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dnpurdy wrote:

In order to drive them, it looks like the best way is to use a LM317 as a current limiter, one with a 8 ohm resistor to limit to 180 mA and another setup with a 5~6 ohm resistor to limit to 250 mA. That seem about right? Under those currents, the aluminum board the stars are mounted on should be sufficient heat sink.

I think it will work if you get the 317's in the TO-220 package and heat sink them down to something. Understand that the tabs have to be isolated on them because they are not at ground potential.

I went to work thinking about new light configurations. I so want to do this. I will try to keep up with you all.

Alright, here's a quick update. I have officially started prototyping this (rather than finishing my thesis, woohoo!). So, rather than fiddle with my existing brake lights over a while and not be able to ride, I was able to find a brake light on ebay for $10. Perfect because it lets me test this in stages, make perfect fits, and have a swappable piece when done.

Upon getting the second brake light, I gutted it down to the smoky diffuser and the metal back plate. At this point I cut down a small perf board from radio shack to fit and mounted it on two risers. I think for final board I'll use 4 risers, but it is really good for finding mounting hole placement for the moment.

I put together some pictures at davidpurdy.net/BrakeLightProject.html

I'm thinking of keeping up with the photos and doing a full write up as an article on here, since some people people seem to be thinking about doing the same thing. Depending on feedback, I might give up on this.

Couple questions though. As for ordering parts, anyone know a good place to get the amber LEDs? I usually do Mouser.com, but if someone knows better, let me know. Also, should I do amber or yellow. This in the test are yellow, but super dull and narrow angle. I saw 4500 mcd/30 degree ambers and 3000 mcd/60 degree ones at superbrightleds.com. Opinions on color?

i'm almost certain this is going to REQUIRE a separate controller board for the turn signals, but that's ok. Now that I got a mockup of dimensions, I'm going to design a PCB mask that I can etch nicely to hold the LEDs w/ current resistors cleanly and that I can drop in to the existing system as "all-on" arrows until the controller board gets figured out.

I've been looking on ebay. I've seen lots of 100 or 500 in the $20 to $50 range, but i've only been looking for red ones... didn't check for yellow.

BSKZ650 wrote:

you have a cool idea,, I have seen what you are trying to do on several late model bikes, rather than reivent the wheel, adapt one of those to the bike

I had the same idea and tried for a long time to find a newer tail light that would fit correctly under my MKII tail. They also sell universal integrator boards that would work great but need to be used with clear tail light lenses - couldn't find one for my MKII. Here they are if it helps anyone:

Universal Integrator Boards

These integrator boards have yellow and red LED's and automatically convert all of your wiring to one neat integrated taillight.

Great work by the way Dnpurdy. I wish my taillight came apart like yours just leaving the clear. I think yours will come out awesome and cost alot less than you could buy one for. Keep us posted!

The project is coming along nicely. I etched a prototype board and am just waiting for the components to arrive. I was able to order 100 2000mCd Amber LEDS on ebay for cheap. Probably totally grey market, but that's what you get with cheap semiconductors, ohwell.

I do have one question I'm hoping to get some help with. So I am currently using the 1157-RLX3 bulbs from superbrightleds.com (tech specs here superbrightleds.com/specs/115x-xLX3.htm) I love them, but for space reasons, it looks like i probably will need to use the luxeons on a flat package for this taillight project.

However, I can't tell if the luxeons they are using are Luxeon I or Luxeon III. It says they have 1157-RLX3 blubs have 85 lumens at bright and 35 lumens at running brightness.

The tech specs for the Luxeon I's say 40 lumens at 350 ma, while the Luxeon III say 140 lumens at 1.4 A typical operating. I assume that means I need to buy two Luxeon III's and run them at 250ma bright/65ma dim??

Can anyone help confirm?

i hate to start up an older post but thought this would be a great addition to the topic both the website and the product. www.sparkfun.com/commerce/product_info.php?products_id=8711#

dnpurdy wrote:

The tech specs for the Luxeon I's say 40 lumens at 350 ma, while the Luxeon III say 140 lumens at 1.4 A typical operating. I assume that means I need to buy two Luxeon III's and run them at 250ma bright/65ma dim??

Can anyone help confirm?

I know with LED's, the limiting factor for current is almost always power dissipation, not the current handling capability of the LED. You need to calculate the power dissipation by multiplying the VF of the diode times the current.

I know that there are no reasonably sized LED's which could handle 1.4A continuously because that would be at least 6W of power dissipation.

The spec you need is the namufacturer's spec for the package the LED comes in: they spec what is called Theta (J-A), which is the thermal resiatance from junction to ambient. It is expressind in degrees C/Watt. Multiply times the watts dissipated and you get the rise above ambient the diode will be running. In most cases, 150C is the absolute maximum allowed for semiconductor devices.

Bear in mind, for small PC mount devices, the Theta J-A for the application will be worse (higher) when multiple devices are soldered near each other on the same board because they transfer heat to each other through the copper.

You need to get the specs for the diodes and set your upper limit on current, then selct the limiting resistor to never let it exceed that. Eyeball the light in use and see, you will likely not need to get near the max current to get a bright enough light.

IMHO, I think 250 mA would be pretty much the maximum I would use because the diode drop is typically near 4V. About one Watt is pretty the maximum a small surface mount package can handle, unless it is expressly designed to transfer heat via a metal "foot" or tab of some kind.

Alright, so my first attempt with round 5mm leds vanished with my first stolen bike, but I've re-tried with some Luxeon III's from Lumileds.

There are 9 LEDs in all 3 right arrow yellow, 3 left arrow yellow, and 3 red running/brake light ones.

Here you can see how I mounted them to a piece of .020 aluminium from home depot. I just cut and bent it into a shelf like thing real quick



Here's the suspended control electronics. It is simply 4 independent LM317 circuits feeding each line. 250 mA for the left turn, 250 mA for the right turn, 250 mA for the brake light, and 75mA for the running light.



Here's how it looks all buttoned up, turn signals removed, and red filter removed from taillight.



And with the running light going.



And turn signal



I'm thinking I might show a comparison video to the stock stuff to show the difference. the arrow shaped turn signals are AWESOME. However the running light and brake light leave a lot to be desired. It is not as wide a light, and it doesn't make the whole square "glow" red like the stock arrangment with reflecting surfaces do. I'm thinking of giong back to stock, but if anyone has ideas how to make the red wider without losing the nice arrow look, let me know!