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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

Parents

  • I2C only supports 127 Devices on a single bus, without I2C switches etc, you will not be able to change this, also it would be quite complex to make this fault tollerant . Also I2C devices have factory assigned addresses within a range, some can be changed enough to provide say 16 devices of the same make and brand on a bus but not much more. I2C probably is not your answer if you need 80++ boards stacked, all uniquely controllable and fault tollerant.

     

    RS485 as mentioned earlier would be better, it is cheap, can easily cover the distance and number of devices and can be made into a ring, dual rings etc with little cost.

     

    None of this though willl address how each board will self configure and allow the control master know who is who for specefic control purpose

     

    Does each one need to be uniquely identified and controlled ?, can you say the purpose of the solution with a little more detail ?

Reply

  • I2C only supports 127 Devices on a single bus, without I2C switches etc, you will not be able to change this, also it would be quite complex to make this fault tollerant . Also I2C devices have factory assigned addresses within a range, some can be changed enough to provide say 16 devices of the same make and brand on a bus but not much more. I2C probably is not your answer if you need 80++ boards stacked, all uniquely controllable and fault tollerant.

     

    RS485 as mentioned earlier would be better, it is cheap, can easily cover the distance and number of devices and can be made into a ring, dual rings etc with little cost.

     

    None of this though willl address how each board will self configure and allow the control master know who is who for specefic control purpose

     

    Does each one need to be uniquely identified and controlled ?, can you say the purpose of the solution with a little more detail ?

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