RE: CAN Inspector: a CAN node to sample the CAN bus waveforms

Hi Michael,
Interesting project idea.

The first question I'd ask would be who gets this information and how do
they get it?

I'm guessing that one of the CAN nodes has an external connection to the
outside world and there's no way to add functionality to it in the form of
an scope module?  

For example, I have a project that has 3 CAN bus channels, one that talks to
a proprietary battery management system, one that uses CANOpen and works
with a number of both custom and COTS CANOpen modules and finally one that
speaks J1939 for communication to the vehicle.

Access to the controller is via an FTDI USB device into a PC which in turn
is connected to the outside world.  How I've not been told.  Wifi Ethernet?
Remote Desktop?   Doesn't really matter.

My controller has two extra CAN ports so I could add a module like the one
you describe to work independently from the potentially ailing CAN buses.
My controller can be expanded to also have a WizNet Ethernet module so some
sort of Ethernet Scope/Meter could also be used.

Since the client has a PC connected I could even use a USB scope device on a
hub that talks to my controller and the scope.   

The problem you face is if your CAN bus is crippled due to a physical issue
any scope device that is on the same CAN bus becomes useless.  

Perhaps you could add some details as to how you would report the bus
information?

Thanks
John Dammeyer




> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Michael Ashley
> Sent: March-12-16 3:47 PM
> To: [email protected]
> Subject: [CANLIST] CAN Inspector: a CAN node to sample the CAN bus
> waveforms
> 
> 
> Dear CAN bus gurus,
> 
> I've been thinking of a design for a CAN node that is able to digitize the
> waveform on CANH and CANL and then transmit the waveform as multiple
> CAN messages. The device would also be able to report the CAN power
> supply voltage. I'm interested in your opinions on this concept.
> 
> The design is based around the Texas Instruments ADC08B200 ADC, which
> digitizes to 8-bits at up to 200 Msps. Its key feature is a 1 kB data
buffer that
> can be read out slowly, so there is no need for the MCU to keep up with
the
> data in realtime.
> 
> The motivation for wanting such a device is that I'm using a CAN bus for
> some remote experiments in Antarctica, and there have been several cases
> recently where the bus has operated in a degraded mode (CANL shorted to
> ground, missing terminator - this is on a 70m long bus running at 100
kbps)
> without anyone being awareof it. The people who are servicing the
> equipment do not have the expertise or the time to connect up TDRs or
> oscilloscopes or even multimeters to diagnose problems. The physical
> environment can be very tough, e.g,. -40C in summer (-80C in winter) and
> high altitude (over 4000m), so asking someone to connect an oscilloscope
> and make measurements is asking a lot. The personnel are only on-site for
> betwen 5 and 21 days over summer each year; the rest of the time the
> equipment is entirely remote.
> 
> A "CAN Inspector" node that could be simply placed on the bus would be
> very valuable. I could remotely monitor the bus, recognise when problems
> occur, and give repair instructions. An alternative approach could be a
small
> USB-accessible oscilloscope.
> 
> One of the big advantages of CAN is its fault tolerance. However, if the
fault
> occurred some years ago, and you are already running in a degraded mode,
> then you have already used up all your tolerance.
> 
> I will post a link to a draft schematic for the CAN Inspector in a
subsequent
> message.
> 
> Regards, Michael
> --
> Professor Michael Ashley                   Department of Astrophysics
> University of New South Wales       http://www.phys.unsw.edu.au/~mcba
> --
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