newbie LED light - brakelight setup

[airbrush]

Newbie with an LED light question.
I want to make an LED brakelight for my motorbike. I know how to set up the LEDs to get the right amount for voltage through them for full brightness, but here is what I want to do and not sure if this is the right way.
Basically I want all of the LEDs to be lit up and then when you hit the brakes those LEDs will get brighter. Currently there are two power leads for your normal filament type bulb...one lights up each filament. So do I just run the LEDs at say 10ma if they are rated for 20ma. Run my power lead for those and hook up my second power lead at 10ma again to those same LEDs????

 

[jrz126]

why not just have 2 strings of leds, one lights up as the running light, then when you hit the brakes both light up?

I think you cant really notice that big of a difference between 10mA and 20mA

 

[pandaemonium]

You mean you want all the LEDs on all the time but only at full brightness when you break?

Yes, you could split the LEDs in half and get the effect, you could also use an RC (resistive-capacitive) network (all LEDs would fade in and out), and maybe a few other things, thats something to think about, might be cool! (how about pulsing in and out when breaking and releasing the break, yea!)

 

[airbrush]

yes...i want them lit up all the time not at full brightness....only full brightness when you apply the breaks...nothing fancy no fading in or out or anything.
and yes i know you can just put some more LEDs for the brake light part of it....thats not the point....I want only one set of LEDs.
How is this done?

 

[Nigel Goodwin]

As you've already suggested, you simply have two different current paths, the first low one for the light, and the second high one for the brake light. I would suggest you will need to be running the brake light current towards the maximum value of the LED's, and I suggest you decide the lower current by experimentation - just use a single LED for the experiments!. I suspect you will need more than 50% difference though, to give a similar contrast between normal lights and brake lights.

 

[fredsm]

re: LED brakelight

Should be just the ticket:

wysiwyg://43/http://www.redcircuits.com/Page85.htm

<als>

 

[airbrush]

So I should be able to adjust the brightness of the LED by the choice of resistors i use on them? is this correct? So say i'm running the first current path at half the power and the other at half again, then the LEDs would be running at full power like i suggested in my original post, no??

the other diagram that fredsm posted looks a little complicated..i'm not understanding what type of switches are used for that?? or if all of that is really necessary.

 

[Nigel Goodwin]

the other diagram that fredsm posted looks a little complicated..i'm not understanding what type of switches are used for that?? or if all of that is really necessary.

There's hardly anything in that circuit, only two transistors and one resistor more than the possible minimum. The transistors form a simple constant current source for the LED's - a better method then simple resistors.

The two switches are clearly labelled, one is the light switch, and the other the brake light switch. If your switches are in the positive, rather than the negative, you could easily make the whole circuit the other way up.

 

[airbrush]

as i said before.....total newbie here, i am trying to keep this as simple as possible.

Can anyone share an answer on what I asked? Will this work the other way with the two power leads?

 

[Juglenaut]

I was just playing around and built a LED array on a rat shack PCB.

The array can handle 800mA but it get somewhat warm, not hot.

I and using a 100ohm 3 watt resistors to limit the current at 12 volts.

These LED are 5 volt with 40mA nominal current, to work this array I series'ed 2 LEDs, then terminated one off the the positive to the middle of the series. It works and yield 1.6 volt drop and the current nominal is a little more usefull. At low power these leds show the tolerance in brightness. If the 2 series LEDS are close the voltage divide is almost equal so this current drove the middle LEDS. The only reason I put these middle LEDs in was to cover the gaps up more.

14 banks of 3 running from bus lines, total 42 and can add more.

Without resistors, this array can handle 2 amps at 6 volts before avalanching or 47.6mA each. The limiting resistor can reflect higher current than what I used, if you what it a little brighter select like a 80 ohm. I set these up to switch between one 100ohm then switch to parallel 50 ohm, low then high beam

Oh and I used no clean solder.