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Design Request - Deceleration Activated Brake Lights

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by sign216, Jul 11, 2017.

  1. sign216

    sign216 Member

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    Commercial motorcycle accessories called "smart brakes" activate the brake lights whenever the vehicle starts to decelerate. This starts the brake lights a second or two faster, upon engine braking (which is strong for motorcycles) as soon as the rider rolls off the throttle. The faster brake lights are a real safety enhancement, and also allow for lighting the brake lights if the rider simply uses engine braking, without touching the regular brakes.

    Commerical devices include Gearbrake, Stoptix, VoloLights, and others, at prices of $80 to $250.

    I ask the board, can you design this for less $?

    Here's a link to one product: https://gearbrake.com/collections/s...-smart-brake-light-module?variant=15412515971

    The product's instructions are attached in a file.
     

    Attached Files:

  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Are you up to speed with Arduino?

    I'm thinking rate of engine RPM decrease, or wheel rotation rate decrease. Requires tapping into an existing sensor (tach or speedo), timing and computing a derivative. Trivial in a microcontroller.
     
  3. crutschow

    crutschow Well-Known Member Most Helpful Member

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    You could likely design one using an electronic accelerometer, such as this, with some added logic and a MOSFET.
    But it's seldom worth the effort to reinvent and build the wheel.
     
  4. dave

    Dave New Member

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  5. sign216

    sign216 Member

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    Mike,
    Engine rpm might not work, because with shifting that goes up/down independant of vehicle speed. There's a speedometer sensor cable I can tap into, but I'm leaning towards using an off the shelf accelerometer. It might be a good compromise between work and $.

    Crutschow,
    Those accelerometers you linked to are as cheap as $10 to 15. I am still learning, but you think building it myself won't end up saving any cash?

    Joe
     
    Last edited: Jul 11, 2017
  6. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    It should be easy to detect the engine rpm drop as you get off the throttle, before you shift down... Isn't that when you first want to turn on the brake light?
     
  7. sign216

    sign216 Member

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    Let me think about that. Is it right that for every significant rpm drop you also have a deleration? I think so. I'm trying to imagine it in my mind.

    Here's another thought; a mechanical switch that makes contact when the throttle is closed. It wouldn't be as complete a solution as the accelerometer or rpm decrease, but it might be super-easy.
     
  8. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    If it was a car or airplane, I would be looking at intake manifold pressure (vacuum?) . Differential pressure across the throttle plate?
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Not at all, in fact pretty well the opposite - as you're rapidly changing down the gears the engine revs will INCREASE hugely. As you accelerate and change up the gears you will get a signifiant rev DROP, and you don't want the brake light coming on when you do that. You could, of course, measure both change of speed, and change of revs, and calculate from those.

    The obvious solution though (as already suggested) would be an accelerometer.
     
  10. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    I interpret this to mean turn on the brake light as the throttle is closed, even before down-shifting...
     
  11. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Both RPM decrease and throttle closure occur during shifting and you don't want the brake light blinking for those conditions.
     
  12. sign216

    sign216 Member

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    By "decelerate" the commercial products mean a rapid physical deceleration. I.e. a quick loss of the bike's speed, not the engine speed.
    I think they must use accelerometers, because they don't have any connections to the bike's engine or speedo. Just brake light connectors.

    Would an old fashioned mercury switch do it? Or might that be harder/more expensive than the electronic accelerometer?
     
  13. crutschow

    crutschow Well-Known Member Most Helpful Member

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    The mercury tends to slosh which could cause actuation under acceleration.
     
  14. sign216

    sign216 Member

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    You're right, and I think those old switches are hard to get now (hazardous waste and stuff).

    So I'm thinking now about the electronic accelerometer. What are its parameters, and what circuit do I need?
    I'm thinking it might be simple for it to have it's own battery, to power the rear brakes when it's activated. The battery could charge off a number of bike circuits.
    For it to control the whole braking circuit might be complicated.
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I think the motorcycle is a little more complicated because of the possible lean. You need to get the forward vector. Most accelerometer go through a calibration sequence once where they are rotated (driven in a circle) and sometimes flipped to get the orientation.

    I have a compass that has a rotate slowly calibration cycle.
     
  16. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    why cant you tap into the speedo? or am i being really stupid again?
     
  17. sign216

    sign216 Member

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    Well....it's complicated. At least when the lean is great, the forward speed is usually less. Like your name, can we keep it simple, and just stick to the forward/rear dimension?
     
  18. crutschow

    crutschow Well-Known Member Most Helpful Member

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    No.
    But I don't think detecting a slowing in speed from the speedometer pulses would give as fast an indication as the TS would like.
     
  19. crutschow

    crutschow Well-Known Member Most Helpful Member

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    This accelerometer would probably do the job.
    It has a an output of 0.3V per G of acceleration, so you could use a comparator (LM339/393) with a adjustable trigger point to apply the brakes at the desired negative G's voltage.

    It requires 3.3V so you would need to add a voltage regulator, such as an LM317 for that, which can be powered from the cycle battery.
    I see no reason to add a battery.

    And the wiring shouldn't be that complicated. You just OR the signal to the brake light so either the brake pedal or the accelerometer (or both) operates the light.
     
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  20. sign216

    sign216 Member

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    Crutschow,
    Thank you for the part info. I am a babe in the woods, what does "or" mean? Should I use the accelerometer to trigger a relay, which then powers the brake light?
    I hate to ask you for much more, but can I have a rough circuit diagram, so I know what to build?
    Joe
     
  21. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    .OR.
    Depressing the brake turns on the brake lights and it's done with a switch.
    So another switch across the brake switch can also turn on the brake lights.

    .OR. One or the other or both turns on the brake lights.
    Translated: The accelerometer gizmo OR the brake switch turns on the brake lights.
     

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