Ribbon Cable Tester (Installed)

Discussion in 'The Projects Forum' started by tomartig, Jan 23, 2014.

  1. tomartig

    Thread Starter New Member

    Jan 23, 2014

    I service scanning equipment that has 37 pin ribbon cable in a flex track. We often have problems with intermitten shorts and opens. I am looking to make a 2 piece cable tester. On transmitter and one reciever so I can hook them up to each end and them move the scanner back and forth and look for intermittents. A latching type indication would be great. I need the 2 boxes to be independent of eachother as they may be as far as 30 feet apart at times. Any suggestion would be greatly appreciated.
  2. John P

    AAC Fanatic!

    Oct 14, 2008
    I can imagine something with a microcontroller at each end of the cable, one to send and one to receive. The sending unit would transmit a coded signal on each of the conductors, and the receiver would monitor its inputs and give some kind of indication that the cable was or wasn't working properly. If you wanted, you could have the receiver connected to a laptop via USB, and then you could get some combination of readout on the screen, audio output, and/or a record kept in a file.

    It's a little trickier, but you might have the processor at the sending end of the cable be powered over the cable itself, so you wouldn't need a power supply or battery, but perhaps that isn't worth doing, if the unit could simply run off a couple of AA cells.

    A lot depends on how often this rig would be used, which gives an idea of how much effort it's worth putting into building it.
  3. ronv

    AAC Fanatic!

    Nov 12, 2008
    Do you need to know which pin is bad or just that you have an open or short? If just go no go it might be fairly easy to do it in only hardware (logic). Opens are easy, you can just have a plug at one end to tie each wire to the next and at the other end input a signal to the first pin then do the same with the remaining pins. What you put in the first pin should come out the last pin. Shorts are harder as you need to drive each pin and make sure it is the only one to respond.
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
    I think that strantor, a regular of this forum, posted something in line with that task.
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    I just find constructing a simple LED setup is sufficient.. Let the cable be one leg of a battery/resistor/led circuit. Battery at one end of the cable and a LED/resistor box at the other. LED lights up..no problems. if not..open
    Or create a loopback box for the end and test a bunch or all at the same time.
    If the result is to replace the whole cable if any issues are found just loopback them all and a single led gives the go or no-go
  6. tubeguy

    Well-Known Member

    Nov 3, 2012
    Adding to this, to detect shorts.
    Connect one wire to the next at the far end using equal value resistors. Then feed the near end with a constant current source. You would have a predetermined voltage drop through a good cable, but single or multiple shorts would show up as a lower voltage drop.

    Edit: Add a buzzer 'cause I know for me an intermittent would be easier to catch audibly than on an LED and definitely easier than on a meter.
    Last edited: Jan 23, 2014
  7. RichardO

    Well-Known Member

    May 4, 2013
    A coworker once built a pair of very simple testers for ribbon cables. These testers only give a go/no go indication but they are easy to build.

    I don't have time to draw the wiring right now so I hope the verbal descriptions will work:

    To test for short circuits, he made a test plug that wired all of the even pins together and all of the odd pins together. If any two adjacent wires in the cable are shorted then there will be conductivity between the even and odd sets of wires.

    He did a similar scheme to test for an open. He made two test plugs. They were wired to connect all of the wires in the cable in series. If any wire in the cable is open then there wil not be conductivity between pin 1 and the wire on the other edge of the cable.