regarding the led in tail lights

i am starting a retro fitting of led tail lights for my car

need to ask one question ..

How to make the led's dual way ( i mean when the parking is on it will glow dim and as soon as brake is hit it glows on full brightness)

like the same in this pic




I would be thnakful to you for helping me out

Wire the top array as parking lights and the bottom array as brake lights.

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Let's Go Brandon Brown. Congratulations on your first Xfinity Series Win. LGBFJB

thank you but i am not interested in those ,i need the same led to be dim and bright when brake pedal is hit

there's a system for the same which i want to know

How many LEDs are you going to be using?  How are you currently planning on hooking them all up?

LEDs brightness are usually controlled in one of two ways - current limiting or pulse width modulation (PWM).

An ideal setup would run at 5vdc as to not be effected by battery fluctuations and would use PWM to control the intensity based on the parking light and brake light signals.  You can do it with current limiting but it will take some trial and error to get everything working perfect.  The "best" way to use current limiting would be to spec out a resistor for parking lights and a smaller resistor for brake lights.  Then, set the brake light signal up to interupt the parking light when it is active (so you don't have the added current of the parking lights going to the LEDs). 

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Kevin Pierson

will use approxinmately 40 led (RED) in one light ,havent decided the design will try for the passat style type

dont you thin 5vdc is too low
we found the resistor which hellps decreasing the current flow to the led's (put three ) the dimmer got to 60% of the full

it was working perfectly on the inverter but as soon as i put it on car socket it does not work at all

kindly shed some light on pulse width modulator and how it works and how the wiring would be ?

No, 5vdc isn't too low at all, most LEDs are rated from 2 - 3.6vdc.  You just need to make sure your current and voltage supplies are designed correctly to achive optimal performance.

PWM involves sending pulsed voltage to the LEDs instead of contant voltage.  I recently did an LED dimming project that used a 1Khz pulse width.  The pulse is a square wave and can be adjusted from 0% (all off) to 100% (all on).  The cool thing about PWM is you set the system to work at full brightness and your intensity is then linear throughout the pulse width % (as opposed to the non linear results you will get from adjusting current). 

PWM will require a processor (or a controller) to use so it is a bit more involved.

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Kevin Pierson

Use 15 for parking and 25 for brake lights.

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Let's Go Brandon Brown. Congratulations on your first Xfinity Series Win. LGBFJB

You should also research the legal requirements (DOT standards) for brake lights.  I believe there are requirements for exactly how bright the brake lights need to be.  The last thing you want is to modify your brake lights and then cause an accident and have a lawsuit on your hands.  You may even need DOT approval to run custom brake lights on the street, but I'm not sure about that.

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Kevin Pierson

@k Pierson: thanks for the info

for the DOT approved thing it's not issue here in india

can you provide me PWM details and links for the same and wiring details

Do a google search for PWM you'll find lots of stuff.

All the PWM stuff I have done I have used a microcontroller.  Most microcontrollers will have the PWM hardware/software already integrated in to them so it is only a few lines of code and some interupts to make it work.

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Kevin Pierson

If you just want to do it the easy way(and cheaper way) do the current limiting resistors. What I need to give you the values you should use is: Forward voltage, max continuous current, and how many leds in each series. I just was working on a taillight conversion for my Jeep Wrangler. Though KPierson is right, you will have to play with the resistor values alot to get what you want. But a stupid easy way to do it is test it with potentiometers(1k should do). Here is a circuit for 15 red leds in 3 sets of 5 with 2 volt drop and configured for 20ma at full brightness and about 5ma at dim.



Here is a look at one of the lights

Since your in India these regulations don't apply to you but may to others reading the forums, besides it took me awhile to find this.
DOT Federal Light regulations Part 571 Just scroll down to Figure 1 as it will give candela min/max values.

For figuring out how many LED's to use in series and parallel use this led calculator and for figuring the resistance total of resistors in parallel or in series use the12volt calculator here.

Be careful wiring a bunch of LEDs in series - if one goes bad you'll lose the entire strip of them, and then you'll increase the current to the remaining LEDs (since you are only using one resistor) which will most likely burn out the rest of them quickly.

If you are going to have paralleled groups at least use seperate resistors to insure that the current can't change if an LED does go bad.  If I were doing taillights or brake lights (or anything else that could have an impact on my personal safety) I wouldn't even think twice about using a dedicated resistor per LED just to make sure an individual LED failure wouldn't lead to a catostrophic situation.

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Kevin Pierson

So you want me to use 30 resistors and 45 diodes....

Yep, that's how I would do it if I were going to use a current limiting approach to control them.  It is a bit excessive, but you won't have to worry about over currenting EVERY LED if one LED were to fail (and with that many LEDs chances are one will fail within 5 years if not sooner).

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Kevin Pierson

Well figured I won't need 45 diodes but just 17. Thought custom things were suppose to be cheaper

Well I still think that would be excessive. I can just wire each set individually.

zybeon wrote:

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...Thought custom things were suppose to be cheaper

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Heh... figure out how much and how long it'll take to do something. Then, multiply each number by at least 4 to get actual time/cost.

BTDT

Jim

Also just realized that my first circuit had the wrong resistor values. Wired for each led to get about 6.5mA instead of 20mA, though not nearly as bright as I wanted it, if one went dead knocking out a set the others would get brighter but still be far within comfortable operating ranges. For the first one to work at a good brightness I would need to change the 120 to about 50 and the 1k to a 500.

Thats better, at least you are protecting the other groups if one group fails.

Diodes are cheap - you can get 100 of them for $13.  If your component prices are too high, you are buying them from the wrong place.

To "make" something like this should cost about $25 (+ shipping) with most of the expense being in the two circuit boards.  The LEDs, diodes, and resistors wouldn't be much at all.

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Kevin Pierson

thanks all guys for helping me out

i have found the system for the led's ,i think it's the same as the zybeon posted
found the diode and the dimmer resistor in local market done the trial and errors 4 times and got it perfect in 5 th time

Will post the details later