Yes, you can make several possible arrangements with the wires, and one
good example is just using always return jumpers at the end of the cable
(as a loop back connector), so you can control everything from this
side. The use of a nice multicontact relay at this side can allow you to
simple connect all pairs in a single long pair that loops back as
another pair, so you can measure also losses in high frequencies and
more using a simple comparison of amplitude/frequency received. Remember
that electric signals travel aprox at 5ns/m... you could measure the
cable length.
Wagner

Andre Abelian wrote:
>
> Holger,
>
> A few months ago I made similar simple tester for RJ45 network cable.
> without searching the net looking at other designs I figured the
> quickest way to check wires will be by pair.
> we have 8 wire that means  4 pairs.
> this is how I did it .
> attached is the  source code
> I didn't even use crystal RC is good enough.
>
> 4 green LED's  and 4 red LED's
> power on reset all LED's will turn on to make sure all of them ok
> to determine the start 1p, 2p, 3p, 4p  I turned all green LED's on then
> it will turn on one by one  if  polarity is wrong  red will
> turn on if open then no light. the schematic I have in ORCAD format.
> all together took me about 2 hours to do it. as far as hardware you
> do not need any diode.
>
> Let me know about it.
>
> Andre Abelian.
>
> Holger Morgen wrote:
>
> > Hi -
> >
> > I'm building a cable tester for 8 wire UTP, cat III - V (normal 10Mb/s
> > network cables) up to 100m.
> > Using a 16F84 I am wondering if I should use any ESD prevention.
> >
> > My setup looks something like this: (plz. use a Courier font)
> >
> > ----+      -- +5V                  -- +5V  +---
> > 16F +      +                       +       +16F
> > 84  +    Diode                   Diode     +84
> >     +      +                       +       +
> > RBx +--1K--------Twisted cable-----+---1K--+Rbx
> >     +      +                       +       +
> >     +    Diode                   Diode     +
> > ----+      +                       +       +---
> >            -- GND                  --GND
> >
> > The 1K resistors are not for ESD, but I may "short-circuit" 2 or more pins.
> > My question is: Are the diodes needed?
> > I have read (page 23, note 2 in Microchips F84 manual) that
> > "I/O pins have diode protection to VDD and VSS".
> > But can I trust that? Are they strong enough for an ESD discharge?
> >
> > /holger
> > hmo@q8.dk
>
>   ------------------------------------------------------------------------
>                  Name: Cable2.asm
>    Cable2.asm    Type: application/x-unknown-content-type-asm_auto_file
>              Encoding: base64