# Design Request - Deceleration Activated Brake Lights

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#### sign216

##### Member
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 $? Here's a link to one product: https://gearbrake.com/collections/s...-smart-brake-light-module?variant=15412515971 The product's instructions are attached in a file. #### Attachments • 579 KB Views: 95 #### MikeMl ##### Well-Known Member Most Helpful Member Are you up to speed with Arduino? I'm thinking rate of engine RPM decrease, or wheel rotation rate decrease. Requires tapping into an existing sensor (tach or speedo), timing and computing a derivative. Trivial in a microcontroller. #### crutschow ##### Well-Known Member Most Helpful Member You could likely design one using an electronic accelerometer, such as this, with some added logic and a MOSFET. But it's seldom worth the effort to reinvent and build the wheel. #### sign216 ##### Member Mike, Engine rpm might not work, because with shifting that goes up/down independant of vehicle speed. There's a speedometer sensor cable I can tap into, but I'm leaning towards using an off the shelf accelerometer. It might be a good compromise between work and$.

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

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#### MikeMl

##### Well-Known Member
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?

#### sign216

##### Member
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?
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.

#### MikeMl

##### Well-Known Member
If it was a car or airplane, I would be looking at intake manifold pressure (vacuum?) . Differential pressure across the throttle plate?

#### Nigel Goodwin

##### Super Moderator
Is it right that for every significant rpm drop you also have a deceleration?
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.

#### MikeMl

##### Well-Known Member
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...
I interpret this to mean turn on the brake light as the throttle is closed, even before down-shifting...

#### crutschow

##### Well-Known Member
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.
Both RPM decrease and throttle closure occur during shifting and you don't want the brake light blinking for those conditions.

#### sign216

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

#### crutschow

##### Well-Known Member
Would an old fashioned mercury switch do it?
The mercury tends to slosh which could cause actuation under acceleration.

#### sign216

##### Member
The mercury tends to slosh which could cause actuation under acceleration.
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.

#### KeepItSimpleStupid

##### Well-Known Member
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.

#### large_ghostman

##### Well-Known Member
why cant you tap into the speedo? or am i being really stupid again?

#### sign216

##### Member
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.
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?

#### crutschow

##### Well-Known Member
why cant you tap into the speedo? or am i being really stupid again?
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.

#### crutschow

##### Well-Known Member
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.
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.

#### sign216

##### Member
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

#### KeepItSimpleStupid

##### Well-Known Member
.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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