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Author Topic: interfacing 12x 1w LED  (Read 6791 times)
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was hoping to pick anyone's brain about the best way to wire up 12 x 1w LED's  (each one to its own output on the arduino board). I need led's with a fairly low viewing angle as they are going to be mounted into the base of clear acrylic pipes forming a 12 note colour organ - therefore I want there to be as least light bleeding between the different pipes as possible. I have been working on this project for a bit now and with the help of angry Mike and combatdave managed to get the midi side of the project working (i.e. being able to trigger individual outputs through a midi keyboard) I now need to wire in the correct brightness LED's, I was initially looking at other lighting options like 12v halogen bulbs and even PAR36 pin spots but none of them like being turned on and off repeatedly and both also have a short but noticable warming up and warming down period which would alter the desired effect i am looking for with this colour organ. LED's, especially the bright ones seem to be the ideal choice. I have come across these:

Description

    * LED, SMD, DOME, 6 X 6MM, 1W, WHITE
    * Colour, LED:White
    * Luminous Intensity, Typ:42000mcd
    * Angle, Viewing:60°
    * Current, Forward If:350mA
    * Voltage, Vf Max:2.8V
    * Temperature, Operating Range:-40°C to +100°C
    * Case Style:6mm x 6mm
    * Colour, Lens:Water Clear
    * Current, Peak Pulse:1000mA
    * Depth, External:6mm
    * Length / Height, External:4.8mm
    * Lens Type:Dome
    * Luminous Flux, Max:61lm
    * Luminous Flux, Min:39lm
    * Luminous Flux, Typ:52lm
    * Luminous Intensity, Max:65cd
    * Luminous Intensity, Min:39cd
    * Power Dissipation:1200mW
    * Temp, Op. Max:100°C
    * Temp, Op. Min:-40°C
    * Temperature, Storage Max:100°C
    * Temperature, Storage Min:-40°C
    * Termination Type:SMD
    * Voltage, Vf Min:2.2V
    * Voltage, Vf Typ:2.5V
    * Width, External:6mm

from farnell and they seem the ideal solution - what i was hoping to get some help on is what would be the best way to drive them? another forum post mentions using 2N2222 transistors for driving bright LED's - if I got 12 of those, would that do the trick? anyone have much experience with this kind of set up, is heat going to become an issue?

any help is very much greatly appreciated!
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Those LEDs need 350mA each, so 12 of them will draw 4.2A.  Better allow for a 5A power supply and 5A rated wiring!  The 2N2222 has a collector current rating of 500mA, so that's OK.  Watch out for the wattage rating of the series resistor (you will need 12 series resistors, one for each LED/transistor).
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Watch out for the wattage rating of the series resistor

Often LEDs of this power are controlled by a constant current supply rather than the traditional series resistor for exactly this reason.
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thank you for the replies, it all seems to be clear now (I think!), with regards to suitable series resistors - you mentioned i need to look out for correct wattage rating (in this case 1w), would these be suitable for the job:

RESISTOR, 1% 0R030
Power Rating:1W; Resistance:0.03ohm; Tolerance, Resistance:± 1%; Series:OARS; Temperature, Operating Range:-40°C to +125°C; Resistor Element Type:Metal Strip; Temperature Coefficient:± 20ppm/°C; Case;
found here:  
http://uk.farnell.com/welwyn/oar1-r030fi/resistor-1-0r030/dp/1200361

was not sure of what resistance they need to be in this situation - as there were a few options.

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Resistance:0.03ohm

NO.

Assume you power the LED from 5V and it takes a forward voltage of 2.2V that means you have to drop 5 - 2.2 = 2.8V across the resistor. If you want 350mA to flow through it then the resistor needs to be:- 2.8/.35 = 8R (8 ohms)
Plus you will need to dissipate:-
2.8 * 0.35 = 0.98 W
so a 1W resistor will get too close to the limit you are better going with 3W. This might need a heat sink.
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The best way to drive high-power LEDs is with a constant current source so that they don't burn up from thermal runaway and other fun things.  Many of them are designed to handle up to 700-1000 mA, but only if you are _really_ managing their heat properly.  They typically are rated at 350 mA.  In any case, you have to manage the heat or your LED will fail prematurely.  Also keep in mind that high power LEDs are available in WIDE viewing angles.  So to get a focused beam, you'll have to design that solution yourself.

I have been studying high power LEDs for the last few months for a project I'm working on (which is also what I'm using my Arduino for).  Here's the quick version of some info you may find useful:

LED drivers:
National Semiconductor's LM34xx line is very nice and uses a minimal number of additional components.  They also have an online tool called WEBENCH that takes in your req's and gives you the schematic, bill of materials, efficiency charts, and even lets you order the entire prototype.  For DIY stuff, sometimes the prototype boards are perfectly suitable.

http://www.national.com/analog

Linear Technologies also has a decent line of LED drivers.  They also supply LT-Spice, which is a pretty nice free SPICE app and many of their ICs are included with the program so you can design circuits with quality simulations of the Linear products.

http://www.linear.com/pc/viewCategory.jsp?navId=H0,C1,C1003,C1094
http://www.linear.com/designtools/software/

LEDs:
Cree's X-lamp series are the best available right now, IMHO.  They are very bright for the power and have excellent reliability.  I like the XR-E and the MC-E series, personally.

http://www.cree.com/products/xlamp.asp

Philips Lumileds Luxeon LEDs are probably the next in line:

http://www.philipslumileds.com/products/luxeon/

So far I've found all of these products at Newark.  In fact Newark sent me a promo catalog that targeted lighting, and thus high power LEDs, so that was an easy one for me  smiley

http://www.newark.com/

With the Arduino, you can use the digital IO pins to control on and off state and/or the PWM outputs to control the LED brightness via the driver ICs.  You can also monitor the temperature of the LEDs via the analog input pins and act accordingly - which is what I'm doing for my project.
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wow - thanks for all that information, you have obviously done a lot of research. The viewing angle of the LED's is a problem, however i have been able to find 1w ones with 60 degree viewing angle which i am hoping will create the desired effect. The heat is an issue which I am still yet to resolve - but if I understand you correctly if I order the correct LED with the appropriate driver this would be more manageable. Pardon my ignorance, but am I right to interpret your post as to suggest that rather then wiring up the LED to a transistor and a series resistor I could purchase a readily designed LED with built in appropriate driver to be able to wire up straight to the arduino board and an external power source?
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am I right to interpret your post as to suggest that rather then wiring up the LED to a transistor and a series resistor I could purchase a readily designed LED with built in appropriate driver to be able to wire up straight to the arduino board and an external power source?
If you could find such a thing entirely pre-made, it would be optimal.  But I doubt you will currently.  The high-power LED industry isn't quite that far up to speed. smiley-wink  The rest is accurate though.  You will need to buy the LEDs and either build your own driver circuits or order a prototype assembly from National Semi through their WEBENCH tool and see if it works for you.  The PWM output on the Arduino can control the LED dimming via the PWM pin on the LED driver IC.  And the digital IO can control the LED's on/off state via the on/off control pin on the LED driver IC as well.

Also, I highly recommend buying LEDs that are pre-mounted to a metal-core PCB because they are WAY easier to mount and manage the heat issues with, and you can get pre-made optics for them as well.  You will still need to mount them in such a way as to allow the heat to escape.  Newark/Farnell has these and some pre-made optics for a few of the more popular LEDs.

If you can't find colored LEDs that are pre-mounted, you can always put colored acrylic over the end of the tubes and use white LEDs.

(BTW: I have no special interest in Newark/Farnell.  They just happened to send me a catalog at an opportune time and they have pretty much everything I've needed so far at what appear to be reasonable prices.)

Glad I can help!
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hi - I am having some problems with translating this idea from the breadboard onto a prototype circuit board. The 2N2222 keeps blowing whenever I try to control the LED through midi. When I wire everything up on a breadboard everything works great - and then when i set it all up and solder into my prototype circuit board, everything seems to work fine also - i.e. the LED powers up when I run current through it, the problem arises when I connect the pins to the arduino board (pin 3 to GND and pin 2 to my digital output), as soon as I do this and try to control the LED through MIDI it blows the 2N2222. Does anyone have any suggestions why this may be? At first i thought it was my soldering but the fact that it works fine when plugged into the power transformer and the 2N2222 blows only when I try to control it through arduino really puzzles me - any help would be greatly appreciated

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You really need to post a schematic of what you think you have before we can make sensible suggestions. Are the transistors getting hot before they blow or are they just blowing cold?
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hi Mike

apologies for the crudeness of the schematic - hope it makes sense
the transistor pins are as follows:
1. emitter
2.Base
3. collector

they do not get hot - i can have the LED on for as long as I want running through the transistor but as soon as i try to control it through the arduino board they blow.
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You have no series base resistor. This will blow up the transistor because you are forcing too much current through the base. Put a 1K or so in line with the base and the Arduino's output.
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thanks for that - will give it a go.
Do you know why this problem does not occur when I use the same schematic on a breadboard? i.e. why this problem only happens when everything gets soldered in?
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It is because there is a difference in the two circuits even though you think they are the same. Make sure you have identified the emitter base and collector correctly. When you say it works without the Arduino, if that means the LED is on without connecting the base to anything then it is not wired up correctly. With the base not connected the transistor should not be on and so the LED should be off.
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To make a constant current driver high-wattage LED driver, could you use a low-power constant current driver IC like LM334 and have control the current flowing through the base of a high-wattage PNP transistor, which would in theory then drive the LED at the PNP's beta * the LM334 current?

Kind of like my 2nd diagram here http://effluviaofascatteredmind.blogspot.com/2009/02/constant-current-led-driver-thoughts.html, but replace the 2N2907 with something a lot heftier?

I'm wondering because I've got a pack of LM334s and some experience using them.  Are there advantages to buying an application-specific part?

Thanks!
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