[Ovmsdev] CAN bus noise?

Mark Webb-Johnson mark at webb-johnson.net
Mon Sep 23 17:04:45 HKT 2013


If you run in listen-only mode (CAN_WRITE=0), there is very little impact on the car. In my experience, in that mode the only thing that would worry me would be a cabling fault (short, loose connection, etc).

In active-mode (CAN_WRITE=1), the MCP2551 chip actively participates on the bus, so the chances of problem are much greater (in particular if we are also actually transmitting messages on the bus).

In theory, if the CAN bus timing is off, then problems can also occur (especially in active-mode).

The chipset we use (PIC + MCP2551) has highly tested in automotive environments.

Regards, Mark.

P.S. Every time I've been called in to look at a CAN bus error with OVMS, it has been faulty cabling. Thankfully, since we switched to factory-assembled cables, I haven't seen this.

On 23 Sep, 2013, at 4:12 PM, Matt Beard <matt at beard.tv> wrote:

> I am concerned that the OVMS v2 may be adding noise to the CAN bus, or causing problems in some other way (I know very little of CAN hardware, so can't really speculate much).
> I have heard other people mention CAN errors when OVMS is connected and yesterday I made my first trip with the unit connected to my C-Zero. During this trip the traction control failed - something it has never done before. The problem went away when the car was turned off and on again, but it seems too much of a coincidence for this to be unrelated.
> Does anyone have any opinions on this?
> Matt Beard
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