two-way telemetry

Discussion in 'General Electronics Chat' started by jlangho, Feb 27, 2012.

  1. jlangho

    Thread Starter New Member

    Oct 22, 2011
    So I'm a bit hazy on the subject, but let me lay everything out first and then we can go form there.

    I've got two devices on a can bus logging data and talking back and forth. I can talk to them both over the CAN bus with a CAN to usb converter provided by the manufacture. For tuning purposes I'd like to take that physical connection out and do it wirelessly, basically a wireless can bridge.

    Since I'm not doing any data modification shouldn't i be able to use a uC that has a Can txvr and output it to a wireless module that will be received by another wireless module that will talk to a uC and have it put back on a can bus where i will plug in my can to usb adapter?

    I haven't had any communications classes yet so its all a bit uncertain and other than knowing what can is and the basics i don't know

    or better yet, since I'm not doing anything with the CAN data, could i grab a txvr that takes a high/low signal like the can uses and just have it bridge that way?
  2. magnet18

    Senior Member

    Dec 22, 2010
    CAN buses are usually used in vehicles if im not mistaken
    are you using this in a vehicle?
    if so, what kind?
    If it's automotive, we wont be able to talk about it on here
  3. jlangho

    Thread Starter New Member

    Oct 22, 2011
    yaya...everyone so uptight around here...understandably though, don't want anyone to pile into a wall.

    It on a University FSAE car. The ECU in question is a motec M84 thats talking with our aim data logger. Everything on the car is student built and designed so I don't see this being an issue for what I'm assuming the "no automotive" policy is.

    I did a little more research on the subject. here's a datasheet with the motec protocol:

    The only thing I'm questioning now is that the fact that they're what looks like a 64 bit wide address. If i get a 32bit uC I'm not entirely sure how the CAN/SPI will handle that 64 bit value at the address.

    Also I've found what seems to be a pretty decent txvr:

    I'm planning on doing this interrupt driven since the txvr's have a dedicated interrupt line. once the can buffer gets an input packet I'd send it out to the SPI, do a CRC calc and send it out. On the other end I'd wait for a receive on the txvr and then interrupt and drive it through the spi to do the crc in the uC. once everythings kosher i could spit it back out to the can.