Hi Hex.

26-Aug-03 08:46:12, Hex wrote to All


 H> Hi all! I was wondering if anyone would know how to make a cable
 H> tester for ethernet/phone cables? I had a few ideas come to mind,

 H> but none of them really seem like they'd be all too accurate. My
 H> theory was to make something like a wire testor (the thing you clip
 H> to one side of a wire, and touch the tip to the other side and if
 H> there's a full connection, the handle will light up) for each of
 H> the 8 wires (ethernet) with a LED for each wire. If each wire has a
 H> full connection, all the LEDs will light. The problem is, I don't
 H> think that will work very well if the wires are out of sequence,
 H> they'd still light up.

yeah, feed the wires on one end from a diode dividor chain and at the other end
light a led when the correct voltage is presented.


   +V
    |
    1k
    |--10K--> pin1
   _L_
   \./
   ~T~
    |--10K--> pin2
   _L_
   \./
   ~T~
 etc,,,
   _L_
   \./
   ~T~
    |---10k--> pin8
    |
   1K
    |
   -V


at the other end you have to use paired comparartors to check that the
correct voltage is being presented

               +V         +V
                |          |
               2K         1K
                |          |
      osc1 >----+          |----.
                |          |    `--|\______/\  /\  __
    pin1  <-----(------+---(----+--|/        \/  \/  |
                |      |  _|_   |         \\         |
                +-100K-'  \./   `--|\_____|/|___|/|__|
               _|_        ~T~   .--|/     |\|   |\|
               \./         |----|
               ~T~         |    `--|\______/\  /\  __
    pin2  <-----(------+---(----+--|/        \/  \/  |
                |      |  _|_   |         \\         |
                +-100K-'  \./   `--|\_____|/|___|/|__|
                .         ~T~   .--|/     |\|   |\|
                .  e t c   .    .
               _|_         .    .  e t c
               \./         |----|
               ~T~         |    `--|\______/\  /\  __
    pin8  <-----(------+---(----+--|/        \/  \/  |
                |      |  _|_   |         \\         |
     osc2   ----+-100K-'  \./   `--|\_____|/|___|/|__|
                |         ~T~   .--|/     |\|   |\|
                2K         |----'
                |          |

you could use LM324 op amps (you'd need 4 chips) for the voltage comparison
the circuit could be powered from a 9V batterry etc...

the oscilator inputs OSC 1/OSC2 feed a triangle wave to the divider chain
somethuing like this:   (i've forgottedn how to design them)

  |                      |
 2k .-10K-.  A           2k
  | |     |  :           |          .-10K-- osc1
  |-+-|\__|-1K---.--1K---(-|\____   |
  | .-|/         |       |-|/   |---|
  | `------------|       |--10K-'   |
  |             _L_      |    :     `-10k-- osc2
  2k            ~T~ 300n 2K   B
  |              |       |

resistor A controls the rate b controls the gain
5K and 50K trimpots could be a good choice here

about 3Hz with 7V Peak-to peak would be a good starting point

this  should cause the leds to blink if there's a broken wire/bad contact.
half a 324 could do the above.

I'm not sure how brightly a 324 can light a LED... I'm failry sure they can
manage 5ma.

diodes are all silicon small signal types(eg 1N914)

on the other hand it may be easier to use a microcontroller....

    -=> Bye <=-

---