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Design suggestion for a bus

amgalbu

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

  • in reply to dougw

    Never trust a human !! (to replace only one node at  a time).

     

    Actually with the pass though fail safe this system wouldn't be too bad - if two nodes were replaced it would break but would know that it had been broken so could demand re-configuring.

     

    Here's an interesting challenge:

     

    If you had a set of Doug-nets, where in each one the nodes are in a different order - is it possible to design it so that two (or more) nodes can be replaced and the system still recovers correctly ? And if so how many nets  are needed and how must they be scrambled to correctly recover from any pair of nodes replaced ?

     

    MK

  • in reply to amgalbu

    Each Actuator needs to know its position, this implies some kind of configuration, either through physical design or something else, If a board fails then it may not seem to be in the system (Depending on failure mode) so another board may assume its logic position if there all identical and therefor appear to the conrol system as a differnt valve to what was before the failure. this could be a big poblem

     

    you want fault tollerance such that any board failing will not stop the rest, this implies a parallel buss of some sort (Even if the data is serial), having the buss go into a board, then out to the next will break the system if the board is pulled or fails in a bad way. If the buss is parallel and un-broken if any board is pulled out for repair / replaement then there is no way for the master controller to know its position or function without some kind of local configuration, this could be through jumpers on the connector, switches on the board, programming from a aux port ont he card... something that allows the boards itentity to be known. You state all boards must be identical and auto configure with no intervention... htere has to be something that makes each position unique and known to the board. This imples configuration in some way, even if it is supplied via the connector the board is plugged into but your saying this is not acceptable

     

    These requirements are in contradiction with each other... hense... IMPASS.

  • in reply to dougw

    Hi Douglas

    the external watchdog looks like a good idea... I need to check whether it meets cost and board size constraints but it's something that can be easily implemented and can give a good reliability to the whole system

     

    Thanks!

     

     

    Ambrogio