TOPIC:

I had an idea today for an integrated brake light and wondering what people thought before I tried a prototype. I've been using the Luxeon 3W 1157 replacement for about a year now and absolutely love them. Having dealt with the sticky-out turn signals as a nuisance for some time, here was my idea.

Etch a flat PCB the size of the square rear tail light. Just off center, solder in two of the flat red 3W luxeon stars for the left and right running/brake lights (this would essentially just replace the two brake blubs currently installed. Just to the outside of those, put 2 arrows of high intensity yellow LED's to serve as turn signals. By taking off the red filter and leaving the clear diffuser, all the colors would show through correctly and you could have a neat integrated light with significantly lower draw on the electrical system.

The brake lights would looks exactly like luxeon 1157 is brightness on running and braking intensities. The turn signals would be directional in arrangement, with the outer strip bent slightly outside more to increase the spread of the light.

It would be a pretty easy pcb to etch and would solder up super fast. Wiring out be a simple splice in from the harness rear line.

Worth trying or totally ludicrious?

Cool idea, but you would not necessarily have to use yellow or amber for the turn indicators. Reds are legal in the back, and they are a lot brighter. I use a 3W RED luxeon tail/brake light on the center rear and two more 3W RED luxeon tail/brake lights in the rear "turn signal" light assemblies, which I converted to red lenses (not amber). Everything on the back is red on mine, the turn signals have some custom circuitry so they function both as turn and brake lights. ASFAIK, it's completely legal to have all red tunr and brakes in the rear and also legal to use the same light for turn and brake light. Cars do it all the time.

The directional arrow idea is cool.

I'm not sure how much heatsinking two 3W Luxeons would need, if they were close together would they get too hot?

In thinking about it more, I realized the heat sinking would be an issue. But I found a solution. Rather than buying new Luxeons, why not just use two 1157 sockets in the PCB board and use the functional Luxeons I already have! It would simplify the design and make construction easier. They are already have built in heatsinks and 1157 sockets are cheap. Since they are largely directional anyways, I doubt the reflectors are doing much, so those could be gotten rid of and just angle the 1157 sockets like 5-10 degrees of the front/back axis to get a slight spread.

For the details on the the directional arrow circuits, I got to thinking you could actually add the motion pretty easily. Divide the two/three/four rows of leds up and put an SCR on each line. The SCR would work that once tiggered, it would keep the "chevron" illuminated until the power was cut. If the SCR's could be progressively timed such that the innermost (#1) turned on after 100ms, (#2) at 200ms delay, (#3) at 300 ms delay, and optional #4 at 400 ms delay, you could get a really neat effect.

every time the turn signal relay turned on, you would get a motion effect on the directional arrow of LED's as it progressively illuminated the chevron.

however, I don't know how do to timed triggers for SCRs. Any EE's out there wanna help?? Lou? I think a RC circuit connected to a UJT to signal each SCR could do it.

Acutally, you could do it with only one trigger circuit serving either side. Have the trigger ciruit powered by EITHER the left or right supply, while the SCRs are tied only to their respective left/right supply. The 100ms trigger would send a signal to both the left and right #1 chevron SCR, but only the appropriate only would have a supply voltage to turn on. Additional on hazzards you'd get a nifty outwards spreading effect on both sides.

100ms seemed right, but 150ms spacing might be more appropriate.

I'm definitely going to make a prototype if anyone can supply the trigger circuitry!!

There are many ways to do this, but I think it best for you to build in stages since you are trying to incorporate several different concepts at once. For instance, the 5 yellow LEDs in series is a bit much. It doesn't leave enough voltage for the ballast resistor to work properly.

Let's assume the the SCR's are not there and we just want to turn on a stack of 5 LED's. The Yellows I deal with are 2.2volts at 25mA. 5 LED's stacked will take 11 volts. Let's assume we have a voltage range of 12.5v to 14.5v. At 14.5v, to get 25mA through 5 LEDs, the resistor has to be 140 ohms. But what happens when it's 12.5v? With 140 ohms, (and based on the I-V function of the Yellow LED's), the current will end up around 15 or 16 mA. That's a very large current drop.

To illustrate the point, let's look at two LEDs in series with a resistor. At 14.5v to get 25mA, the resistor would be 404 ohms. At 12.5v, the current drops by a lesser amount, to about 21 mA. By reducing the amount of LEDs in series, you reduce the dimming affects produced by a lower voltage.

The way around this problem would be to run everything off a small voltage regulator like a 7812 or maybe even a 7810 to make sure the voltage doesn't fluctuate. Then you can put 4 LEDs in series with a resistor. (5 would still be a stretch since the regulators need some headroom.)

As far as the sequencing goes, that can probably done many different ways. A 4-pack of flip-flops would probably do it, but there may be a ready-made IC out there that will take a clock-pulse and sequence the lights for you. But this will take some experimenting and research. You'll need to run a voltage regulator for all of this too since motorcycle voltage is very dirty and fluctuates a lot. It results in erratic timing, phantom clock pulses, and a bunch of goofy behavior.

I would recommend making the static version first with just the LED's on the display board, then make a seperate control board to run it. That way you can alter the control board but use the same display. I would split each chevron into two sets of LEDs. If you use 5, split it into 2 and 3, or if you use 7, split it into 3 and 4.

I assume you are familiar with breadboard, because that's what you should start on.

Incidently, I just started on my own brake/tail panel. It's probably gonna be awhile before it gets going. I'll probably see what cheap LEDs I can find on Ebay. They advertise some pretty bright specs. Let me know if you want to buy some since the quantities are usually in the 50 to 100 range. I'm thinking all red, but some narrow angle for brake/turn, and some wide angle for tail. That way the brake LEDs will appear brighter when viewed from directly behind.

Here is my own diode voltage-current graph. These are actual hands-on measured results, not manufacturer-advertised results.

uhhhhh....

I hate feeling clueless...

You could break up the five LED's on each arrow into two strings of 2 and 3 diodes to get better current control from the limiting resistor, and drive both sets as a single string from the top.

Instead of an SCR at the top, you could just use a PNP transistor like a 2N3906 device which can easily crank 200 - 300 mA. To get the pulse effect is easy:

use a 555 timer set up to free run at maybe 1 Hz, and use the output to drive the PNP devices to light the string. You can drive one sstring directly off the 555 output, so it lights when the output goes low. Drive the other string as follows: connect the 555 output to an NPN like a 2N3904 (emitter on ground, ) and use it's collector to light the other string. Addinf the NPN inverts so one string lights when the 555 output is high, the other when it goes low.

Yeah, that will work. I was really hoping to see if I could find a way to do cumulative lighting...so it lights up inside out and holds on until the flasher relay kills it and then cycles again when relay reconnects.

That way I was thinking it would be simpler, more rugged. If I can make it out of parts without an IC, I think that would be the most rugged

Alright, how about this.

Using the circuit I found below, I set the 555 oscillate ~13Hz. This is fed into a 4017 decade counter, where the outputs for 1,2,3 go to both the left and right SCR gates.

The SCRs are fed with direct +13.5 from the turn signal line. The 555 and 4017 are fed from a LM3085 small supply circuit.

This means first one is triggered, the next 150 ms later, the next 150 ms after that. minimal parts - with a jumper on the PCB can be set to "normal" operation if the chips fail.

Will this do it? The 5V supply circuit, 555 oscillator at ~13Hz and the 4017 decade counter on SCRs that will latch on until the relay cuts it all off??

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

So in investigating my current luxeon lights, I put a DC loop ammeter over the supply lines for my current brake lights. I have two of the 3W luxeon 1157 blubs.

On running, it showed 180 mA and at full brake it showed 220mA. Under these currents, it looks like these are technically the Luxeon I elements. Is that right? The Luxeon I's can be driven up to 750 mA and the Luxeon III's up to 1.4A.

If I wanted to use flat elements to make an integrate board and not use the current 1157 blubs I have, I would want the Luxeon I elements right?

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 would be neat if I can fabricate this as a single flat board that can be screwed onto the square brake light.