Multiconductor cable question

Discussion in 'General Electronics Chat' started by kgstewar, Jan 7, 2013.

  1. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    Hi all,

    I am using the following 10-conductor cable to connect some remote pushbuttons to an electronic scoreboard. I am using 9 conductors for different pushbuttons (most connect to ground; a couple connect to 12V) and 1 conductor for 12V. Here is my question:

    Can I use the "drain" wire in the cable to connect to the ground wire of my power supply? That would effectively give me 11-conductors, which is really what I need.

    Thanks!

    Kevin


    http://www.allelectronics.com/make-a-store/item/10CS22/10-CONDUCTOR-SHIELDED-CABLE-W/DRAIN/1.html
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Depends on the specific application and length of cable. How much power will be drawn from the 12v supply?
    Yes, using the shield as GND is ok, except in some specific cases this might not be acceptable.
     
  3. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    This cable will be about 10 feet long, at the most. Total power will always be less than 20 watts. I've measured the current at 1 amp for a few seconds (when mechanical bell is ringing) = 12 Watts; and current draw is normally about 0.7 amps = 8 or 9 watts. (assuming I did my calculations correctly)

    Thanks!

    Kevin
     
    Last edited: Jan 7, 2013
  4. MrChips

    Moderator

    Oct 2, 2009
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    15 to 20W @12V is about 1-2A.
    In this case I would suggest no. You should provide separate POWER and RETURN line for 2A.
     
  5. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    Thanks for your help, I'll go with a separate cable for the power and ground.

    Kevin
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    Why not? Seems your cable actually has a nice shield wire to use, not just the foil which is not good to work with.

    For noise immunity reasons it's good practice to ground that line anyway.

    #22 AWG will have about .3 ohms in the round trip over 10 feet (20 feet total) so I would not worry about losses in the cable.
     
  7. BReeves

    Member

    Nov 24, 2012
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    Agree, wouldn't think twice about using that cable for what you want. It will work just fine..
     
  8. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    Hmm, so maybe worth a try...

    Thanks!

    Kevin
     
  9. MrChips

    Moderator

    Oct 2, 2009
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    As I said, a lot depends on the situation. Try it and it will most likely work.
    What to look for? If you have high current switching on and off on the power and ground lines, this will be coupled into the other signal lines. It depends on what the other lines are used for and how sensitive and critical they are to the correct functioning of the system.
     
  10. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    Thanks Mr Chips,

    Seven of the conductors in the cable will connect pushbuttons that are connected to GND and feed into CD40106 debouncers which then feed into cmos counters (CD40192 and CD4518). Two of the conductors in the cable will connect pushbuttons that send 12V to the reset pins in the cmos counters. That leaves one of the conductors for the 12V supply, and then the "drain" wire for supply GND. I'll hook it up and see if my counters start acting funny.

    Thanks again!

    Kevin
     
    Last edited: Jan 7, 2013
  11. MrChips

    Moderator

    Oct 2, 2009
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    Ok. No harm done in trying. If it causes problems you can always fall back on a separate power cable.
    My suspicion is that the debouncer, pushbutton and reset signals will be sensitive to power transitions.
     
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