| Author |
Message |
Guest
|
 Posted:
Fri Dec 16, 2005 12:19 am Post subject:
Basic link tester |
|
|
Ok, I've seen the keychain loopback plugs that'll light the link LED on
the switch.
I need something to add to my toolbag so I know at the wall jack that I
can confirm I'm attached to the switch without having to go
upstairs/down the hall to see a light.
Right now I carry around an old hub. Plug it in and see if it's link
light lights up, to confirm connectivity. I'd like to see if there was
something a bit smaller with an LED that lights up.
Could I build one? Is there power coming over a couple of pairs that
could light a small LED on a homemade keychain loopback tester? I'm
not running power over ethernet.
How does the link light work? Is there a pair jumpered in each port of
the switch that provideds a circuit that the device on the other end
runs power over to power an LED? Does the device/switch at the other
end just complete a circuit to power the LED on your end?
TIA,
Buster |
|
| Back to top |
|
 |
Guest
|
|
| Back to top |
|
|
William P.N. Smith
Guest
|
| Posted:
Fri Dec 16, 2005 4:39 am Post subject:
Re: Basic link tester |
|
|
busterama@gmail.com wrote:
| Quote: | I need something to add to my toolbag so I know at the wall jack that I
can confirm I'm attached to the switch without having to go
upstairs/down the hall to see a light.
Right now I carry around an old hub. Plug it in and see if it's link
light lights up, to confirm connectivity. I'd like to see if there was
something a bit smaller with an LED that lights up.
|
That's pretty much your best bet. A couple of small batteries might
eliminate your wall wart...
| Quote: | Could I build one? Is there power coming over a couple of pairs that
could light a small LED on a homemade keychain loopback tester? I'm
not running power over ethernet.
|
There's no (significant) power coming from a switch.
| Quote: | How does the link light work?
|
There's a set of pulses coming from the switch (and another set coming
from your hub) that detail the capabilities of either end and let them
negotiate a common set of connection details.
[Note that having link lights doesn't tell you if the wiring is OK,
you really need a tester for that...] |
|
| Back to top |
|
|
glen herrmannsfeldt
Guest
|
| Posted:
Fri Dec 16, 2005 9:20 am Post subject:
Re: Basic link tester |
|
|
busterama@gmail.com wrote:
| Quote: | Ok, I've seen the keychain loopback plugs that'll light the link LED on
the switch.
I need something to add to my toolbag so I know at the wall jack that I
can confirm I'm attached to the switch without having to go
upstairs/down the hall to see a light.
|
I have heard that a transceiver, which is usually much smaller than
a hub, can be run off a 9 volt battery. Probably not for very long,
but long enough if you use a momentary switch that it should last for
a reasonable number of tests.
I haven't tried it, though.
Otherwise a simple CMOS circuit could detect link pulses enough to light
an LED, but I haven't done that, either.
-- glen |
|
| Back to top |
|
|
Tomi Holger Engdahl
Guest
|
| Posted:
Fri Dec 16, 2005 4:50 pm Post subject:
Re: Basic link tester |
|
|
busterama@gmail.com writes:
| Quote: | Ok, I've seen the keychain loopback plugs that'll light the link LED on
the switch.
I need something to add to my toolbag so I know at the wall jack that I
can confirm I'm attached to the switch without having to go
upstairs/down the hall to see a light.
Right now I carry around an old hub. Plug it in and see if it's link
light lights up, to confirm connectivity. I'd like to see if there was
something a bit smaller with an LED that lights up.
|
I have seen plans to build this kind of device by using
an external Ethernet transceiver module. Many transcievers
with RJ-45 connectors are a size of "match box". Accroding
some information on internet, you could take a suitable 9V
battery and feed power to power pin. With that the transceiver
LEDs shoudl work and tell you if connector works or not.
| Quote: | Could I build one?
|
Not in eany very easy way.
Enything can be built. The terter would nee practically the
same electtronics as those Ethernet transceivers...
meaning one special IC, RJ-45 connector, Ethernet m
magnetics, and some passive components... Hard to make
smaller than commercial transceivers.
| Quote: | Is there power coming over a couple of pairs that
could light a small LED on a homemade keychain loopback tester? I'm
not running power over ethernet.
|
Normal Ethernet does not supply enough power to properly light
up a LED from the power on the line. The power just when it
leaves the Ethernet card on transmitting pair could just light
a LED when you are transmitting all the time (we are talking about
around 2V signal, 10-20 mA current), when tens of meters of cable has
attenuated it then there is hardly enough power to do that..
When card/hub/switch is not transmitting, there is not much signal
on the line on the line..
| Quote: | How does the link light work? Is there a pair jumpered in each port of
the switch that provideds a circuit that the device on the other end
runs power over to power an LED? Does the device/switch at the other
end just complete a circuit to power the LED on your end?
|
The link light on the Etherner card end is connected to Ethernet
transceiver IC link output pin. The hub/switch end has some
kind of transiceiver IC functionality in it (either separate IC
or integrated as part of larger IC).
The transceiver ICs know that there is another transciver on the
line when they see some signal coming from each other.
The signal coming other end could be acgtual data, and in case
data is not coming there comes every now and then short link
pulses on 10Base-T (100Base-T system uses continuous signal
stream flowing when connection has established).
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/ |
|
| Back to top |
|
|
Tomi Holger Engdahl
Guest
|
| Posted:
Fri Dec 16, 2005 4:59 pm Post subject:
Re: Basic link tester |
|
|
glen herrmannsfeldt <gah@ugcs.caltech.edu> writes:
| Quote: | busterama@gmail.com wrote:
Ok, I've seen the keychain loopback plugs that'll light the link LED on
the switch.
I need something to add to my toolbag so I know at the wall jack that I
can confirm I'm attached to the switch without having to go
upstairs/down the hall to see a light.
I have heard that a transceiver, which is usually much smaller than
a hub, can be run off a 9 volt battery. Probably not for very long,
but long enough if you use a momentary switch that it should last for
a reasonable number of tests.
I haven't tried it, though.
|
There is one web page describing such circuit at
http://www.lausd.k12.ca.us/Jefferson_HS/td_ethtester.htm
I have not had spare Ethernet transceivers around, so I haven't
tested this myself either.
| Quote: | Otherwise a simple CMOS circuit could detect link pulses enough to light
an LED, but I haven't done that, either.
|
Even if no packets are sent on a 10BASE-T cable, a pulse has to be
sent periodically (called the "Normal Link Pulse" or "NLP"). It is
used to keep the connection "alive". A pulse needs to be sent every
16ms or so.
The link pulse must have a width of 60 to 130 nsec with a repetition
frequency of 42 to 125 Hz. Pulse amplitude should be 500 mV to 3V.
The NLP can also be replaced by a "Fast Link Pulse" (FLP) burst,
during a process called "auto-negotiation". The FLP carries
information about the capabilities of the sender, so that the hardware
at both end of a cable can negotiate the link parameters, like the
speed and the half/full duplex status.
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/ |
|
| Back to top |
|
|
Tomi Holger Engdahl
Guest
|
| Posted:
Fri Dec 16, 2005 5:03 pm Post subject:
Re: Basic link tester |
|
|
busterama@gmail.com writes:
I have not tested this particular device myself...
You can use continuety test for testing Ethertnet connections.
Take the transmitting and receiving pairs. In normal Ethernet
connection there is a transformer coils (pretty low resistance)
connected to transmitting and receiving pairs on both ends
of connection. You could use a multimeter to check this
continuety. I have used this several times for testing purposes.
Low resistance between two wires on the pair tells there is
something attached on those lines on the other end of the cable
(or cable has been damaged and shorted in the middle).
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/ |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in