DarthPuppy
Posts: 483
Joined: Sun Aug 11, 2013 8:45 pm
Delivery Date: 11 Aug 2013

Re: B mode brake lights

Thu Mar 16, 2017 11:53 pm

This retrofit could be a bad idea. IIRC, there was a bad accident years ago caused by a retrofit to a police vehicle designed to flash the brake lights when the emergency lights were on. The wiring wasn't done right and supposedly it impacted the operation of the brakes somehow.

golfcart
Posts: 111
Joined: Mon Jan 04, 2016 6:08 am
Delivery Date: 21 Nov 2015
Location: Virginia Beach, VA

Re: B mode brake lights

Fri Mar 17, 2017 6:46 am

I thought the whole purpose of B mode was to allow you to f*** with tailgaters... wouldn't that be ruined if your brake lights came on every time you lift the accelerator? :lol:
2015 S with Charge Package

BenTheRighteous
Posts: 62
Joined: Tue Feb 14, 2017 5:36 am
Delivery Date: 14 Feb 2017
Location: Raleigh, NC

Re: B mode brake lights

Fri Mar 17, 2017 6:59 am

gbarry42 wrote:
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.

Yeah, I suspected something similar. I have been trying to get the regen info from the bus instead and I've been pretty successful so far. I have an algorithm that works for the relatively short duration that I'm sitting in the car and testing, and it appears stable, but haven't gone for an extended trip yet.

gbarry42 wrote:
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.

If you get down and look at the area where the pedals disappear into the guts of the car, you'll see there are actually two switches that are closed when the brake pedal is in its resting state. I suspect one is a direct circuit between the 12v battery and the brake lights, while the other is an input for the CPU. I could be wrong. But if that's the case, then completing the direct circuit only could shine the brake lights without affecting cruise control.

However, if it's possible to get the lights to shine via the bus, rather than cutting into wires, I would love to try that approach first. If anyone knows the command to make that happen, please share.

DarthPuppy wrote:This retrofit could be a bad idea. IIRC, there was a bad accident years ago caused by a retrofit to a police vehicle designed to flash the brake lights when the emergency lights were on. The wiring wasn't done right and supposedly it impacted the operation of the brakes somehow.

Yes, of course safety is the primary concern here - which is why I'm trying to figure this out in the first place. Another thought I have is "what if the raspberry pi crashes at just the wrong time?" Are we left with brake lights that are stuck on? If we're wired in directly, unplugging the pi would de-energize the relay and solve the issue... but the driver has to notice the problem first. OTOH, if we turn on the lights via the bus, the only hope would be that the cpu would be smart enough to turn the lights off on its own at some point.

I acknowledge there are potential problems with any approach, including the possibility of confusing the cpu and affecting the operation of the car. Bottom line is, I'm going to keep researching, and if I feel like I'm creating a potentially bigger problem than the one I set out to solve, then that's the end of the project. But you don't know what's possible until you try.
2017 Leaf S
OpenEVSE P50-D WiFi Kit
Raleigh, NC
USA

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