Which multiconductor cable/jack to use?

Discussion in 'General Electronics Chat' started by kgstewar, Oct 22, 2012.

  1. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    Hi all,

    I am nearing the end of a scoreboard project and am now dealing with the remote (wired) boxes that hold the pushbutton triggers. It's a 12V system and the pushbuttons are momentary with a little LED ring around the button. Buttons trigger CD40192 counters via a cd40106 debounce circuit so I'm imagining the current load per button is pretty small.

    The pushbutton boxes will be about 10-15 feet away from the scoreboard and I would like the boxes to plug into the main scoreboard via some kind of modular plug or standard socket but am not sure what would be a good candidate. The multiconductor cable from the pushbutton box to the scoreboard must have 9 conductors.

    I've thought about D-Sub connectors but was also wondering about modifying a USB 3.0 cable or using an RJ-50 (10P10C) connector and cable. Something like this would be convenient, but I don't know if there is a reason to not use something like this. Thanks!

    http://www.winfordeng.com/products/cbm10.php

    Kevin
     
  2. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    Or perhaps what I need to know is the answer to a more general question:

    What is the maximum distance and maximum current for a multiconductor cable that uses, for instance, 26AWG wire to deliver simple pushbutton pulses (not data)?

    Thanks!

    Kevin
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    at 10-15 feet and simply being used for low current switching virtually anything can be used.. Pick what works best for you IMO..
     
  4. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Okay, I had to refresh my memory, but if you're looking for calculations to verify what you can and cannot use, here you go:

    Look up AWG ratings - you are interested in current and resistance of the wire. One place is here: http://www.powerstream.com/Wire_Size.htm.

    You need to know the maximum current (and voltage) required by your load. Since you are sending power down a wire to a switch and back to a wire ultimately into the CD40106, the CD40106 is your load. According to the datasheet, the CD40106 will draw 0.1uA on the input. We'll add a factor of safety and say you need 1uA to go across the wire.

    Let's use 26AWG at 15 feet as an example. According to the AWG wire link, 26AWG can handle up to 2.2A for chassis wiring and 361mA for power transmission. Here I'm not real clear on the difference, so we'll stick with the smaller number, 361mA, to be safe. You need 1uA, so 26AWG will handle the current with no problem.

    The next concern is the voltage drop. Any length of wire will have resistance and effectively acts as a resistor which will drop the voltage over a long enough length.

    If this example, you need 15 feet to go from power to the switch and 15 feet to go from the switch to the CD40106 for a total of 30 feet. Referencing the AWG chart again, 26AWG has a resistance of ~0.041 per foot. Therefore: 30 x 0.041 = 1.23Ω.

    So 30 feet of 26AWG wire will act like a ~1Ω resistor. Following Ohm's law:

    E=IR
    E = 0.000001A x 1.23Ω = 1.23uV drop across 30 feet of 26AWG.

    So if you have a regulated 12.0VDC source supply power to the switch contacts, you'll see 12.0 - 1.23uV = 11.9999VDC on the input to the CD40106.

    The simple answer is yes, 26AWG will work. The long answer allows you to play with other AWG sizes and lengths to verify if they will or will not work.

    Personally I like the DB9 idea as it is relatively easy and cheap to get or make cables and solder or crimp to the mating connectors. A 10P10C could work, but I would think it will be more work to solder to the mating connector or make a break out PCB board. I don't know much about USB 3.0, but I don't think it will have enough contacts. If you plan to make your own cable, you could go with Molex connectors: http://www.radioshack.com/product/i...ce=CAT&znt_medium=RSCOM&znt_content=CT2032231

    Though those don't mount to enclosures like DB9s can.

    Hope this helps.
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Db9 with strain relief. Not the cheap db9. Remember, this is not fixed installation, people will be moving around with It and tripping on the cord, etc.
     
  6. kgstewar

    Thread Starter Member

    Apr 5, 2012
    151
    6
    Mcgyvr, elec_mech, and strantor. many thanks for your help!

    elec_mech thanks a lot for walking me through those calculations. That is a great help and I think I will follow the advice to go with DB9 cable and connectors.

    Kevin
     
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