Signal verus Voltage

[dw85745]

I have some basic questions.

Purpose:

Obtain the RPM value off of Chrylers CCD bus using ODB_I

What I've done

I've written a VB program to interface with the RS232 port using the API.

Researched the CCD bus  -- twisted pair with one wire (+), the other wire (-) -- running at 2.5 volts

I know the baud rate of the CCD bus signal.

What I think I Understand.

I believe (??) the signal is part of (i.e. rides on) the voltage.  Hence the signal -- RPM of interest -- needs to be extracted from the voltage.

Still doing research on the header and trailer bytes (or bits) and the identifying byte which will indicate that the RPM is the next data in sequence

Questions (What I don't understand)

1)   How do I connect the CCD bus to my RS232 port.?

2)  How do I go about separating the signal from the voltage so I don't kill my computer?

3)  How do I determine whether the CCD bus is putting out an analog or digital signal?

      If analog I know I'll need an analog to digital converter.

4)  Anything else that I should know but haven't asked.

Thanks

David

[HizNI]

Do you have any specs on the CCD bus or ODB_I?

[dw85745]

Sure:

http://www.cnblogs.com/shangdawei/p/3570499.html

[HizNI]

Hey dw,

It looks like the CCD uses a CAN interface. You will not be able to read it with an RS232 unless you have a CAN to RS232 converter, and I don't know how the information will be sent on that. NI also has some options for CAN devices to USB interface, found on this page:

http://sine.ni.com/nips/cds/view/p/lang/en/nid/203382

As far as how the CCD and CAN bus actually work, the information is contained in the voltage differences between the high and low line. According to the link you sent, 

"the CCD data bus systems translate a small voltage difference as a one (1), and a larger voltage difference as a zero (0)." Reading further, it says that a difference of 0.02 volts between the lines is a 1 and 0.1 volts is a 0. Because it communicates by seeing if the difference is small (1) or large (0), the signal is digital. 

What NI hardware/software are you using?

[dw85745]

HiZNi

Thanks for responding.

[quote]

What NI hardware/software are you using?

[/quote]

None right now.  Just trying to do some basic research to see if what I want to do is feasible.

[HizNI]

dw,

It should be as long as you get the CAN to RS232 connector or a CAN card. 

Best of luck to you!