Get MOST Into Your Pi

When looking the modify a passenger vehicle, the Controller Area Network (CAN) bus is a pretty easy target. In modern vehicles it has access to most of the on-board systems — everything from the climate control to the instrument cluster and often even the throttle, braking, and steering systems. With as versatile as the CAN bus is, though, it’s not the right tool for every job. There’s also the Media Oriented Systems Transport (MOST) bus which is increasingly found in automotive systems to handle multimedia such as streaming music to the stereo. To access that system you’ll need to approach it slightly differently as [Rhys] demonstrates.

[Rhys] has been working on replacing the dated head unit in his Jaguar, and began by investigating the CAN bus. He got almost everything working with replacement hardware except the stereo, which is where the MOST bus comes into play. It provides a much higher bandwidth than the CAN bus can accommodate but with almost no documentation it was difficult to interact with at first. With the help of a Raspberry Pi and a lot of testing he is able to get the stereo working again with a much more modern-looking touchscreen for control. It is also able to do things like change CDs in the car’s CD player, gather song information from the CD to display on the panel, and can perform other functions of the infotainment center.

For more detailed information on the MOST bus, [Rhys] also maintains a website where he puts his discoveries and other information he finds about this system. Unfortunately car stereo systems in modern vehicles can get pretty complicated these days, but adapting car stereos in older vehicles to modern technology carries some interesting challenges as well.

14 thoughts on “Get MOST Into Your Pi

    1. Pretty spot on, it’s made me realise the MOST bridges which cost upwards of £500 have an insane markup! But if that’s all there is, then not a great deal can be done!

      There is a bunch of OEM focused information nicely hosted on the Most Cooperations website, all open and available, links in the project!

  1. This is very cool, MOST documentation is all but non existant and its been around in decent use since the 2000’s (in my experience as an autospark) Its always annoyed me how when one node fails in the loop, the whole bus goes down, NO.1 troubleshooting tool then becomes a fiber-optic loop and diagnosis by substitution until the dead module is found.

  2. He calls it ‘dated’ I call it period correct, audio is probably high quality and the knobs probably are as well.

    On the bright side his work will probably let me install that stereo in other classic cars. Or keep the (seperate?) Amplifier with speakers intact and run a different or hidden head unit with the steering wheel controls.

    I agree the proper display is simple and red for night driving. Miss my 89 e30 :'(. That cockpit was like a 1980s jet fighter.

    1. My apologies, reading his project I see that there is some kind of touchscreen controlling things like heated seats. That sounds horrible. On the plus side if his actual head unit has enough ( unused) control buttons he may be able repurpose them to control his seats etc.

      Touchscreen for car controls should be illegal. Its really quite nuts.

      1. Agreed. Luminous distractions inside the car need to go. Last night I encountered the latest from Uber. What looks like 1watt or more of blue-white LED light is inside quarter sized brick of a sign sitting on the dash. The ends and part of the rear are lit up in translucent plastic. I had a cordial talk with the driver and warned him of driving at night sight-impaired and told him to bring this up with Uber.

        Years ago there were briefly under-dash 8 tracks that had built-in psychedelic color organ lighting. Briefly. Lately I’ve rode in cars with bright blue background aftermarket motorized touchscreen stuff hanging out of the dash hole. Fragile as hell but not as much as victims on the street.

  3. MOST is still around and exists in a coaxial-cable variant too, which I’ve dealt with a lot, and a twisted-pair variant which I’ve only barely touched. Bitrates vary, but the protocol is the same regardless.

  4. I want a CD changer emulator that plugs in place of late 90’s to early 00’s Ford 6 disc CD changers. Pop in an SD card with 6 folders each holding up to 99 MP3s. Control with original head unit buttons.

    There are kits to connect an analog stereo input to hook up a phone (but most of them no longer have headphone jacks) or music player, but then you have to use the phone etc to change the tracks.

    594 songs are plenty enough for most people. I can’t come up with 594 songs I like enough to want to listen to over and over.

    I have seen CD changer emulators that go in place of the changers Ford used *after* the model they had around the turn of the century, but I don’t know if those can be adapted to the older cars and trucks.

  5. the head in my truck is dead,so I built a wireing harness
    from a hands free headset,1/8 plug and spark tested the the factory wireing harness useing a 9 volt battery
    and found the speakers,an aftermarket high impedence
    input power amp,and now there is music from my phone,and I can take calls
    built a shelf where the head was and thats where the phone sits

    next is usb power and the abilityn to tether a lap top for
    more options and work related ,umm,work

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