[rkam]

Take a look here: http://www.kvaser.com/can/

1) Yes it is possible to send your own commands, but it will be difficult to build your own interface without using any standard chips with integrated CAN support. Many microprocessors have built in CAN support.
The bit stream of CAN-bus is more complex than RS232 and is best left to hardware to deal with.

2) If you want something sent to you, you need your own address and someone who knows you.
If you only want to send to other nodes and listen to replies to other nodes, you don't have to have your own address.

An address where more bits are set to change line voltage (1 or 0 I don't remember) will get priority on the bus.
While a node is sending the address of its target it must also monitor the line voltage.
As soon as someone else is changing the line voltage from passive to active where the low priority node would not change the line voltage, the low priority node should quit and wait a certain amount of time before it tries again.
This way the high priority nodes transmission is not interrupted.

3) The nodes should support the same physical CAN standard, but not necessarily the same protocols or command sets.

4) It should work if your stereo is connected to CAN-bus and programmed to react on commands like that.

[Mich]

Thanks for the good answers.

If I (must) build something, it will be with an AVR from Atmel with CAN support.

[jimDK]

4) Can I mute (and un-mute) the stereo with CAN-bus commands?

The volume of the radio is controllable from buttons on the steering wheel.
I would expect that these issue CAN commands to the radio (interrogate by listening on the bus while pressing them).
I believe that a software update is NOT needed, when they are added to a steering wheel, so it should work "out of the box".

[Marcel]

4) Can I mute (and un-mute) the stereo with CAN-bus commands?

The volume of the radio is controllable from buttons on the steering wheel.
I would expect that these issue CAN commands to the radio (interrogate by listening on the bus while pressing them).
I believe that a software update is NOT needed, when they are added to a steering wheel, so it should work "out of the box".

As a last resort you could indeed emulate the steering wheel buttons. But it is difficult (impossible) to restore the volume to the previous setting (unmute). Another possibility is to monitor the Volvo phone module to see how this module instructs the hu to mute/unmute. You do need access to a similar car with Volvo phone module, though.

[Marcel]

This is my first (well second) post on this forum. The text below is a copy of a post I made a few days ago on swedespeed.com.
======================
I have been working on my "VolCanExt" (VOLvo CANbus EXTender) for almost a year now. This is a link to my project topic on the Dutch Volvo forum (you need to register for this) : http://www.volvo-forum.nl/viewtopic.php?t=30184 . Currently I'm working on the implementation of a CanBus abstraction layer. This allows the VolCanExt to adapt to additional models/years more easily.

A little while ago, I was able to borrow a camera and made a few short videos: http://www.youtube.com/user/HMCSdigital

For those who are working on this: The challenge is not to get info of the bus, but to influence the car making it do what you want without storing any faults.

BTW the AEM cable in the trunk (right side) is also a good place to tap into the LowSpeed CanBus.

[rkam]

I have registered on the Dutch forum, but I could find no real information or software.

Is this something you are planning on selling when it is finished?
Is this some sort of advertising?

Also from Swedespeed:

Forum user:
Could you give us more details on solely writing info to the DIM?

Your reply:
Monitor the phone module to figure it out. It took me less than 30 minutes to figure out how to write to the BC display.

[Marcel]

It's not advertising, I just wanted to let you know what I am working on. I have not decided yet if it is going to be a commercial product. It is definitely not finished yet.

As for writing to the DIM:
I have experienced how wrong things can go when working with the canbus. Therefore I am reluctant to give out too much information. I do, however, give tips so that by thinking yourself you can figure things out.
I believe it is important to think and learn instead of being told and copy.

That's all. :)

[Tartryffel]

I could just add that the mute function isn't built-in phone-dependent, it will actually mute with a third-party phone as well, as long as it's connected to the HU unit.

[Mich]

I could just add that the mute function isn't built-in phone-dependent, it will actually mute with a third-party phone as well, as long as it's connected to the HU unit.

Could you please explain this in more detail? (kanske på svenska)

Because:
There is no connection between AUM and PHM.
There is no connection between AUM and any handsfree I know about.

AUM = Audio Module, e.g. HU-850
PHM = Phone Module, i.e. integrated mobile phone

[Tartryffel]

Det är fullt möjligt att mutesignalen går via Canbusnätet när använder den inbyggda telefonen. Men använder man en annan telefon så finns det ett uttag bak på stereon som styr ljud och mute till telefonen.

Längst ner till vänster på bilden. Bilden är på en HU-650 men det kan knappast vara annorlunda på HU-850.