slate blue

Can any body explain the differences in how for e.g the wheel sensors work in a CB system? Or any other example would be good. Thanks Greg

Ducman82

a can-bus system is basically a net work style system. one pair of wires can run multiple sensors.

Giovanni

Control Area Network: http://en.wikipedia.org/wiki/Controller_area_network

DR

Being a redneck I have heard of a $hit wagon, but never heard of a can bus before..

OH, you mean those fancy Controller Area Network protocol type things. Cool stuff!

I have had enough experiance with those to know to be VERY carefull with wiring/shielding as they can be sensitive in that way.

Try here, Google is your friend... http://www.google.com/search?q=CAN-BUS

Silver79

The way that I always understood CAN BUS to work is that you are able to send more information with less wiring. Usually you have two wires carrying signals to control modules. They are twisted together to cut down on interference and run in parallel to control modules. These wires are called a twisted pair. Lets say you have a four door car. Each door has a door control module that is responsible for cotrolling window operation and door lock operation. Each door control module reports back to 1 main module, lets call it a comfort module. When you send the signal to lower the passenger rear window from the driver's door window switch it goes to the comfort module which then sends the signal to all of the door control modules. The code that is sent is only correct for lowering the passenger rear window, all of the other door control modules ignore the signal. The passenger rear window is then lowered. Hope this helps.

GlenL

I've done some work with CAN bus. It's another protocol for communication. There's no specific physical layer, but it has to have certain properties for bus arbitration. Anyways...

It lets many "peer" processors hang on a signal wire and all communicate in one-to-one or one-to-many ways. This lets each initiate a message, like "Car in drive," and each can then do a local action like lock doors and turn on lights.

ptuomov

Is the CAN bus fast enough to control things like traction control? I seem to recall when looking at the service manuals of my Infiniti that all low-latency systems seemed to have dedicated communication paths. No need to parse the message addresses etc. Maybe I misremember and/or misunderstood it.

slate blue

Thanks silver79 that is the type of info I was after, I did search but could not understand it. I suppose I understand a bit of can bus 101 but not how it actually sends that data. E.g it doesn't seem to use analogue voltage signals but packet data. Are the sensors still analogue? Or something else? Also compatibility and diagnosing what is in various factory systems such as a language if there such a thing? Greg

Silver79

It's been a while since I've looked at the signals on a scope but I believe the waves are square, meaning digital. I am a Volkswagen tech and we don't really run into that many problems with CAN BUS and the things that we do see are usually broken wires or bad control modules. It sometimes gets interesting when you have a control module fail and you are not able to get coding out of it. A lot of the newer cars modules have long coding and vary with what options are on the vehicle. You sometimes have something like 8 letters or numbers on one line of code and you have like 16 lines of code. Weird things can happen if you screw up the code too such as back up lights staying on all the time, rear hatches that work with the outside trunk release, but not with the release button in the door, or windows going up when you are pushing on the button for them to go down to name just a few. There can be nothing wrong with a car besides the coding in a control module causing strange behaviors. Joe

dr bob

Think along the lines of an automotive version of "token ring" networking, and you should be close.

neilh

Great Dr B, not many will ever know what a token ring is or was!- only us old mainframe network guys :-)
My Range Rover uses a variant of the CAN -BUS, actually a single high band width single fiber-optic in a mux/demux config from front of car to back with a backup fail safe, - fortunately not made by Lucas, it's Bosch, so hopefully its more reliable.

Now, back to our regularly scheduled thread ......

slate blue

Joe that is the info I am after, just say you want to fit a late model ABS system, you will most likely need can bus. Also the electronic throttle will be tied in somehow. So is the Can Bus code more like a line of program in a computer than a voltage or pulse signal coming from say a wheel sensor. Is this topic so complex that you really need an IT background to understand what is happening? If so what type of person (qualification) is an expert in this field?

Thanks Greg

RKD in OKC

Isn't the Can Bus slang for that truck that comes around on trash pickup day for the recyclables?

GlenL

CAN bus is a digital communication protocol. It's like Ethernet in that the packets are transmitted over all kinds of physical layers (fiber, twisted pair, wireless).

You need to get a software engineer who works in embedded systems to write custom programs for you. You also might need an electrical engineer to bridge the physical differences. Maybe there's off-the-shelf hardware. Typically CAN runs on very small processors to be cheap. It's a specialized skill set. It's not an "IT" technology.

At commercial rates a project like this might run $20k or more.

There are a number of standards that build on CAN to make interoperability easier. For example, if oyur car and the brake controller are both CANOpen compliant the work will be easier.

blown 87

Try to fix a VW that some one has put a aftermarket radio in, you will learn more than you ever wanted to about Can Data.

The cars got so complex that the manufactures had to do something to limit the size of the wiring bundles.