Thread: BMMCC/BMMSC S.Bus, PWM, LANC controllers database

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  1. #11  
    Senior Member shijan's Avatar
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  2. #12  
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    just so everyone is aware there is also one big potential disadvantage of SBUS vs PWM (beyond it being harder to implement)

    Sbus sets all channels at once - ie each time you send any sbus signal it will defacto set a value for all connected control channels, even if you maybe didn't want to
    this affects more the 4 settings that take absolute values (focus, iris, zoom, audio levels) as the 4 switch type settings (iso, WB, SA and rec) effectively ignore the sbus signal unless it does something very specific that will generally always be generated quite deliberately

    So say you had a focus controller setup over sbus but also wanted to be able to use the lens barrel to tweak focus - this wouldn't work in practise as any time the controller sends a signal - any sbus signal at all even if you hadn't changed the focus control, it would override the focus as well

    another area it impacts is that those 4 values need initialised to something so everytime you turn the controller on or off you will get a reset to the initial value (though this can be avoided if the controller can remember the last setting in some sort of non volatile memory)

    quite a few people have commented on the latter behaviour when trying out the sbus library I put up for controlling the camera

    PWM can actually be more flexible here - since its only one channel per control, you don't need to change any specific channel unless you want to (though your limited to 4 channels of course, where sbus has 8 available - potentially up to 16 if BM ever decide to expand what you can control)
    Last edited by Stelvis; 05-29-2017 at 06:54 PM.
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  3. #13  
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    in terms of latency and so on the only thing that really separates PWM and SBus performance wise is:

    1.) accuracy (SBuS is digital and hence values are non ambiguous, whereas PWM relies on an interpretation of precise timing of an analogue signal) - in practise I never noticed too much of a difference here

    2.) resolution - sbus has theoretically twice the resolution of standard PWM implementations on the arduino or similar processors (which are limited by 10bit on board DACs on their analogue signal outputs) but in practise this is less as the cameras respond to a quite conservative range of values (around 300 to 1800 or so rather than the full rage of 0 to 2047). Again in the real world not a huge difference (this could potentially affect how 'steppy' focus adjustments are for example)

    while the differences in signal latency might potentially be a thing if you're flying a drone I doubt anyone would notice the difference on a simple camera controller
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  4. #14  
    Quote Originally Posted by Stelvis View Post
    yep, still working on something here
    Shijan and I have batted a few ideas back an forth...
    I would buy your handle in a heartbeat. Is there a rough timeline?
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  5. #15  
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    Quote Originally Posted by LJR View Post
    I would buy your handle in a heartbeat. Is there a rough timeline?
    not really I'm afraid - certainly on my part the grip design is a hobby and my real job often gets in the way
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  6. #16  
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    Quote Originally Posted by Stelvis View Post
    just so everyone is aware there is also one big potential disadvantage of SBUS vs PWM (beyond it being harder to implement)

    Sbus sets all channels at once - ie each time you send any sbus signal it will defacto set a value for all connected control channels, even if you maybe didn't want to
    this affects more the 4 settings that take absolute values (focus, iris, zoom, audio levels) as the 4 switch type settings (iso, WB, SA and rec) effectively ignore the sbus signal unless it does something very specific that will generally always be generated quite deliberately

    So say you had a focus controller setup over sbus but also wanted to be able to use the lens barrel to tweak focus - this wouldn't work in practise as any time the controller sends a signal - any sbus signal at all even if you hadn't changed the focus control, it would override the focus as well

    another area it impacts is that those 4 values need initialised to something so everytime you turn the controller on or off you will get a reset to the initial value (though this can be avoided if the controller can remember the last setting in some sort of non volatile memory)

    quite a few people have commented on the latter behaviour when trying out the sbus library I put up for controlling the camera

    PWM can actually be more flexible here - since its only one channel per control, you don't need to change any specific channel unless you want to (though your limited to 4 channels of course, where sbus has 8 available - potentially up to 16 if BM ever decide to expand what you can control)
    So would this mean that using the Ursa Minis grip that controls auto focus and auto iris and plugging it into something like the one little remote wouldn't work? Or would it be okay because it's a Lanc connection into the sbus?
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  7. #17  
    Senior Member shijan's Avatar
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    One more simple idea for DIY build. External PWM REC/STOP button module that fits to standard 15mm rod clamp. Endless mounting options. Maybe i'll create small batch too.




    Last edited by shijan; 10-29-2017 at 04:01 AM.
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  8. #18  
    Senior Member shijan's Avatar
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    [PWM] BMMCC Remote Control: Learn to build your own Blackmagic Micro Cinema Camera Remote by Kempton Does

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  9. #19  
    Senior Member shijan's Avatar
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    [LANC] Canon GR-V1 Camera Grip for EOS C200
    https://www.bhphotovideo.com/c/produ...mera_grip.html
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  10. #20  
    Senior Member shijan's Avatar
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