Bike Brake Light Senses You Slowing Down


Group riding can be a bit dangerous if the pace is fast and riders don’t notice a slowing in the front of the pack. [WyoJustin] designed a brake light system for cyclists to try and remedy this issue. LEDs are mounted in the end caps of the handlebars on a road bike. When an accelerometer senses the bike slowing down the LEDs light up, warning those behind you that you’re slowing down.

The system is made to be portable, as a lot of serious riders have multiple bikes. To make this happen, all of the electronics are housed in the handlebar tubing for easy transfer. This includes an accelerometer with built in voltage regulator, an Arduino to control everything, and a battery. Take a look at the brake lights in action after the break.

Most of the bike lights we see are for the front of the machine, but this backward-facing package is a clean and easy solution we can get behind (safely).


57 thoughts on “Bike Brake Light Senses You Slowing Down

  1. @jefke
    you’re supposed to interface an accelerometer without a micro? or are you saying that a person can’t use a micro they’re familiar with?

    I think the point of using an accelerometer is that it can detect slowing down that doesn’t involve brakes, like if a person were to hit something, their light would still go on.

  2. This is a great idea, by not requiring the user to change any behaviour they are suddenly more safe than before. Plus if they are actually slowing down and they do not mean it, it is still indicated.

    Oh and to the haters, using an ATiny is cheap, almost as cheap as using a PIC and often cheaper than a PIC32.

    This design also guarantees that it’ll work on fixies (too bad) and BMXes and other kinds of bicycle braking systems.

    Also remember to use your hand signals you jerks.

  3. @nave.notnilc

    I guess he’s saying (as I would) that is overkill to use an uC for something you could do with a few simple components. Every “serious biker” has already some sort of speed meter installed. They’d be much happier if you use it somehow – grab the signal and differentiate it, who knows – instead of adding another gadget to buy and maintain.

  4. @nave.notnilc –
    No offence but surely if the person has hit something and is therefore coming to a very sudden stop you are going to be noticing the crash more than the LED showing red??
    However I get your point… Did you mean natural deceleration?

  5. Sadly, these would only mount correctly on a small number of handlebar types. Me and my bullhorn bars are SOL. Making a seat-post mounted variety would be more useful to the average commuter biker.

  6. these are much more useful for long distance group riding. I’ve been on two long distance bike trips (1500 mi and 2000 mi), and you have no idea the amount of wrecks caused by someone not paying attention and inadvertently slowing down without telling anyone. It’s become kind of standard in that group that if you ever slow down you yell it out.

    My bet is that these weren’t designed for bikes with bullhorns, they were made for long distance tours.

  7. Sadly.. The bad crossfading of the bike light video soundtrack made me flip out and stab myself.. :(

    Why go for accelerometer <-sp? Why not just use an old thermastat type mercury system.. FTW??

    Gravity on decel would cause the mercury to rush forward , completing circuit etc..

  8. very nice idea.
    i second a comment on the original post’s site: one could move this to the back of the bike, maybe even integrate it into a multi-mode blinking back light. since it has more than enough processing power already, it wouldn even need additional hardware ;)
    as several readers at the linked site pointed out: in several ways, this behaves completely different from a brake light, with a switch at the brake. i wonder how practical it is: if set too sensitively it will go on if you go uphill, set too coarsely, it will not react to slight breaking. yes, it is more portable than a switch, but a switch at the brake would signal 1/2 to 1 sec earlier than this system.

  9. @nave.notnilc, it would actually be very easy to interface an analogue accelerometer to do this without a microcontroller. op-amp differentiator, and half wave rectifier and LED driver.

  10. arduino is overkill, but for a prototype or proof of concept, i can live with that. i’d rather try something out with an arduino, than put time into developing on the final platform, only to find out, that the project is impracticable in its use.

    but that said, this comment from the author on possible improvements just gives me shivers:
    “There are plenty of pins on the MEGA, why double up on pin4 and loose independent control of the other LED? I’ve played around with this, the extra logic slows down the tracking loop.”
    just gives me shivers

    what ?? this just invites anti-arduino posts. (or more precisely, anti-arduino-users posts)

  11. Will an accelerometer actually detect that very tiny slow down when you stop peddling on a flat surface… Because if it doesnt its no more useful than a button press system linked in with the brakes (Yes i know it wont be portable but meh… simple as hell).

    Good idea though, would be cool to integrate it with other features to make a complete night-ride kit with lamps, perhaps indicators, brake lights etc…

    Practical use is limited perhaps but he enjoyed making it and he is safe at night. Who cares how useful it is.

  12. I wonder when ppl will understand that Arduino is just as good as any other evaluation platform for building prototypes. Do you seriously always use an itched or professionally made PCB for every single project?

    I agree it’s too much of it lately, but maybe it’s because there are no ‘native’ projects around?

    About this particular project, I would personally go for a RPM counter instead of the accelerometer.

  13. This is pretty neat. Simplicity for the user often trumps simplicity for the engineer. Sure you could design this more simply by tapping into the brakes or whatnot, but using a microcontroller + accelerometer means less work for the user.

  14. I like the idea of it, even if the implementation is a little overkill. I think if it was sensitive enough to detect the slightest deceleration it might make a good training tool too, a warning light whenever you are not working.

  15. @Bikr, not to mention bumps could cause the mercury to slosh around and cause some false positives.

    I imagine you could take one of those rear-red lights that many bikers have (they flash and stuff) and modify it to turn on more LEDs if you’re braking. That would keep it portable, and make it fit at the rear of the bike (underneath the seat).

  16. “This design also guarantees that it’ll work on fixies (too bad) and BMXes and other kinds of bicycle braking systems.”

    Yeah, as long as you have drops…

    I use pursuit bars and most people use regular handlebars…. making this totally worthless.

    He did a very good job on this though; if you can use it then it’s a good idea – sometimes you slow down without using breaks and it helps ALOT when group riding because one guy not slowing down with everyone else can cause a serious F up.

  17. @chris:
    you could set it up that way, just a matter of setting the threshold in the software. but it would also react in situations where you don’t want it. for example: a group goes up a steep hill, and you’re in front and pedal like crazy. while the group slows down quite a bit, you slow down only slightly, pulling away. but at the same time your brake lights go on..

    i am actually more worried about false negatives: you go down a steep hill and at some point it’s almost fast enough for you: you pull the brakes, just slightly, so you still are accelerating, but just a bit, while the group behind you is still accelerating like crazy, they just learned about your new gadget, which doesn’t work this time ..

    another problem with an accelerometer would be sensing acceleration whenever you go uphill, and deceleration whenever you go downhill. the author did some compensation for that at the end of the code, but i can’t tell of hand whether or not this would be enough.

  18. I don’t care if the hack is a working sex-bot, next time you get a demo video with such a hideous sound track just post the submitters home address so that all music lovers world wide can stop by and show their “appreciation” (preferable with a ice pick or large hammer).

  19. This would be better if it were integrated into a tail-light. Much easier to move from bike to bike, and it could be set up to be dual purpose – night time blinky safety light plus brake light. That would also save weight – which is very important for fast riders that spend $1000’s extra to remove every ounce they can from the bike.

    This instructable is one of the best I’ve seen. Great details on assembly, and even debugging hints (very rare to see those).

  20. Response to a couple of comments. This is a good concept that could use more development for sure but I think some are overthinking this.

    Example: A pack starts up a hill…there is a point where the leader starts to slow down while the rest of the group is still on level ground …could they anticipate him slowing down..sure…does this remind them to think about that? Yes it does.

    Could this be underseat mounted…or even a vest mounted unit…maybe..with some work. Maybe make the lights yellow and have them strobe faster as the deceleration increases…add switches to the brake levers (but promise not to “ride” the levers)..and have even more info for the rider behind you to process.

    The fine details of you are going downhill..pulling away…hit a bump…jiggle the brakes…have different handlebars…ride only at the back. Who cares. This is a prototype. It tries to solve a very real problem for those who ride in tight groups. It could be refined.

    Oh yeah…the simple switch idea has more problems than some of you have thought about…mercury, reed or otherwise.

    Ain’t it cool that people can get worked up about something like this though?

  21. Guys, the use of an accelerometer is not new news, you can implement a 3 axis one, and with some sine cosine rules make it account for any changes in grade, as well as any mounting differences. I’ll submit my own invention like this which I made 3 years ago for use in automobiles, to view an early promo vid, search for mitch318i on youtube

  22. Really, all these people here who ride in groups with people who can’t even use a bicycle.. find another pastime already, and who the hell enjoys cycling in a group anyway? more than 3 people is just stupid and annoying and only useful if you are an army platoon.

    As for the break handle detection, yes that’s much better if you have a bike with handoperated brakes, but not all bikes work that way.

  23. This….isn’t useful. It looks hard to install, it won’t work on all bikes(my bike doesn’t have those rear-facing handle extensions), and it blinks as you pedal. It’s not very visible, even on an overcast day like in that video. The wires would have to be exposed unless you feel like trying to thread it all inside the bars before attaching it. Not a good ‘hack’.

  24. For other kinds of handlebars couldn’t you edge-mount some rectangular LEDS or use an appropriate plastic that spreads the light?

    -or like I think I saw mentioned, an under-seat mount?

    The concept is awesome, haters sit the heck down before you embarrass yourselves further.

  25. @beverly:
    my example was: a group going up-hill, all of them slowing down, but the leader actually *less* than the rest. the bike would signal *brake* while actually pulling away from the group.
    having to break up-hill because of the person in front of you is annoying, and even more so, if it was false alarm.

    yes it’s a prototype. but part of making it into something useful is critiquing it. that’s a good thing. doesn’t mean i hate it, just means i want to think about possible improvements before i build one. i know people who rear-ended other bikers (not me), so i’am interested in it, if it works.

  26. Read the bloody article. They used arduino software and an atmega328. They didn’t use an actual arduino in the end. They used the software. You guys are such whiners. No they didn’t go and spend $40 on the arduino alone. In fact they spent #$35 ON EVERYTHING, board, chip, lights, wires.

    Read the bloody articles people.

  27. @stph no clue:

    glad you pointed that out.
    all along i thought they had bought the most expensive atmega328 arduino, and desoldered it to put the atmega328 on a breadboard.
    i am happy to learn, that it’s not an arduino but just an avr atmega328 emulating an arduino. i must have overlooked that, when i read the bloody article

  28. if he decide to use uC he could monitor speed by counting spreads with IR or magnetic sensor, it much cheaper than accelerometer , much more accurate and add ability to display speed distance what ewer, people just forget how to think

  29. @ therian Its not that people forget how to think, it’s that people just think differently. The first person who posts what they are thinking doesn’t stand a chance. Anyway; Mr. Szczys, “I” approve of this post.

  30. The idea of it is great. This belongs in cars and motorcycles too because they de-celerate on down shifts and some people in cars only watch for brakelights.

    In this day and age I would have thought a tiny micro and g sensor is the cheapest/tiniest way to do it. A chinese factory could make these for less than a buck.

  31. @Jamie: putting reliable, waterproof switches on brake levers is a job in itself, why not get hold of brake levers used on electric bikes, they have a switch built-in to tell the motor controller to cut power to the motor so it doesn’t try and ‘drive’ with the brakes on.

    I’ve often wondered about tapping into the brake sensor lines on my electric bike so I can have a working brake light that’s driven from the levers, but resisted against it so far because I don’t want to accidentally damage the motor controller during the initial investigation/testing phase (those controllers aren’t cheap).

    I really do like this approach to making a brake light, except how well does it cope when you’re going downhill at a steady speed with the brakes on? or even not using the brakes? or even uphill?

    I’ve already got an accelerometer from on the way for a different project but I might have a little play with it on my bike :)

  32. @Haku:
    uphill/downhill: the author added some code to compensate for uneven terrain and the shifting g-vector. (at least a linear approximation that works for small changes). have a look at the loop at the end of his source code.
    above i also pointed out some other problems with hills: basically, it probably doesn’t behave like people (behind you) are expecting brake lights to behave.

  33. @tantris: ahh, nice! so it’s designed to only react to sudden & long deceleration, kinda like motion sensing CCTV that only records large movements and can ignore things like the sun/shadows moving over time and analogue clock faces.

    And people say a microcontroller is overkill for this kind of thing. Shame on them.

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