I/O switching board

Discussion in 'The Projects Forum' started by SheffGruff, Nov 4, 2008.

  1. SheffGruff

    Thread Starter New Member

    Jul 30, 2008
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    0
    Hello,

    I have a conveyor belt system which is soon to have two PLCs able to control it. At present it is only designed to be controlled by one PLC.

    I need to design a circuit that allows switching for a set of 11 24V in and 11 24V out circuits on a single switch. The aim is simply to use 1 switch to select which PLC's I/O is fed to the machine.

    The machine in use is this: http://www.bytronic.net/html/ict_3.html

    Can anyone give me starting suggestions on the best way to approach this switching problem? A 22-pole switch seems a little bit inelegant and unlikely!
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can control them by using only 6 switches, a 6 to 64 decoder chip and MOSFET's or relays for the switches. How you want to control them exactly?
     
  3. SheffGruff

    Thread Starter New Member

    Jul 30, 2008
    8
    0
    One of the PLCs will always be providing the control.

    I need to be able to switch sensor inputs and PLC outputs from Logic Controller "A" to "B" using a single switch. Its quite similar to a domestic A/V matrix or computer peripheral switcher in concept.

    The PLCs are wired to get 11 inputs and send 11 outputs out to the hardware - one of the PLCs will have good programming in it, the other is for students to experiment with. The idea is that students can try out their own program, then flip a switch to see how the normal PLC handles things.

    These inputs and outputs are fed on 15 pin D connectors, so I need to make a board that has a switch, two connectors that feed out to hardware and two connectors for each of the 2 PLCs 15 pin D connectors (ie four D-subs in and two out, with routing controlled by a switch).
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can use 11 small DTSP relays for the inputs and 11 DTSP relays for the outputs whose power ratings depend on the load on the output.
    For the input relays you will connect the signal going to the input of the PLC to the common pin of the relay (for each PLC input) and then use all the normally closed contacts for the first PLC and the normally open contacts for the second PLC. When the relays are non-activated the inputs will be fed to the first PLC and when the relays are energized the input signal will be fed to the second PLC.
    For the outputs do the same and use a single switch to turn on and off the relays.
    If you are familiar with transistors you can so it with FET transistors.
     
  5. SheffGruff

    Thread Starter New Member

    Jul 30, 2008
    8
    0
    Seems obvious enough really, thinking relays may be slightly more expensive than a solid-state solution but that seems the simplest solution to it. Have considered using opto-isolators and switching their power supply as well but that seemed a bit OTT.
     
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