SATA Dock Select Switch

Discussion in 'The Projects Forum' started by Art, Sep 26, 2013.

  1. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    Hi Guys,

    I have a USB dual SATA dock that can boot from bay A if both bays are populated with drives,
    or if only one bay is populated, it can boot from bay A or bay B
    (whichever bay the drive is in).

    The problem for me is both are bootable drives, and I want to be able
    to leave them both in the dock, and select either of them to boot from.
    So I'm considering using a rotary double pole switch to switch both
    5 & 12 Volt supplies between drives.
    I checked the drives don't need the 3.3 volt supply on the SATA connector.
    I assume at the moment, they are both always connected to power.

    Then it occurred to me I could have a third (middle) position on the rotary
    switch as an option to connect both drives to the power, just in case I want an operating system to see both drives.
    Is this the circuit I want (where the middle position selects both drives) ?

    [​IMG]

    Please forgive the crudity of my design.
    There are no transistors, they are diodes that turned out that way.
    It was an early version of Protel before they had computers :)
    Cheers, Art.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,151
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    Why not handle this in software?

    And I don't understand what you're trying to do with the diodes. They will drop voltage and your drives may not like that.
     
  3. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    The diodes are to provide power to both drives in the switches middle position.
    If I just connected them straight together, the switch wouldn't work.

    It's not software, it's the way the dock works.
    It can only boot from bay A if both bays are populated,
    but I want to leave both bays populated, and boot from either bay (by turning one drive off).
     
  4. wayneh

    Expert

    Sep 9, 2010
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    OK, I think I'm beginning to grasp this. With the right switch and configuration, you won't need the diodes. I'll see if I can find or draw up an example. Someone will likely beat me to it, and that'd be great!
     
  5. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
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    Thanks. It's a two pole rotary switch where you can set the number of positions
    mechanically between 2 and 6, where I have it set to 3.
    The position of both switches must be the same for this reason.
    (whereas the diagram looks like two different switches).
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Are you married to that switch? I'm not sure it'll work. Do you have a link to it?
     
  7. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    It would take something much sexier to cheat on it.
    I will post naked photos.

    Seriously, I would give up the idea of using both drives at once,
    to wire it the simple way I think, and be limited to one or the other.
    (unless there was something really nicer out there.
     
  8. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
  9. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
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    Since the drive has the ability to turn it's own motor on & off
    (obviusly some circuitry in there to switch the 12 Volt)..
    would it be acceptable just to switch the 5 volt supply?
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,151
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    It's quite possible. You might get a better answer on an overclockers forum.

    But switching both shouldn't be hard - just another pole. Getting the right arrangement is just a logic puzzle. Draw it out and you'll find the solution. Then figure out if that switch you have can do what you need.
     
  11. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    I am happy to be limited to one drive or the other,
    but have had to opt for two seperate switches due to space limitation
    inside the case.

    It doesn't matter if I wreck the dock (preferably not a HDD with it),
    but it is not often that I make any modification to a facia panel of something
    without butchering it, and this time I got it right :)

    It's for SPST switches only to switch 5V, so I'm going to test on a single HDD
    first to see if it does what I want.
    (no switching at computer's run time, only before it's boot).



     
  12. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    Fair to follow up and conclude because who knows who might be looking later on.
    Works like a charm so far :)
    Just switching the 5 Volt supply does indeed kill the HDD motor as well.

    I did try switching both drives in and out at run time, and works as expected.
    When a drive is turned on it will pop up in explorer, and the usual window asking
    what you want to do with the drive you just inserted.

    The only hiccup is when both drives are on, and you turn one drive off,
    both drives become disconnected momentarily, and the one that remains powered kicks back in.

    Seems like some interruption in the supply from the other drive switching off interrupts it.
    Maybe a capacitor across the supply line would help with that?

    Normally though, as I said, It will only be switched before the computer is started.
    I will post back if everything burns at some stage... otherwise it continued working, and I'm happy :D
     
  13. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Can you show a diagram of how you have the switch connected right now?
    Yes some largish capacitors in front of the disks should help with the power dropout.
    Or you could get a make-before-break version of the switch, that one should not have this problem.
     
  14. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    In the end I couldn't fit the rotary switch in the case,
    so I just used independent SPST switches on each drive's 5 Volt supply.
    Nothing more fancy than that.

    In the dual SATA dock, both drive's 12 & 5 Volt supplies shared the same source,
    so I had to cut a few tracks to isolate them, and then some scraping to make pads
    to connect the switches.

    [​IMG]

    The rotary switch was supposed to go on the side, and move from front to back.
     
    Last edited: Sep 28, 2013
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