13 ms·

> But yeah, because headlights and blinkers needllessly complicated, cough er, need data uplinks.... totally NOT to check with Toyota if you've subscribed to th

> But yeah, because headlights and blinkers needllessly complicated, cough er, need data uplinks.... totally NOT to check with Toyota if you've subscribed to their monthly "safety package" for $7.99, That’s not what’s happening. The value in a CAN bus control is that you can significantly reduce the wiring requirements. Old school blinkers and headlights would require separate power wires for every function: Blinker, low beams, high beams. Those separate wires would each be snaked through long wiring harnesses back to relays somewhere else in a central location. With CAN, you can run a single large gauge power and ground pair and use the CAN bus to tell the remote module what to do with tiny signal wires. It may not sound like a big deal, but cars have a lot of electronic pieces all over. Simplifying wiring can add up to a significant weight and cost reduction. You now also have the ability to add more monitoring, such as simple sensors to detect when a bulb has failed Vehicle manufacturing is ruthlessly optimized. Vehicle manufacturers wouldn’t add complexity to common systems if it didn’t pay off.

exabrial 4y ago
that part was a joke, fyi. CAN is very useful, but tends to be overused as well: https://www.caranddriver.com/news/a41611379/gmc-hummer-ev-taillights-expensive/ https://www.caranddriver.com/news/a41611379/gmc-hummer-ev-ta...
londons_explore 4y ago
And yet the obvious thing is for someone to be making and selling a "can bulb" - a tiny 4 pin bulb with 12V, GND, CAN-H/L pins. And all bulbs (led or not) on a car would be that. It would turn on/off commanded by the canbus and report status info back. Yet car manufacturers don't do this. CAN transceivers are still too expensive to build into every bulb. Instead, a single CAN transceiver and microcontroller will control a whole set of nearby bulbs (eg. brake, indicator, reversing lights). That then makes it vehicle specific, so you don't get the economies of scale of just making a single model of can-bulb which fits lots of places in many cars from many manufacturers.
- robryk 4y ago
  How would the bulb know which one it is?
  - the__alchemist 4y ago
    ID field.
    - doublesocket 4y ago
      It's more like a class field. All bulbs of class "brake" turn themselves on for a brake message etc.
      - the__alchemist 4y ago
        Gotcha. Embedded in the frame?
        sgtnoodle 4y ago
        CAN frames only have space for 8 bytes of payload, unless you upgrade to CAN-FD at a significant complexity cost. For the sake of a light bulb, you could make it work by being sufficiently clever. You could even use all 8 bytes for serial number, and then use existence of the message itself to turn on the bulb. Have it turn off after 100ms of timeout. It's really not a sustainable approach to try to address nodes on a CAN bus by serial number, though. CAN is content addressed rather than receiver addressed. Due to the way arbitration works on the bus, it's invalid for two nodes to transmit to the same CAN identifier. The arbitration mechanism breaks down and results in error frames, at which point the CAN bus is in a degraded state. That would preclude a CAN enabled bulb from being able to send telemetry back, at least until the bulb was provisioned an identifier. That could be done by an ECU sending a frame with the bulb's serial number and assigned identifier. You still need a zero-conf discovery protocol, though, and so you're back to transmitting before provisioning. You could work around all that, but it's a lot of work. Stepping back a bit, running a car's CAN bus over a light bulb socket is going to cause some practical reliability problems. Compared to a wire harness going into an ECU, a user serviceable bulb socket is going to be much more prone to intermittent connections from vibration, as well as oxidation and wear. Intermittent connections on CAN_H/CAN_L tend to cause a ton of frame errors, and significantly degrade the overall bus performance often to the point of system failure. When a node encounters enough error frames, it is compelled by the standard to go into a BUS-OFF state where it isolates itself from the bus. Because it's a bus and all the nodes share the same two wires, it's pretty much impossible to diagnose where an intermittent connection is without trial and error.
rpcope1 4y ago
> Vehicle manufacturing is ruthlessly optimized. Vehicle manufacturers wouldn’t add complexity to common systems if it didn’t pay off. You make it sound as though this intended to be a benefit to the consumer or the end product. Having worked on and around cars, and being friends with people who do for a living, I am really unconvinced that the manufacturers do a lot of this for any consumer-friendly reason, rather than simply trying to squeeze a buck out of you. I can absolutely tell you that Volvo, for example, does what the GP is talking about, and then some. On an old school GM or Toyota, if you break a simple switch or knob, or things that really should just be simple devices, you can just pull it out, go to the junkyard or a parts retailer, and put the new one in and be on your way. Not so for Volvo (and I'm sure this has caught on in other manufacturers): if your switch or control or whatever fails, and its hooked up to the CAN-bus, whatever replacement you find simply won't work until you've gone to the dealership (if they even let you use a part that didn't come from there at all) and gotten them to flash the part and whatever other crap needs flashing like a BCM to get them to be compatible (I think just flashing the serial number of a BCM or whatever it needs to play nice with to the switch), at the tune of a couple hundred or more dollars each time. So in essence, a stupid simple part, that should have been $5-10 that the manufacturer likely never would have seen a dollar from in the aftermarket, is now a $200+ dollar flash at the dealership, using the manufacturer scan tool, and also increasingly requires only parts the manufacturer can generate. So no, I really am extremely skeptical, given what occurs *today* that 95+% of the junk on CAN bus is there for any reason other than to boost dealership and manufacturer profits for no other reason than the fact they can.
- mayormcmatt 4y ago
  I never got the impression the previous poster was saying this is a benefit for consumers; he's saying it's for the manufacturer, to cut costs. Edit: that being said, all your points are completely valid.
  - spookthesunset 4y ago
    It is a benefit for consumers. Lower weight for better fuel. More fancy gizmos on the car for a lower price.
deleted 4y ago
[deleted]
outworlder 4y ago
> The value in a CAN bus control is that you can significantly reduce the wiring requirements. I'm adding a CAN bus to my 3d printer for this exact reason.
JohnFen 4y ago
> Vehicle manufacturers wouldn’t add complexity to common systems if it didn’t pay off. I know this stuff "pays off" for the manufacturers, but I really wish they'd avoid including unnecessary complexity such as those horrific touch screens, call connections, etc. That sort of thing is why I won't buy newer cars.
bambax 4y ago
> Simplifying wiring can add up to a significant weight and cost reduction Maybe, but given the explosion of weight and cost of new vehicles, it's unclear where these savings went.
m463 4y ago
> ruthlessly optimized One huge problem is that they put the smart key on the same bus as other stuff (headlights, body control) to save money/wiring. These kinds of busses should be buried far inside the dashboard or some other hard-to-reach area.
Schroedingersat 4y ago
So give the essential stuff its own circuit. Or encrypt and mandate the owner gets to set the key.
batushka3 4y ago
Mate have you seen old relay controled car? It has 3 times less wires and is repairable with simple tools. "Simplifying wiring can add up to a significant weight and cost reduction" it's just not there.
Tangurena2 4y ago
I used to work for General Motors. Many of the early luxury cars would have 100+ wirings going into the driver's door. Early versions of what has since evolved into CAN were trying to reduce it to 5 wires.
- jacobgorm 4y ago
  I owned a Peugeot 306 (not a fancy car by any means) that developed a short somewhere in the driver's door complex pre-CAN wiring harness. Getting it replaced cost me around $500.

exabrial 4y ago

that part was a joke, fyi. CAN is very useful, but tends to be overused as well: https://www.caranddriver.com/news/a41611379/gmc-hummer-ev-taillights-expensive/ https://www.caranddriver.com/news/a41611379/gmc-hummer-ev-ta...

londons_explore 4y ago

And yet the obvious thing is for someone to be making and selling a "can bulb" - a tiny 4 pin bulb with 12V, GND, CAN-H/L pins. And all bulbs (led or not) on a car would be that. It would turn on/off commanded by the canbus and report status info back. Yet car manufacturers don't do this. CAN transceivers are still too expensive to build into every bulb. Instead, a single CAN transceiver and microcontroller will control a whole set of nearby bulbs (eg. brake, indicator, reversing lights). That then makes it vehicle specific, so you don't get the economies of scale of just making a single model of can-bulb which fits lots of places in many cars from many manufacturers.

robryk 4y ago
How would the bulb know which one it is?
- the__alchemist 4y ago
  ID field.
  - doublesocket 4y ago
    It's more like a class field. All bulbs of class "brake" turn themselves on for a brake message etc.
    - the__alchemist 4y ago
      Gotcha. Embedded in the frame?
      - sgtnoodle 4y ago
        CAN frames only have space for 8 bytes of payload, unless you upgrade to CAN-FD at a significant complexity cost. For the sake of a light bulb, you could make it work by being sufficiently clever. You could even use all 8 bytes for serial number, and then use existence of the message itself to turn on the bulb. Have it turn off after 100ms of timeout. It's really not a sustainable approach to try to address nodes on a CAN bus by serial number, though. CAN is content addressed rather than receiver addressed. Due to the way arbitration works on the bus, it's invalid for two nodes to transmit to the same CAN identifier. The arbitration mechanism breaks down and results in error frames, at which point the CAN bus is in a degraded state. That would preclude a CAN enabled bulb from being able to send telemetry back, at least until the bulb was provisioned an identifier. That could be done by an ECU sending a frame with the bulb's serial number and assigned identifier. You still need a zero-conf discovery protocol, though, and so you're back to transmitting before provisioning. You could work around all that, but it's a lot of work. Stepping back a bit, running a car's CAN bus over a light bulb socket is going to cause some practical reliability problems. Compared to a wire harness going into an ECU, a user serviceable bulb socket is going to be much more prone to intermittent connections from vibration, as well as oxidation and wear. Intermittent connections on CAN_H/CAN_L tend to cause a ton of frame errors, and significantly degrade the overall bus performance often to the point of system failure. When a node encounters enough error frames, it is compelled by the standard to go into a BUS-OFF state where it isolates itself from the bus. Because it's a bus and all the nodes share the same two wires, it's pretty much impossible to diagnose where an intermittent connection is without trial and error.

rpcope1 4y ago

> Vehicle manufacturing is ruthlessly optimized. Vehicle manufacturers wouldn’t add complexity to common systems if it didn’t pay off. You make it sound as though this intended to be a benefit to the consumer or the end product. Having worked on and around cars, and being friends with people who do for a living, I am really unconvinced that the manufacturers do a lot of this for any consumer-friendly reason, rather than simply trying to squeeze a buck out of you. I can absolutely tell you that Volvo, for example, does what the GP is talking about, and then some. On an old school GM or Toyota, if you break a simple switch or knob, or things that really should just be simple devices, you can just pull it out, go to the junkyard or a parts retailer, and put the new one in and be on your way. Not so for Volvo (and I'm sure this has caught on in other manufacturers): if your switch or control or whatever fails, and its hooked up to the CAN-bus, whatever replacement you find simply won't work until you've gone to the dealership (if they even let you use a part that didn't come from there at all) and gotten them to flash the part and whatever other crap needs flashing like a BCM to get them to be compatible (I think just flashing the serial number of a BCM or whatever it needs to play nice with to the switch), at the tune of a couple hundred or more dollars each time. So in essence, a stupid simple part, that should have been $5-10 that the manufacturer likely never would have seen a dollar from in the aftermarket, is now a $200+ dollar flash at the dealership, using the manufacturer scan tool, and also increasingly requires only parts the manufacturer can generate. So no, I really am extremely skeptical, given what occurs *today* that 95+% of the junk on CAN bus is there for any reason other than to boost dealership and manufacturer profits for no other reason than the fact they can.

mayormcmatt 4y ago
I never got the impression the previous poster was saying this is a benefit for consumers; he's saying it's for the manufacturer, to cut costs. Edit: that being said, all your points are completely valid.
- spookthesunset 4y ago
  It is a benefit for consumers. Lower weight for better fuel. More fancy gizmos on the car for a lower price.

deleted 4y ago

[deleted]

outworlder 4y ago

> The value in a CAN bus control is that you can significantly reduce the wiring requirements. I'm adding a CAN bus to my 3d printer for this exact reason.

JohnFen 4y ago

> Vehicle manufacturers wouldn’t add complexity to common systems if it didn’t pay off. I know this stuff "pays off" for the manufacturers, but I really wish they'd avoid including unnecessary complexity such as those horrific touch screens, call connections, etc. That sort of thing is why I won't buy newer cars.

bambax 4y ago

> Simplifying wiring can add up to a significant weight and cost reduction Maybe, but given the explosion of weight and cost of new vehicles, it's unclear where these savings went.

m463 4y ago

> ruthlessly optimized One huge problem is that they put the smart key on the same bus as other stuff (headlights, body control) to save money/wiring. These kinds of busses should be buried far inside the dashboard or some other hard-to-reach area.

Schroedingersat 4y ago

So give the essential stuff its own circuit. Or encrypt and mandate the owner gets to set the key.

batushka3 4y ago

Mate have you seen old relay controled car? It has 3 times less wires and is repairable with simple tools. "Simplifying wiring can add up to a significant weight and cost reduction" it's just not there.

Tangurena2 4y ago

I used to work for General Motors. Many of the early luxury cars would have 100+ wirings going into the driver's door. Early versions of what has since evolved into CAN were trying to reduce it to 5 wires.

jacobgorm 4y ago
I owned a Peugeot 306 (not a fancy car by any means) that developed a short somewhere in the driver's door complex pre-CAN wiring harness. Getting it replaced cost me around $500.