LED Basics

[Blurred Talon]

Many people will notice I've got a hard on for LEDs and I'm not talking about the plug and play ones either.

The LEDs I use are what are called a Superflux style of LED and looks like this:

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The LEDs I prefer to use are made by some of the following companies:
Phillips Lumiled - Philips Lumileds LED Lighting | LUXEON LEDs | LED Lighting Solutions
Cree - CREE | LEDs for the LED Lighting Revolution
Nichia - Nichia Corporation
Marktech (Cree reseller) - LEDs, Photo Sensors, Custom LED Assemblies | Marktech Optoelectronics

Other cheaper versions (4 chip, Piranha, etc) can be found from the following companies:
Oznium - LEDs - underbody kits, cathodes, flexible LED strips, dome lights
Best Hong Kong - Besthongkong - Eastern LED Source Shop: Loose LED, High Power LED, Car Auto LED, LED Light Bulbs, LED Strips, LED Flashlight, LED Module - Besthongkong - Eastern LED Source Shop: Loose LED, High Power LED, Car Auto LED, LED Light Bulbs, LED Strips, L
eBay - I'm sure you know the URL for eBay.

I do recommend the brand name ones, they are usually pretty cheap (.25 cents to a $1 per but you usually have to buy a minimum of 1 tube or 60 LEDs). Another good thing about the brand name LEDs is you can get them all bin matched meaning they are all the same color and voltage tolerances.

Now working with these LEDs is fairly simple. All you need to make a board is drill board/perf board (BHK sells it cheap), something to make a template, some resistors, a soldering iron/solder and some patience. This info is intended for people who want to use these LEDs for things like Dome Lights, Trunk lights, etc. For things that are constantly on like DRLs, Turns/Markers, Gauge lights, etc you will need a voltage regulator and PWM, I will post more info on this later.

How do you know the resistor that you need to use? Simple.
Let's say you've got Lumiled Superflux Part number HPWT-DH00 (note these are Red Orange LEDs but the idea is the same for all colors).

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Written on your tubes are 2 numbers you need to look up in the data sheet provided on the Lumiled website (SuperFlux LEDs | Philips Lumileds Lighting Company). These numbers are G32 on the tubes pictured, these are the bin codes I was talking about. G is your Luminous Flux, 3 is your Dominant Wave Length and 2 is your voltage forward bin.

The most important info is the voltage forward rating, in this case it is 2.31Vf @ 70mA, you will always be given a mA rating that this test was run at. Now you can run it at lower mA and it will extend the life of the LED and make it a bit dimmer. If you run a higher mA it will be brighter but not last as long.

So now we know that the Vf is 2.31V @ 70ma. How do we find out the resistor valve?
Meet the LED Series Parallel array wizard - LED series parallel array wizard

You will need to fill in your source voltage (14.5V for most car applications), your Vf (2.31 in this case), your mA (70mA) and the number of LEDs in your array (I'd suggest 3 at least). You can have the wizard tell you the color codes too. Now hit design my array and it will pop up a little diagram and tell you the resistor value, 120ohm in this case.

I'll post some more later on tonight!

 

[ramsack]

I used to be crazy about LEDs. It pisses me off that they call these new TVs LED-TVs, even though they are just backlit by LED. I would like to know why the world is shifting away from semiconductor LEDs in favor of OLEDs. The OLEDs don't last as long, aren't as bright, and are just retarded. I could give 2 shits if a TV is thin as paper and can be wrapped to any shape.

 

[GRAVEDIGGER]

Very interesting and informative. Thanks for the info and I look forward to hearing more.

 

[Blurred Talon]

Thanks guys!

Now, let's talk about soldering LEDs.
First off I would recommend you have some experience soldering before tackling an LED project. LEDs do not like heat and it is possible to burn one out if you suck at soldering or have a shitty soldering iron (like I do).

Buy yourself a quality soldering station, there's many good brands out there like Weller.

You will also need good quality solder, I use a .035 lead solder, I don't believe in led free personally.

Next you need some copper back (or clad) perf board, Best Hong Kong sells it for the cheapest I've found yet.

How do you solder your LEDs and resistors to perf board you ask? Check out this link: Physical Computing at ITP | Tutorials / Soldering A Perf Board

With just these things you can easily make your own LED boards for various car lighting projects.
Here's my Dome light:

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Here's my turn signals (chrome vinyl was applied to hide the circuit board through the clear lens):

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My advice when doing your own LED is go slow and have lots of patience. When I first did my turn signals it took me about 3 hours to solder all the connections, 4 legs per LED times 30 LEDs is 120 connections. You will make mistakes so have some spare LEDs on hand.

Later I will post some information on PWMs and Voltage regulation.

 

[GRAVEDIGGER]

I again find it very informative and interesting and will look forward to hearing more about voltage regulation and pulse width modulation with the LEDs. LEDs are so cool. I think I could get carried away with putting them everywhere.

 

[ramsack]

I see the need for a voltage regulator on something like a car where the voltage can fluctuate, but you don't need PWM in a circuit unless you want to control brightness. Even that's not needed to dim them. I suggest using a 5v regulator and then a current-limiting resistor from there. That way you don't need to worry about the voltage ranging from ~12-~14v.

 

[BoSsRsT]

Thank You Blurred! I needed a thread like this! I just ordered a set of headlights and wanted to do the same thing you did with the indicators. Im pretty good at soldering, but never actually tried to solder LEDs. I'm definitely gonna subscribe to this thread.
Thanks for all those links too..

Sent from my SAMSUNG-SGH-I897

 

[ramsack]

I'd like to convert all exterior light bulbs (except the headlights and fogs) to LED in a fashion you retrofit stuff. I just hate messing with taking apart lens assemblies.

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I made this circuit about 10 years ago. Anyone guess what it does?

 

[Blurred Talon]

I again find it very informative and interesting and will look forward to hearing more about voltage regulation and pulse width modulation with the LEDs. LEDs are so cool. I think I could get carried away with putting them everywhere.

I can guarantee you will get carried away.
By spring all the exterior lights on my car will me LED (with the exception of my DRLs).

I see the need for a voltage regulator on something like a car where the voltage can fluctuate, but you don't need PWM in a circuit unless you want to control brightness. Even that's not needed to dim them. I suggest using a 5v regulator and then a current-limiting resistor from there. That way you don't need to worry about the voltage ranging from ~12-~14v.

For interior lights or dedicated turn signals I wouldn't bother with a PWM, it's pointless.
I usually voltage regulate to 12V in all my projects because it's what I prefer, you can do 9 volts or 5 volts but stepping 12-14V down to 5V will require some heat sinks because it's such a big difference. This is why I prefer the 12V regulators (I usually use Sharp LDO regs).
Now with my dome and trunk light I only used resistors because they dome light is not on for very long at all so I didn't want to go through the hassle of setting up a Vreg. However if someone wants they can certainly run one.

Thank You Blurred! I needed a thread like this! I just ordered a set of headlights and wanted to do the same thing you did with the indicators. Im pretty good at soldering, but never actually tried to solder LEDs. I'm definitely gonna subscribe to this thread.
Thanks for all those links too..

Sent from my SAMSUNG-SGH-I897

Thanks, I've got more links coming in a bit.
Just remember take your time.

 

[ramsack]

I don't see why a PWM circuit is needed for anything other than dimming, so what's the point in either interior or exterior? Regulators usually require a couple volts above the output voltage as an input, that's why a 12v regulator is pointless. It won't raise voltage for you. A heat sink doesn't need to be huge, nor does a person need to get a puny voltage regulator compared to current draw on the designated circuit. 9v would be the wiser choice. For a car to see 9v would mean other things wouldn't even be running. I doubt the battery can even support much current if it was that drained. Not trying to start a war, just a healthy discussion.

 

[knochgoon24]

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I made this circuit about 10 years ago. Anyone guess what it does?

I'm guessing that it blinks the lights in a row. Plans for a turn signal?

 

[ramsack]

It can do that, yes. So 99% correct. It is set up go back and forth like KITT's lights. They are very bright. I once hooked it up to my HDD indicator on my computer and it was pretty sweet looking with different HDD activity. All it would take to go one direction would be a disconnection of one pin. In the picture it's also missing the 555 timer IC.

 

[knochgoon24]

In the picture it's also missing the 555 timer IC.

I was going to say that but didn't know if you had run something else.

It's been a while since I've done stuff with LEDs. Back in high school I wired up some silly LED lighting under my dash and seats. I went cheap on the LEDs and they were several different colors varying from a light blue to violet purple. Should have all been blue. Don't go super cheap on LEDs.

 

[ramsack]

There used to be a great supplier on ebay of LEDs based in Hong Kong. They were affordable and from what I could tell very good quality. I ordered 100 white LEDs and was planning to light a garage with them. I was always amazed with RGB LEDs and there was a circuit like 15 years ago in a magazine that used a PIC controller to change the colors. This was before semiconductors were small enough to have logic on the same LED die to switch colors.

 

[Blurred Talon]

I don't see why a PWM circuit is needed for anything other than dimming, so what's the point in either interior or exterior? Regulators usually require a couple volts above the output voltage as an input, that's why a 12v regulator is pointless. It won't raise voltage for you. A heat sink doesn't need to be huge, nor does a person need to get a puny voltage regulator compared to current draw on the designated circuit. 9v would be the wiser choice. For a car to see 9v would mean other things wouldn't even be running. I doubt the battery can even support much current if it was that drained. Not trying to start a war, just a healthy discussion.

As I said it's really up to what the person wants to run, most people use 12V Vregs when doing LED work in a car from all the stuff I've read over the years. azdave builds PWMs with 12V regulation built in (9V is available on request though).
Since the PWMs I plan to use have Vregs built in, I plan to stick with the more common 12V versions.

PWM are good when you have all 3 functions combined in your tails like 2G Eclipses do, marker/turn/brake. You need the marker to be dimmer then the other, that's why a PWM is used usually. Of course remember that the PWM isn't actually dimming the LED either but that's another post for tomorrow.

 

[ramsack]

A PWM circuit is going to take up too much space IMO for just dimming a light that's supposed to be dual filament. It's as simple as having 2 resistors, 1 for full brightness, and another for partial brightness. Nothing else is needed. Much simpler than a PWM circuit. I can tell even the auto manufacturers use a PWM for the same purpose for some stupid reason. I can tell by turning my eyes really quickly and I can see the stepped or strobed trails of lights.

A PWM is actually dimming the LED. To our eyes, and electrically. LEDs dim by limiting current. Current holds time in its domain, so pulsing something really does limit the current. It's kind of a duality.

A 12v regulator is going to require 14-15 volts minimum to regulate to 12. Sure you can design around that and have an resistor be less value, but the LEDs will dim then. Then are way more sensitive than incandescents in dimming with small voltage drops when they are all in parallel.

 

[Blurred Talon]

A PWM board is no bigger then a deck of cards, plus if you know where to go they are very cheap and set up for being in a car.

Again, there's a 100 ways to do this and I'm simply sharing the way I do it.

 

[ramsack]

And so am I. A resistor is the size of a resistor and costs only a few dollars. I'm adding to it to try to simplify stuff for people in complexity and cost.

 

[Blurred Talon]

How will the LED then now the difference between a marker input and a brake input?

I've tried hooking an LED to two input (marker and turn) and it would only work on marker.

 

[ramsack]

A dual filament bulb has two inputs and a ground, so an LED circuit an have 2 inputs and a ground, or two grounds and a positive, depending on how the car is wired. No need to add diodes on the inputs to prevent voltage from leaking back as what is controlling them are just simple switches.

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The only pain in the ass is that you have to find the resistor value for dim to match whatever LEDs you choose. Once you know the value for x number of LEDs you have the value needed to dim one, and can use that math with later applications with the same LED. It will require a wirewound resistor of around 50 watts for 50 LEDs because of all the current, and they are kind of pricey and don't offer a huge variety of resistance values. What kind of resistors are you using BTW?

 

[Blurred Talon]

I usually use regular carbon film resistors of varying wattage depending on the application.

Here's a couple really good links.
Notes on LEDs - Notes on LEDs
Don's LED Page - Don's LED Main Page
Pulse Width Modulation Explained - Pulse Width Modulator PWM visual helper
High Brightness LEDs and Thermal Management - Intro to High Brightness LEDs, Driving + Thermal Management

 

[ramsack]

How don't the resistors burn out? You're passing almost 4 amps through a tiny resistor at 12 volts and 50x 70 mA LEDs. Way past a 0.25, 0.5, or 1 watt rating... Interesting one of those links. I've never heard of white LEDs using color temperature to describe them. I've always seen U and V chromatic coordinates.

Oops, a 10 watt wirewound resistor would be sufficient for 50x 70mA LEDs. There are plenty of close-enough resistance options for 10 watt wirewounds than 50-watters. I still don't see any good info about PWM and how to make circuits for them. I will post something of my own rendition on that later, then.

 

[Blurred Talon]

I'm running my arrays in series parallel, I'll use my front turns/markers as an example.
30 Cree P4 Amber LEDs at 2.5vf @ 70mA. There's 3 LEDs per series with a 68ohm 1W resister that the end of the series and 10 series in total. The whole thing only uses 700mA from the source.

To be honest I'm buying my PWMs from some HIDP members instead of making my own, it just makes it a bit easier for me.

 

[BoSsRsT]

Thanks guys!

Now, let's talk about soldering LEDs.
First off I would recommend you have some experience soldering before tackling an LED project. LEDs do not like heat and it is possible to burn one out if you suck at soldering or have a shitty soldering iron (like I do).

Buy yourself a quality soldering station, there's many good brands out there like Weller.

You will also need good quality solder, I use a .035 lead solder, I don't believe in led free personally.

Next you need some copper back (or clad) perf board, Best Hong Kong sells it for the cheapest I've found yet.

How do you solder your LEDs and resistors to perf board you ask? Check out this link: Physical Computing at ITP | Tutorials / Soldering A Perf Board

With just these things you can easily make your own LED boards for various car lighting projects.
Here's my Dome light:

You must be logged in to view this image or video.

Here's my turn signals (chrome vinyl was applied to hide the circuit board through the clear lens):

You must be logged in to view this image or video.

My advice when doing your own LED is go slow and have lots of patience. When I first did my turn signals it took me about 3 hours to solder all the connections, 4 legs per LED times 30 LEDs is 120 connections. You will make mistakes so have some spare LEDs on hand.

Later I will post some information on PWMs and Voltage regulation.

Blurred can you take a pic of the back of that perfboard that you soldered for the blinkers? And how did you wire it up from there?



Sent from my SAMSUNG-SGH-I897

 

[ramsack]

So...700 mA at 2.5 volts is still 1.75 watts. Almost twice a 1 watt rating. The only thing saving the resistor could be PWM...so you are cutting corner after corner and spending more (or charging) to achieve it. Isn't 2.5 volts a little low, too, for those LEDs? I was looking at the Marktech P4 LEDs, concave, and the max voltage is 3.0 volts. Just giving them 2.5 is a serious loss in brightness without extending life. I would run 2.95 to them. PWM will save them a little bit. Without PWM I would run 2.8 volts to them. They probably aren't even seeing 2.5 volts because you are using a 12v regulator along with a PWM and other nonsense.

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For anyone interested that is a PWM circuit, probably the cheapest way to make one. PWM circuits are mainly useful in controlling brightness in things that will blend oscillations together, for instance filamented light bulbs or motors. A wirewound potentiometer is the only mechanical device that will dim a light bulb. They get hot and wear out if constantly adjusted, so a PWM circuit is the most useful way to control a light bulb. The filament stays lit after it's shut off so you don't see the pulses like you do with an LED. A PWM circuit is never going to get something to full voltage or none at all since there is always a duty cycle.

Time output (pin 3) is high = 0.693 (R1 + R2) C1
Time output (pin 3) is low = 0.693 (R2) C1

Frequency (Hz) = 1.44 / ((R1+ 2xR2) C1)

Q1 is a PNP transistor, so the LED is going to turn on when pin 3 goes low, so R2 would be the best to be a potentiometer and not R1. For pulsing a negative voltage instead of a positive, use a NPN transistor and focus on R1's value. All values to calculate will be absolute, for instance a 4.7 µF capacitor would be 0.0000047 F.