led taillight delima...help

Hi there,

I am making an led taillight for my motorcycle. Here is the way it is setup right now.
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what i want is the middle part to light up brighter when the brake is applied and all of it will be lit up less bright otherwise. So i wired the middle sections together as one part and the outers as another, also a few white leds at the bottom for the licences plate.
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So this is all fine and dandy...they work when i connect the positive and negative for each section individually..but when i hook them all together...ie..ground wire all together and postives together i get weird results...not working correctly.
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i have voltage regulators on each of the power leads one for normal lights and the other for brakes
can anyone tell me what i am doing wrong and how to do this properly....i'm just a newbie

If you connect them in parallel there should be no difference. Could you post a schematic of how you are wiring them?

okay i reposted an image in the original showing the wiring as it is now...you may have to clear your recent internet files goodpickles to see it...so it refreshes

if anyone could help....that would be great...i'm stumped on what i'm doing wrong

Eek!
1) Regulators in parallel without isolating resistors on their outputs.
2) Powering only 1 regulator while the other's output is still connected to it.
3) No input and output capacitors on the regulators for stability.
4) 30 and 100 LEDs wired all in parallel, or maybe paralleled 15 in series with the other paralleled 15, and paralleled 50 in series with the other paralleled 50.
5) No current limiting resistors, just letting the regulators overload and do the current-limiting.
PS, I bet they are 12V regulators with only a 12V (or 13V) input, which doesn't even matter because their output certainly isn't 12V!

Hey. LEDs are the same as ordinary 6V or 12V light bulbs, except dimmer, aren't they? :roll:

I just hope the LEDs have built-in current-limiting resistors for use with a 12V supply.

Hey Audioguru,

here is more info on it....the leds are parelled series of 5 and yes there are resistors on it...just not shown in the picture. I have no idea what you are trying to say from your comments...if you could explain that would be more helpful.

So can anyone tell me how i should set up the regulators....and how to wire up to do what i want. Can someone do up a sketch of the schematic?

Hi Airbrush,
I just said what I saw. If things were missing from your picture, my comments would be much different when they are shown.

How did you wire it without a schematic? We are fairly expert at this and we are just guessing at which you have connected to what. What about the details:
1) Voltage or part number of your regulators (we can look-up their spec's).
2) Voltage and continuous current rating or part number of your LEDs.
3) Value and power rating of the resistor for each group of 5 paralleled LEDs.
We will be able to help you only if we know those important details.

"....the leds are parelled series of 5 and yes there are resistors on it...." is very confusing. Are the 5 LEDs connected in series or in parallel, and where are the resistors connected to?

Why are you using two regulators? Since their outputs are connected together (aren't they?), they fight each other and cause weird results if only one or both are powered, especially without having an important input capacitor. A single regulator (maybe a more powerful one) and a couple of switching transistors and diodes would probably do a much better job.

are you using one resistor for each string of 5 LEDs that are in series?
what is the value of resistors? what is forward voltage of the LEDs?
what is the current? what voltage regulators you have?
why don't you simply remove them?
most voltage regulators require minimum of 2.5V input-output difference
to work correctly. If your regulators are 7812, you need at least 14.5V on the input for regulators to work correctly.
I would rather use small inverter to bust voltage and put longer LED strings. Changing brightness is best done using PWM.
Here is simple alternative circuit idea that could solve your problem.
It has variable duty cycle oscillator, selector logic and driver circuit.
Similar circuit can easily be created with other components such as 555...

Generally you would not bother with a reg. You would size your resistors for 13.8v or so, what you normally see when running with a battery.

If you expect wide variations in source voltage, put fewer LEDs in series and drop more voltage in the resistor. This makes a circuit whose current is less sensitive to source voltage variations.

Hi Panic mode,
I like it, all with only one IC.
I see that you are in "the suburb run by Hazel" too. Have you counted all those stairs at City Hall?

okay...all technical info isnt really necessary (led voltage, regulator 7810, resistors), all of that is fine. A person off of my bike forum was making LED taillights without regulators and they pulsed when idling because of fluctuations in voltage, so he added regulators to fix this, i am going by his advice of what to do. But his werent setup like i wanted...I know how to make the whole thing work if i wanted the all of the LEDs to brighten when brakes are applied, but thats not what i am after. Just the center section to light up brighter.

So what i'm starting to understand from this is that both of the outputs are hooked up to the center section that i want....which would work if the one output wasnt also powering the rest of the LEDs. So I need to isolate this somehow?

What about if I branch another power lead off of one of the existing ones and power the outer LEDS and white LEDs with that? will that work or is that still considered sharing a common output?
As I said...i am a total newbie to electronics so all help is appreciated, thx for your input, some if it is still confusing to me.

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airbrush said:

okay...all technical info isnt really necessary (led voltage, regulator 7810, resistors), all of that is fine.

Click to expand...

If you want us to help you make the brake lights turn on brighter than the normal brightness, this info is extremely necessary.

I know how to make the whole thing work if i wanted all of the LEDs to brighten when brakes are applied, but thats not what i am after. Just the center section to light up brighter.

Click to expand...

How? By adding more regulators?
If a 7810 isn't overloaded, then its output voltage will be 10 volts. The LEDs will be a certain brightness with 10 volts feeding the resistors that are in series with them. When you have a single 7810, it is probably overloaded causing a low output voltage. Your LEDs go brighter with two regulators connected because the 2nd 7810 shares the current so the 1st 7810 isn't overloaded anymore, and the voltage rises to 10 volts.
If you add 100 or more regulators all in parallel like you have both of yours, their output voltage will still be 10 volts, and the LEDs will be at the same brightness.
You need an electronic circuit to increase the brightness of the LEDs, and we can't properly design one for you without the necessary details.

So what i'm starting to understand from this is that both of the outputs are hooked up to the center section that i want....which would work if the one output wasnt also powering the rest of the LEDs. So I need to isolate this somehow?

Click to expand...

Yes, you need to isolate the center section of LEDs from the others so that you can change their brightness. You have them all connected together now.
We will help you do this when you give us the important details.

I copied a 7810 manufacturer's recommendation for capacitors and warning about connecting their outputs with only one powered:

airbrush, can you read a circuit diagram? For instance, does panic mode's circuit mean anything to you?

I can draw something which will do what you want but need to know how to present it.

okay so...the leds i have already figured out the necessary resistors etc to use on them...this is not an issue.... the leds are rated at 2.2...i am using a 3.9kohm resistor to make them dimmer and off of the brake light lead i have a 10ohm resisitor(to make them brighter). I tested this on a breadboard with a series of 5...which is what all of them are,series of 5 in parellel. And the regulators are 7810 which require a 12.5V to operate which is fine since the battery will never go below 13V.
Anyways, all of this works fine on the breadboard, so i just need to know how to isolate this correctly and run the rest of the LEDs with power as well without connecting it all together.

The guy off of my bike forum never used any capicators...just the regulator to fix the problem he had...which was the lights pulsing when the bike was idling because of fluctuation. He put the regulators in...no capcitors and that fixed it.

I'm not great with the circuit diagrams..the one posted there starts to look pretty complicated... i mean i can look up all the symbols and see what they mean etc...but its still kinda greek to me.

I appreciate everyones input, this thing is drivin me crazy :?

This will do what you want.

I m not saying that I think this is the best way to do it, but it's the way with which you are familiar and apparently comfortable.

You seem happy with your values of resistance and cpable of changing them if necessary so I didn't put in any values.

R1 sets the current through, and hence brightness, of the leds whose brightness doesn't change.

R2 sets the "dim" brightness of the leds whose brightness increases with the brakes.

R3 provides additional current to make them brighter.

The diodes isolate the regulators and the set of dim leds.

1A diodes, such as any of the 1N4000 series, will be okay.

I should have said, I realise that R1 and R2 and their associated groups of leds consist of more than one parallel paths.

okay cool....so this is basically what i have already but i need the diodes in there to keep the current from travelling back...correct? Well that seems easy enough then....

Hi David,
You have a nice, simple but very elegant solution. If the LEDs don't draw more than about 25mA each (about 2.5A total), it is perfect.

Yes airbrush, that's right. The diodes protect the regulators from current entering their output pins (from the other regulator). And the left hand one also prevents any additional current flowing through the left hand set of leds when the brakes are applied.

audioguru, you flatter me. (But I don't mind!)

And yes, but some quick mental "sums" indicate that 1A diodes will be ok.

thanks david....nice and simple everyone else seemed to want it make more complicated then it had to be... a knew someone had to know a easy solution to this. My limited knowledge of eletronics has increased more....DIODES... the all mighty saviour...haha.

I'll pick some up tomorrow and let you know how it turns out.

managed to hit the stores before they closed...picked up an assorted pack of diodes. So what do the numbers on them mean?? I have 4001,4002,4004 and 4007. I couldnt find anything on the net about the specs and what the numbers mean. Does it matter which i use?