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Ask an Expert Forum Design suggestion for a bus
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Design suggestion for a bus

amgalbu
amgalbu over 10 years ago

Hello

I need to develop a custom board (hardware + software) to drive a set pneumatic valves. The requirements are

  • the boards can be stacked (up to 18 boards can be stacked, but I expect this number to be increased in the future)
  • the boards must be configuration-free (no dip-switches to set the board address)
  • the bus must be fault-tolerant: if a board in the stack breaks, the other boards should continue to work properly
  • pneumatic valves are "digital", so the bus must convey only on/off commands

An external board communicates with the stacked boards through the bus and drives each pneumatic valve indivudually

 

The only solution I can think of is to have two serial buses: the first one is an in-out bus used only to configure the address of each board in the stack and is used only when the system is switched on. The second bus connects all the boards in parallel, thus providing the required fault-tolerance

 

However, this solution is far from being elegant... Does somebody have a better idea?

 

Cheers

Ambrogio

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Top Replies

  • crjeder
    crjeder over 10 years ago in reply to Robert Peter Oakes +1
    I2C adressability is an issue. E. g. a suitable device could be TPS22993 Quad Channel Load Switch with GPIO and I2C Control but it features only 3 adress pins for a max of 8 devices. But each can operate…
  • Robert Peter Oakes
    Robert Peter Oakes over 10 years ago +1
    Then by that measure, using a device like a 23017 http://ww1.microchip.com/downloads/en/DeviceDoc/21952b.pdf would give 16 valves on a board and re duce the count of boards considerably and only needs…
Parents
  • peterjcs23
    peterjcs23 over 10 years ago

    if the backplane pcb can supply the address/enable at each location, you only need the single parallel connected bus. The bus pcb should also provide the short circuit protection and over-volts protection at each location.

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  • crjeder
    crjeder over 10 years ago in reply to peterjcs23

    Yes, was thinking the same. But that (allone) would not faciliate the failover capability. (unless I missed something)

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  • crjeder
    crjeder over 10 years ago in reply to peterjcs23

    Yes, was thinking the same. But that (allone) would not faciliate the failover capability. (unless I missed something)

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  • clem57
    clem57 over 10 years ago in reply to crjeder

    Use dual rings that run in opposing directions for fault tolerance. Send tokens to address each board to request an address like DFHP.

    Clem

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  • amgalbu
    amgalbu over 10 years ago in reply to clem57

    Hi Clem

    Thanks for the suggestion. The dual ring option probably will not even require to assign an address to each board: the token may contain an "hop counter" which is decremented by each board before passing it. I will check with the customer if adding an "end-of-line jumper" (to close the second loop) is acceptable

     

    Cheers

    Ambrogio

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  • amgalbu
    amgalbu over 10 years ago in reply to amgalbu

    Comment to myself image

    The dual ring unfortunately does not cover the "more-than-one-board-broken" condition!

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  • peterjcs23
    peterjcs23 over 10 years ago in reply to crjeder

    Yes, was thinking the same. But that (allone) would not faciliate the failover capability. (unless I missed something)

     

    It's not too difficult to protect the bus, use a fault tolerant drive such as LT1791.

     

    If you need to detect which board is faulty, you can provide an ACK feedback bus.

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  • Robert Peter Oakes
    Robert Peter Oakes over 10 years ago in reply to amgalbu

    This would fail if a single board fails and the ring is re-initialized

     

    you say each board has an actuator of some kind attached and I assume each one is for a specefic purpose, so if one fails and re-initialization occures then assignements are now changed, unless all valves serve the same purpose, you must know the address of each valve in order to correctly control it

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