Topic: DIY dual intensity LED tail light for 10$

[78whiteorbs]

I got a 78'cx500 cafe project on the other bikes section and
I planned on running a LED marker light and wiring it for a brake/tail light as follows:

Put an in line resister to knock down that 12v feed to like 6-8v for my running light. Then bypass the resister for the brake light circuit so I would get a burst of 12 v for the brake light . Instant dual intensity LED tail light for 10 bux instead of fifty(did I mention I was on a budget?)   I got this idea from several other forum posts but the resister to use was never specifies. I told this chick at radio shack what I needed and she gave me the part below. I put it in the circuit between the hot wire and the battery and it isn't dimming them at all. What am I doing wrong here>

the resistor is rated: 8 ohm non-inductive resistor 20 watts

I was told that if I used the smaller ones that they would burn out and not last. Anyone ever done this ? Gotta be simple electrical circuit knowledge but it is not my area .

[Steve F]

Do yourself a favor, and quit with the resistors to control LED brightness, and go to this link and build the dimmer circuit that is shown in the second drawing.  It takes a little skill and a few bucks, but you have infinite control over the "brightness".

Steve F

http://www.reuk.co.uk/LED-Dimmer-Circuit.htm

[78whiteorbs]

I decided that I will just add four more leds and wire them to the wire that makes my light tester light when I hit the brakes. So I will have  10 LEDS total when hitting the brakes but only six lit for my parking light. This seems the easiest cheapest way. Would you agree. I can solder wires to leds it's just connect the dots simple drill some small holes and secure the leds in place with high temp hot glue . I am gonna give this a try if it works  like I think it will then I will essential have a 12 dollarish dual intensity tail light. Thanks for taking the time to post that schematic though.

[mystic_1]

You'll want some current-limiting resistors in there to keep from frying the LEDs. 


Use this:  http://led.linear1.org/led.wiz


do figure what resistor(s) you need.  Treat your two groups of LEDs as separate branches (one with six LEDs, one with four) and assign appropriate resistor(s) to each.  The resistors you need shouldn't cost but a few bucks.

mystic_1

[78whiteorbs]

mystic_1 - thanks that is the kinda info I am looking for. The six LEDS are already wired see picture. I am simply gonna add the break circuit. I was thinking something had to be in there other than just led to led .
What is this though?  diode forward voltage, diode forward current (mA)? How do I get those values to plug in to that wizard. I wish I knew more about electrical circuits. I am guess it has to do with the amps that are send and the amps that are drawn or?

[mystic_1]

What is this though?  diode forward voltage, diode forward current (mA)? How do I get those values to plug in to that wizard. I wish I knew more about electrical circuits.

Those values are physical characteristics of the LED's themselves, should be printed on the packaging.

mystic_1

[78whiteorbs]

Gotcha, again thanks . I have had like twenty replies between this thread and another http://forums.sohc4.net/index.php?topic=61517.0, this one and this is the first simple answer I got , thanks

[Steve F]

I am gonna give this a try if it works  like I think it will then I will essential have a 12 dollarish dual intensity tail light.

FWIW, I bought the LED tail light that I showed in the other post (with the electronics built-in), on eBaY for around $16 +$7 S&H, and it has something like 50+ LED's.   

[78whiteorbs]

Thanks for the info, It is too big for my seat pan dimensions and the look I want. Looks always comes at a cost and are almost never convient. I looked at all the ones on the 'bay but the only ones with the dimesntions I required were like 50-60 bux.