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AUTOMOTIVE CAN BUS

 
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championx



Joined: 28 Feb 2006
Posts: 151

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AUTOMOTIVE CAN BUS
PostPosted: Tue Dec 28, 2010 2:00 pm     Reply with quote
Hi! before I say anything, sorry for my english!

Well, I'm making an automotive CAN BUS data logger, I have two boards that can "talk" to each other on can bus at 250 kbps and 500 kbps.

The question is, if I connect one of these boards to the CAN BUS port of a car, I should be able to "look" at the information present on the bus, like RPM, SPEED, etc??

I also have to do this on a truck... I think that the protocol is j1939 right?

thanks!
ezflyr



Joined: 25 Oct 2010
Posts: 1019
Location: Tewksbury, MA

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PostPosted: Tue Dec 28, 2010 2:17 pm     Reply with quote
Hi,

Coincidentally, I saw a similar project today for the Arduino. There seems to be a lot of information there about the CAN bus interface, and reading the data you mention.

http://code.google.com/p/opengauge/wiki/OBDuino

Good luck!

John
collink



Joined: 08 Jan 2010
Posts: 137
Location: Michigan

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Re: AUTOMOTIVE CAN BUS
PostPosted: Wed Dec 29, 2010 6:29 am     Reply with quote
championx wrote:

The question is, if I connect one of these boards to the CAN BUS port of a car, I should be able to "look" at the information present on the bus, like RPM, SPEED, etc??


Not exactly... the OBDuino project shows this. Basically you have to ask for the info you want to receive through the use of PID codes. If you hook your device up and send the PID code in the proper format then you should get a reply back with the info you requested.

This link to wikipedia has a lot of helpful info that will get you started:
http://en.wikipedia.org/wiki/OBD-II_PIDs

Quote:

I also have to do this on a truck... I think that the protocol is j1939 right?
thanks!


Yeah, that's a popular protocol on trucks (and, to some extent, on electric vehicles too.)
championx



Joined: 28 Feb 2006
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PostPosted: Wed Dec 29, 2010 6:50 am     Reply with quote
Ok thanks! But, i dont understand something. If the bus is sending information all the time to other ECUs, why i cant hook up and "see" all the data like in a j1708 bus?

I know i have to query some PIDs because they are not transmited all the time. But, RPM, speed, etc should be transmited, right?

thanks!
collink



Joined: 08 Jan 2010
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Location: Michigan

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PostPosted: Wed Dec 29, 2010 7:12 am     Reply with quote
championx wrote:
Ok thanks! But, i dont understand something. If the bus is sending information all the time to other ECUs, why i cant hook up and "see" all the data like in a j1708 bus?

I know i have to query some PIDs because they are not transmited all the time. But, RPM, speed, etc should be transmited, right?

thanks!


It's possible. You should hook up to the OBDII port and listen in to see what is going on. However, there could be multiple buses in the car and it's likely that critical ECU functions are on a different bus that you can't see.
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Wed Dec 29, 2010 10:56 am     Reply with quote
Spot on.
Depends what you want to see. On my current car, the main ECU functions are on a fibre optic bus, as are the ABS stuff. However the basic 'engine revs, temperature, battery condition, etc.', are on the Can bus, going to the instrument panel. There are three CAN busses & two fibre optic links.

Best Wishes
Geps



Joined: 05 Jul 2010
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PostPosted: Tue Sep 27, 2011 5:56 am     Reply with quote
Ttelmah wrote:
Spot on.
Depends what you want to see. On my current car, the main ECU functions are on a fibre optic bus, as are the ABS stuff. However the basic 'engine revs, temperature, battery condition, etc.', are on the Can bus, going to the instrument panel. There are three CAN busses & two fibre optic links.

Best Wishes


Interesting....Out of interest which car is this? I've only heard of fibre optic being used in MOST bus - not between safety critical systems.
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