Arduino powered taillight project.

[robvanderveer]

The animations promise this to be an awesome product!

But I feel I must issue a word of warning. You will want your stoplights to go on AS FAST AS POSSIBLE to attract the attention of the idiots behind you. Security wise, I am very hesitant on changing anything on the car that would influence the basic functionality of the car using a mod. I don't want to be rear-ended because the Arduino driving my brake lights wasn't functioning properly. My insurance company wouldn't even think of paying up if they found out.

[john 05141]

Animated lights are not allowed in most parts in Europe.
I am certainly interested in a modern version as long as the animation can be bypassed.

I am looking foreward to see you answer Dave's Question; did you cut of the rear plastic part of the lens to install these?

Jan

[Dangermouse]

I do like the start-up animation

But I have to say that I am not a fan of the Mustangs sequential indicators. Like wheel spinners, it was cool the first few times I saw it, but it is just cheesy now. IMHO of course.

I think you should go crazy on whatever you can do for use in a car-show type setting, but be cautious about adding anything that may add to the distraction of a driver following you.

However a proportional brake light, somewhat like BMW do, would be interesting, one that perhaps lights two segments on each side, like OEM, during normal braking, but adds the third, or increases the brightness during emergency braking. Of course you would need some sort of pressure signal generator from the brake pedal.....

[jangell]

I think you should go crazy on whatever you can do for use in a car-show type setting, but be cautious about adding anything that may add to the distraction of a driver following you.

I've been toying with doing something similar -- I got so far as building my LED order, but got sidetracked by some other stuff. It's cool to see this project (and I'm also curious about if the lens housing thing was cut off to install them).

I am quite concerned about safety, so most of the things I was going to do were very quick animations. It was more of a learning exercise and because it would look kinda neat, and would be fairly subtle. Animation is good at drawing your eye if it's done correctly, too. I've often wondered if the slight fade up/down of incandescents is better than the popping on and off of LEDs in braking and turn signal applications for that reason, but I'm not really sure.

My plan was to preserve the original DMC taillight region purposes. So, my turn signal might quickly animate only the yellow bit from the center of the car towards the edge, then stay illuminated for the rest of the "blink" before the "off" animation runs. For the brake lights, they might start from the center of the light and very quickly animate out to the edges. If you brake hard, I'd also light up the tail light, and maybe have it flash or something like some high-end cars do (which I see is what you also suggested below).

However a proportional brake light, somewhat like BMW do, would be interesting, one that perhaps lights two segments on each side, like OEM, during normal braking, but adds the third, or increases the brightness during emergency braking. Of course you would need some sort of pressure signal generator from the brake pedal.....

Disclaimer: I have no real knowledge of car lighting safety engineering; I just think about these kinds of things more than I should:

Increasing brightness is tricky -- the problem is that you need something to compare it to, which is particularly tough to do in different lighting conditions. Also, if you look down the highway at night you'll notice that all car taillights are almost exactly the same brightness as all other cars, and all brake lights are all brighter than taillights by the same amount. I once saw someone who had put brake bulbs in their tail lights and it was really distracting because it looked like they were braking all the time.

So the first trick is getting your LED intensity to match the stock setup so that you don't confuse everyone else on the road. After that, it seems like either changing the intensity of, say, the edges of the of the lights or blinking all or part of the light is probably safer than adjusting the brightness depending on how hard you press the pedal.

As for detecting how hard you're pressing on the brake pedal, I think one or two more switches at different positions along the brake pedal's travel would give you the information you need to start flashing the lights. This assumes that "pressing really hard" means that the brake pedal is moving down further than "pressing kinda hard", which I'm pretty sure it is, since the brakes wouldn't work otherwise.

Even without the LEDs, I think you could probably rig up a "flash the center tail light" with an extra switch on the pedal and a simple circuit on the tail light wire. Seems like it could be an interesting project for someone, although since you're starting to delve into car safety I'm not sure anyone could sell it (I have no idea how that stuff works) -- it might be restricted to a DIY project.

-- Joe

[Dangermouse]

Also, if you look down the highway at night you'll notice that all car taillights are almost exactly the same brightness as all other cars, and all brake lights are all brighter than taillights by the same amount.

While this used to be true, apparently with the advent of LED tail-lights, the DOT appear to have thrown that particular section of their code out the window.

Look at the LED brake lights on a big Infiniti SUV - they are blinding, but possibly because they are at eye-height.

I suspect the code says something about limiting a tail light to 25W, and a brake light to 55W, which is irrelevant with an LED, and the code just hasn't caught up.

[jangell]

Back when I was playing around with this I googled for information on the lumens of a taillight bulbs, which seemed to be a good way to figure out how bright the LEDs need to be. Of course I don't remember what that was anymore. I figured I could divide the number of lumens by the number of LEDs, but I'm not sure it's a linear relationship (it probably isn't). Mostly I was going to buy LEDs that were too bright, then PWM them down to match incandescents.

I didn't know that some LED-based taillights in production cars are much brighter than conventional taillights. That's sort of annoying, actually, but at least it gives us some room for mods.

-- Joe

[Tomcio]

I don't know exactly what the DOT says but I got some EU specifications for the exterior lighting and was very surprised to see how they describe the rear light intensity. For the front they have exact numbers for lumens for the headlights and turn signals. The turns signals have different minimum values based on the distance from the headlight. Pretty complicated matter...
For the rear it's a completely different story. While the color of the light is given exactly as 610nm and up for the RED the brightness is more of a "looks good enough" kind of deal. The official specification says that the rear light has to be red and has to be visible at a distance of 400 meters in clear weather at night (it doesn't state by whom). The brake light needs to be distinctively brighter. There is a rule that say that the brake light should be 60 - 185 candela for EU and 80 - 300 for the US. Generally the LED tail lights use full brightness (constant supply at max LED current) for brake lights and 30% PWM for taillight operation.
As for the "panic brake" function do not even consider using switches on the brake pedal. This will not work! The pedal travel differs based on temperature, moisture in the fluid and other factors. This can be done in two ways:
1. Use a pressure sensor in the hydraulic system - complex, expensive and generally not a very good idea.
2. Use an accelerometer chip connected to the Arduino. Then write a code that reads the deceleration and activates "panic" function when a certain value is reached. This is fairly easy to do and would work great. Just make sure to interconnect both taillights so this function activates both lights at the same time.
There is a regulation in Europe for those "panic" brake lights and it reads:
UN Regulation 48 calls for the lamps providing the ESS (Emergency Stop Signal) to flash at 4 Hz when a passenger car decelerates at greater than 6 m/s2.

As for animations... very illegal in Europe. General European rules do not allow any kind of animation for the brake lights and to be honest I want all my brake lights to activate at the same time. People follow DeLoreans way to close and I want to give them a clear signal that it's time to hit the brakes as soon as possible. Animated brake lights might send a mixed message... what's that? That's cool what his lights are doing... wait, is he slowing down? Oh crap... CRASH! Turn signals... maybe, but brake lights are a big no-no for me.

[jangell]

That's great information about the light intensity, wavelength and panic light blink speed -- thanks! Weird that they aren't very specific about the rear light intensity, though. I should really hunt down the DOT specs sometime...

I definitely agree that brake lights need to be immediately recognizable (really, any indicator lights). I'm probably not clear about what I mean by "animation" for my project, but if I'm not confident that it would be safe I won't do it.

I also didn't think about brake pressure vs. pedal travel vs temperature/moisture being an issue for detecting panic stops. My thought was more that if you were panic-braking, you probably had your foot on the floor, at which point the specific pressure wasn't very important. I was wary of using an accelerometer because it was a secondary input (the behavior of the car braking) instead of a primary (telling the car to brake), but perhaps I'm overly concerned about that. Your mention of the 6 m/s^2 spec suggests that I am that an accelerometer is a way to go. Also, it would ensure the lights flash only when you're actually panic-stopping, and not just sitting at a stop light with the brake pedal down hard.

I likely would not want to rig up a pressure sensor -- as you said, that's probably pretty complex, and I'm not sure I want to inject new hardware into the system required to make my car stop.

-- Joe

[bttws]

So many responses... Thanks everyone. Once I get home and back to a keyboard make a longer post. I answer a quick question... Yes. I did cut the lenses off. (And it not come off without a fight.) I'll post some pictures when I get home.

[bttws]

Also my design does have a option for panic stops. I'll post about that too.