BenTheRighteous
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B mode brake lights

Wed Mar 08, 2017 1:05 pm

So as I'm sure we're all aware, B mode can slow down the Leaf significantly without touching the brake pedal. However, your brake lights don't come on in such circumstances.

I've searched and found lots of discussion about whether the lights should come on, but nothing as far as someone having actually done something about it.

Let's say I was interested in making sure my brake lights were on anytime I have >2 bubbles of regen active. What's the best way to go about that?

I see two options:
Hardware mod: maybe find the wire that controls the 3rd regen bubble in the dash, and splice it out to a relay that is hooked into the brake lights.
Or...
Software mod: build some kind of device that that plugs into the OBDII port, which monitors the regen level and sends a "brake lights on" message.

Any thoughts on which is more feasible, or if there are other options I haven't considered?
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chirpyboy
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Re: B mode brake lights

Fri Mar 10, 2017 11:12 am

Interesting idea. I believe the brake lights are purely controlled by the switch at the brake pedal, so you couldn't light them up through the port or can bus.

Getting into the main meter to tap the regenerative brake status light sounds tricky, maybe it is easy but I bet you'd have to crack it open and find a specific trace on a circuit board. The best way is probably reading the regen status from the OBDII port (like LeafSpy can do).

Perhaps you simply rig something up with a standalone accelerometer instead of trying to read the regen signal.

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Re: B mode brake lights

Fri Mar 10, 2017 12:42 pm

Touch the brake pedal.

But if you do come up with an electronic approach I think it would be a good idea as I have the same concern when in traffic.

BenTheRighteous wrote:Let's say I was interested in making sure my brake lights were on anytime I have >2 bubbles of regen active. What's the best way to go about that?
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IssacZachary
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Re: B mode brake lights

Fri Mar 10, 2017 2:00 pm

BenTheRighteous wrote:So as I'm sure we're all aware, B mode can slow down the Leaf significantly without touching the brake pedal. However, your brake lights don't come on in such circumstances.

And as mentioned before, the same is true of stick shift cars that the driver has the habit of engine braking. Engine braking can also considerably slow down an ICE car and it does not turn on the brake lights in any way.

Yodrak wrote:Touch the brake pedal.

But if you do come up with an electronic approach I think it would be a good idea as I have the same concern when in traffic.

BenTheRighteous wrote:Let's say I was interested in making sure my brake lights were on anytime I have >2 bubbles of regen active. What's the best way to go about that?


I agree. We all have brake pedals. If you "touch" it the brake lights come on. You can tap it and literally flash your brake lights on and off. We also have flashers.

An electronic device would be nice too. Not necessary, but nice, as long as it were well designed.

To me, I think if someone made an automatic brake light device the brake lights should turn on dependent on speed change, not level of regen. If I'm going down a hill with the car in B mode I don't need the brake lights on down the whole hill. No other car turns on its brake lights just because the person has downshifted and is engine braking.

Either that or braking force, or both. Maybe regen can turn on only certain brake lights, or on for 3 seconds, off for 3 seconds. Then the brake pedal can turn on more brake lights, or keep them on or make some flash quickly. But again, there are times that brake lights left on, like going down a hill, aren't necessary.

This kind of reminds me of driving comercial vehicles. Big comercial vehicles many times have a braking device called a retarder. There are several kinds of retarders, and some turn on the brake lights when activated, and others do not. With some retarders it is possible to just leave the retarder set as you come down a long mountain pass, as long as it doesn't turn on your brake lights. That way, when I hit my brakes because I really need to slow down the cars behind me see my brake lights come on and realize that I'm slowing down now. But with the kind of retarder that turns on the brake lights we generally use those intermittently. Basically I speed up about 5mph, put the retarder on and slow down 5mph, speed up 5mph and then retard back 5mph. That way if I suddenly need to slow down the brake lights stay on, signaling that I'm now actually slowing down considerably.
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BenTheRighteous
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Re: B mode brake lights

Mon Mar 13, 2017 8:21 am

chirpyboy wrote:I believe the brake lights are purely controlled by the switch at the brake pedal, so you couldn't light them up through the port or can bus.

Getting into the main meter to tap the regenerative brake status light sounds tricky, maybe it is easy but I bet you'd have to crack it open and find a specific trace on a circuit board. The best way is probably reading the regen status from the OBDII port (like LeafSpy can do).

I came to the same conclusion this weekend. I'm going to try to make a Raspberry Pi talk to the OBDII port and then physically wire it into the brake pedal position switch.

The hardest part (at least for me) will be making the Pi talk to the OBDII port. I made some initial progress but I'd love feedback. I started a separate thread for that here: viewtopic.php?f=44&t=23639


Isaac - My first step is going to be to get something - anything - working and then write up a walkthrough online that others can follow if they wish and modify as they see fit. In my area, there are no long downhill / mountain slopes to be concerned with, and seeing brake lights down a small hill is common. Unfortunately, people getting rear-ended at intersections due to inattentive drivers is also common. So that's why I'm going to get the simplest (and most important) use case working first, and if others would like to tweak it even further to add conditionally flashing lights or other features, I would absolutely encourage them to do so!
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jpadc
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Re: B mode brake lights

Mon Mar 13, 2017 1:32 pm

BenTheRighteous wrote: Unfortunately, people getting rear-ended at intersections due to inattentive drivers is also common. So that's why I'm going to get the simplest (and most important) use case working first, and if others would like to tweak it even further to add conditionally flashing lights or other features, I would absolutely encourage them to do so!


You should probably check the CFR 571.108 - Standard No. 108; Lamps, reflective devices, and associated equipment carefully before recommending modifications to how automotive brake lights work. My quick check of it does suggest that the wiring of the brake lights which MUST come on "upon application of the service brakes" seems to also include language that suggests they MAY be set up to come on "by a device designed to retard the motion of the vehicle" which I guess arguably might include regenerative activity in b mode without pressure on the brake peddle. I say arguably here because the increase in regenerative energy in b mode is not a device "designed" to slow the vehicle, that's just a side effect of reclaiming more of the vehicles kinetic energy back to the battery so I'm not offering a legal opinion about whether such a modification would qualify under the language of the code.

But the code is pretty definitive on brake lights being "Steady burning." Not that you can't find plenty of items on eBay (like this one) that make brake lights flash. However, I don't think I'd be recommending people add such devices and I note, coincidentally I'm sure, that most all of those sellers are from outside the US and therefore, as they say in the biz, "judgment proof." But unlike window tint laws that are state dependent and pretty inconsistent, federal brake light standards are not things I'd want to modify on my vehicle and have to explain after an accident with an argument of "well I thought it was consistent with the code and I thought it would improve safety."

Just a random thought... Carry on.
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BenTheRighteous
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Re: B mode brake lights

Mon Mar 13, 2017 5:43 pm

Ah, thanks for the reality check.

My encouragement earlier was actually just for people to contribute to the mod in general, not specifically for the flashing lights feature.

My dirty little secret is that, at least with the way I'm going to wire the circuit, interrupting the brake lights with a flash the way most people would want would not be possible.

But I appreciate the concern and the feedback nonetheless!
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redLEAF
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Re: B mode brake lights

Tue Mar 14, 2017 4:32 am

BenTheRighteous wrote:So as I'm sure we're all aware, B mode can slow down the Leaf significantly without touching the brake pedal. However, your brake lights don't come on in such circumstances.

I've searched and found lots of discussion about whether the lights should come on, but nothing as far as someone having actually done something about it.

Let's say I was interested in making sure my brake lights were on anytime I have >2 bubbles of regen active. What's the best way to go about that?

I see two options:
Hardware mod: maybe find the wire that controls the 3rd regen bubble in the dash, and splice it out to a relay that is hooked into the brake lights.
Or...
Software mod: build some kind of device that that plugs into the OBDII port, which monitors the regen level and sends a "brake lights on" message.

Any thoughts on which is more feasible, or if there are other options I haven't considered?


Or simply buy an EV that does this automatically (VW e-Golf, any Tesla and the BMW i3 come to mind); they do this by turning them on once the car's deceleration rate reaches a certain point and at least on my e-Golf seem to work pretty effectively to warn those behind you that you're slowing down a bit faster than simply taking your foot off the accelerator; I've also owned a few stick shift cars and while down shifting will slow you down its not at the same rate that most EV B mode works that have them. Tesla will also show via a small car icon on the display cluster in front of the steering wheel when the brake lights are being turned on -- nice added touch. As their new Model 3 (at least at this point) won't have a similar unit, hopefully maybe a heads up display will do the same thing --- need to wait and see. Just like a 3rd brake light, I see this as an added safety feature that should be incorporated in EV's to keep others from following too close and reduce rear end collisions.
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Re: B mode brake lights

Tue Mar 14, 2017 9:00 pm

Maybe something like this would be easier to integrate.
http://www.digikey.com/product-detail/en/adafruit-industries-llc/1018/1528-1011-ND/4990760
Similar chips are in many phones.
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Re: B mode brake lights

Thu Mar 16, 2017 11:19 pm

BenTheRighteous wrote:maybe find the wire that controls the 3rd regen bubble in the dash

This almost never works with dense, highly optimized (for production and cost) electronics. The signal you seek is probably multiplexed with all the other segments. The IC controlling it is not in a package, but under an epoxy blob. The driver transistor die for the display segment might be right on the glass behind the indicator. So, you'll almost certainly need to use plan B.

chirpyboy wrote:I believe the brake lights are purely controlled by the switch at the brake pedal, so you couldn't light them up through the port or can bus.

Not really. The modern computer way is to sense the pedal switch as "an input". The lights are considered "an output". The firmware then gets a rule saying, "When the brake switch is detected, send a message to light the lights." That means our CANBUS gadget can turn on the lights with a message. It can also sense the brake switch without splicing into it. It's also such that you may find a message telling the regen bubbles to light up, or you may be able to light them yourself. I remember a stunt from years ago where someone had the dash displaying an absurd range number.

BenTheRighteous wrote:I'm going to try to make a Raspberry Pi talk to the OBDII port and then physically wire it into the brake pedal position switch.

All well and good, but keep in mind that the switch has other uses. If you use cruise control to maintain downhill speed, closing that switch will disengage it.
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