dying race. A test. Some races pass, some fail."
- Robert A. Heinlein


Our only chance of long-term survival is not to remain lurking on planet Earth, but to spread out into space.
- Stephen Hawking, 2011

The Blaposphere

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