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Posted by driesdep 2 hours ago

Running Tesla Model 3's computer on my desk using parts from crashed cars(bugs.xdavidhu.me)
240 points | 69 comments
kube-system 1 hour ago|
> Turns out that actual cars don’t have individual cables. Instead they have these big “looms”, which bundle many cables from a nearby area into a single harness. This is the reason why I could not find the individual cable earlier. They simply don’t manufacture it.

I was really surprised to read this at the end of the article -- how could someone be this deep into a project of this depth and not realize this?! Not only because all cars (...er... all vehicles) are wired this way, but also because the documentation they were referencing has plenty of detail to show this... there's even a whole picture of it (and to Tesla's credit they have amazing free docs): https://service.tesla.com/docs/Model3/ServiceManual/2024/en-...

longislandguido 24 minutes ago||
Software people tend to overestimate their knowledge of other disciplines, writing it off as "easy" or work beneath them. Being overpaid compared to your peers certainly doesn't help dispel this feeling. Some people have built entire careers around designing wire looms.
entropie 51 minutes ago|||
> how could someone be this deep into a project of this depth and not realize this

I think this is a software guy who occasionally dips into hardware things (to hunt bugs).

trebligdivad 5 minutes ago|||
Yeh, it seems odd to have the cut off cables, the wiring information...and then to go and buy a loom rather than bodging a cable at that point.
kube-system 48 minutes ago|||
That's what I figure -- but it was wild to read that after reading the part about component-level PCB repair lol
spuz 41 minutes ago|||
Even if you know that cars consist of a single wiring harness, it's not implied that they aren't modular and the individual cables cannot be purchased separately.
longislandguido 13 minutes ago|||
First, cars don't consist of a single harness.

Second, why would it be implied?

Anyone with a modicum of knowledge about cars or wire looms already knows this is how it's done. So, anyone with legitimate business in the discipline.

Does everything need to be documented at a third-grade level in case some software person decides he wants to power up car parts on a table so he can write a blog post?

kube-system 37 minutes ago||||
Cars usually consist of multiple harnesses -- as it is in this case as well. The harnesses are the cables in a car. That is the part you can purchase because that is the part.

There's a list of them here: https://service.tesla.com/docs/Model3/ServiceManual/2024/en-...

MBCook 48 minutes ago|||
I will say I’m surprised how far apart the two boxes are in the car. I guess they’re not where I thought. I would assume they’re both up near the dash.
kube-system 42 minutes ago||
The passenger side kick panel or behind the glove box are two very common places for vehicle computers -- some cars have them under the hood, which I always thought was a bad idea.
msisk6 10 minutes ago||
My RAM truck with the Cummins diesel engine has the engine computer mounted on the engine block. You'd think the heat and exposure to the elements would make that a bad idea, but I suppose Cummins knows what they're doing.
FireBeyond 10 minutes ago||
> and to Tesla's credit they have amazing free docs

Not to Tesla's credit, they had to be dragged kicking and screaming into it (primarily by Massachusetts) and their right to repair legislation through a solid chunk of malicious compliance:

1. When told that they had to have a site for people to order parts, Tesla put up a site that had every single item as "Call us", including the most simple of bolts. And when a few places called, "Sorry, that's not available to you".

2. The service manual was originally only available in a few locations in MA, and had strict conditions: you had to book in advance, there was a $100 fee per booking, and you could only view the manual on premises, and could not bring electronic devices into the room with you, just pen and paper.

The docs they have are great, and who knows how their attitude would have changed over time, but they absolutely didn't want you to have it, initially.

bluGill 1 hour ago||
I used to work for a company that made third party scan tools. We had racks of ecus disconnected from the car with just a diagnostic connector and power. nothing got to a real car without first trying it on the rack. I remember on time we figured out a bmw (pre obdii) had the bytes offset from the standard documentation (it was a semi-standard protocol that some other cars used at the time), we went from we communicate but nothing is wrong to a very long list of dtcs on that controller. (All our competitors also showed nothing wrong, but the official bmw tool showed dtcs)
nandomrumber 31 minutes ago|
Diagnostic Trouble Codes?
guyzero 34 minutes ago||
Congrats, OP has recreated a test/development bench, the bane of developers working on automotive software development all around the world. They're so close to being a real vehicle that you think you'll be able to get a lot of work done, but they're not, so you don't.
sho_hn 24 minutes ago|
Honestly I love it. Few things develop a more fun camaraderie than a bringup bootcamp with two precious/priceless new samples on a large conference table, and everyone being very careful to keep cups/mugs very far away.

And a soldering robot with a specialist a few rooms away to beam down the latest errata into physical form, at times.

Tracy Kidder just died, and Soul of a New Machine was a favorite of my formative years as an engineer. Once I started in headunit ECU development it felt very familiar to me at times.

I'm a software guy, but the gear has a lot of allure.

girvo 1 hour ago||
It's funny to hear LVDS be described as an "automotive" cable when all of my run-ins with it are for connecting laptop displays to their main-boards! (though that has a very different connector on it, and its a very general term for the signalling protocol from what I remember)
slfnflctd 1 hour ago||
Not saying there's anything wrong with your perspective (lots of terms get in muddied waters, it's common and not a problem if everyone is on the same page), but this is what I just found on Wikipedia:

"Early on, the notebook computer and LCD vendors commonly used the term LVDS instead of FPD-Link when referring to their protocol, and the term LVDS has mistakenly become synonymous with Flat Panel Display Link in the video-display engineering vocabulary."

https://en.wikipedia.org/wiki/Low-voltage_differential_signa...

stephen_g 23 minutes ago|||
The cable in the article is pretty much doing the same conflation of terms that Wiki is talking about - the automotive one is a proprietary cable that carries some protocol that uses LVDS as its signalling, so at the most basic level both it and the display cable in the laptop are 'LVDS cables' but that's also the most generic term that gives you no information about the protocol actually being carried by the cables.
girvo 1 hour ago|||
Yeah I saw that too which is why I posted my comment, it's surprising to me :) LVDS for display cables was an incredibly term in that context. Even still is sometimes despite them mostly being eDP (embedded-DisplayPort) now, which is quite incorrect hah
inamberclad 1 hour ago||
SpaceWire is also just LVDS with an uber-minimal routing protocol. It runs on a lot of satellites.
a1o 37 minutes ago||
> A DC power supply capable of providing 12V

Hey, I just remembered my school used to have ages ago some cool power supplies (I think from Agilent?) that were very idiot proof, they had current limit with a dial that I think didn’t went over 1A or perhaps even less, and they would instantly disarm on short circuit (and indicate it with a led), and also the voltage dial I think wouldn’t go over 25V. I remember it was very big and heavy, but it survived countless students that used the lab daily.

Nowadays, is there any power supply available that is that resistant or is the recommended approach to get an used old one? Does anyone have a power supply at home that is also used by kids with a brand/model they would recommend? Thanks!

duskwuff 32 minutes ago||
What you're describing is a lab power supply. (The "instantly disarm on short circuit" is overcurrent protection, which is a standard feature.) The name brands like Keysight or Rigol are kind of expensive, but there are a lot of no-name models on Amazon which will do the job well enough.
bombcar 34 minutes ago|||
Those were called something like desktop power supplies.

https://www.mouser.com/c/power/power-supplies/power-supplies...

AT $5k it better make me breakfast, too.

virtue3 33 minutes ago||
They have variable dc power supplies on amazon on the cheap.

If you want that sort of reliability it will probably go towards 100$.

LikeBeans 1 hour ago||
Very cool. Over a year and a half ago I installed a towing brake controller in my Tesla Model Y. Found the location of the plug, how to access and the pinout online (confirmed via a voltmeter..) so the car's side felt straight forward. But then I needed to find a brake controller that can work with the higher voltage (14.4v vs the normal 12v). Then built a cable from the brake controller to the connector that plugs into the car that I found on eBay. I velcro'd the controller under the dashboard. It works pretty well. I towed my small camper several times with it last year with no issues. Yay! However my little project is nothing compared to this post. Love people hacking away. So cool.
ferongr 1 hour ago||
>then I needed to find a brake controller that can work with the higher voltage (14.4v vs the normal 12v)

Put a voltmeter on the battery terminals of a regular car at 2000rpm and note the voltage. You'd be surpised (the alternator can produce as high as 15V on some cars).

AlotOfReading 1 hour ago|||
Automotive transients can be wild. I did a bringup with a board that had specified 100+v range specified for transients and finicky quality requirements on the output. The power supplies took up most of the (very large) board.
mixdup 41 minutes ago||
14v is not a transient, if your voltage was 12v with the car running, there's something wrong with the charging system (DC-to-DC in an EV, alternator/generator in an ICE)

13-14v is normal in all 12v automotive systems as the charging voltage

nandomrumber 18 minutes ago||
If I recall correctly, a fully charged lead acid battery has an open circuit voltage of 13.6V.

So the alternator has to put out at least something higher than if it’s planning on recharging the battery after 500 to 700 amps have been pulled from it for a few seconds to start the engine.

nandomrumber 21 minutes ago|||
I typically fault anything above 15.6V as “that’s a bit high, your alternator might be on its way out” when working on automotive / caravan / camper van appliances and accessories.
silisili 1 hour ago||
> But then I needed to find a brake controller that can work with the higher voltage (14.4v vs the normal 12v)

Not understanding this sentence. Most running ICE vehicles product closer to that 14.4 than 12v. I think a standard controller would have worked fine?

serf 1 hour ago|||
you're correct. a '12v ICE' alternator generates up to 14.8-15.2v. Most automotive stuff can operate between 9ish-16ish-v , of course totally depending on the product.

of course this is just a modern interpretation. older stuff runs at 6v and some weirdo offbeat cars have a 24v/48v rail sitting around somewhere. Cop cars often had alternators that put out weird voltage ranges for certain equipment, or dual 12v for high amperage output.

kube-system 1 hour ago|||
Even just a "12v" automotive battery itself is mostly dead if if actually reads 12.0V. Fully charged is around 12.6 or 12.7. If a car had an electrical system that actually ran at 12 volts, the battery would always be dead.

"12v" in reference to anything automotive is very much a nominal reference.

londons_explore 1 hour ago|||
Whilst cranking, an ICE car will drop to around 6 volts (then maximum power is extracted according to thevenim's theorem).

That means all computers etc will work at 6v.

toast0 1 hour ago|||
> Whilst cranking, an ICE car will drop to around 6 volts (then maximum power is extracted according to thevenim's theorem).

> That means all computers etc will work at 6v.

Not necessarily all of them. Plenty of stuff will drop out while cranking; hopefully not the computers that run the fuel injection and ignition, though.

bluGill 1 hour ago|||
The specs say no less than 6volts. In the real world when the temperature drops down to -70F or colder and batteries get old the voltage goes well below that: deal with it.
LikeBeans 1 hour ago|||
You are probably right. Surprisingly the first controller I tried didn't work. I assumed the voltage was too high since it worked in my other (much older) car. I found a reference online of people that tried a particular brand/model and that's what I went for. Thankfully my car isn't the model with the internal 18v battery.
wodenokoto 5 minutes ago||
Say what you will about Tesla, but from a hacking point of view this is some of the coolest things I’ve seen in a while!
denysvitali 53 minutes ago||
You can run QtCar (the Qt-based app that Tesla uses for their UIs) on QEMU - if you have the firmware.

https://x.com/i/status/1722717318009041104

DM me if interested

dwa3592 17 minutes ago||
Interesting.

> A REST-like API on :8080 which returned a history of “tasks”

I am curious to know what kind of historical tasks- since it's a media control unit; does it show what kind of media was being played in the last trip? does it reveal any other info about the driver?? There might be a privacy angle here that you could exploit and share it with Tesla.

completelylegit 27 minutes ago|
People need to request the source code.. There’s a ton of open source they use that forces Tesla to give you source if you’re a customer and you ask. I don’t get why security people aren’t doing this already.
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