cable tester

[David Lesher]

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[John Larkin]

On Fri, 17 Apr 2020 18:58:05 +0000 (UTC), David Lesher
<wb8foz@panix.com> wrote:

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`

I've just put 1% resistors on both ends to make a zig-zag series
string. Check that with a good DVM. That will catch most errors.

Or a rotary switch/battery/resistor (or pushbuttons) on one end and N
led's on the other.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Robertson]

On 2020/04/17 12:35 p.m., John Larkin wrote:

On Fri, 17 Apr 2020 18:58:05 +0000 (UTC), David Lesher
wb8foz@panix.com> wrote:

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`

I've just put 1% resistors on both ends to make a zig-zag series
string. Check that with a good DVM. That will catch most errors.

Or a rotary switch/battery/resistor (or pushbuttons) on one end and N
led's on the other.

The trick is finding shorted leads. The best tester I've had for cables
(ribbon, etc.) created an algorithm of a good cable, then used it to
verify other cables. The down side was you had to program it each time
you turned it on - battery life isn't great I think. Old tech. But it
checks up to 80 pins/leads for continuity, cross shorts, etc..

https://www.digchip.com/datasheets/parts/datasheet/1772/ACT-FLAT-R.php

There are many others out there. The nice thing about the Assman is you
can plug in home-made adapters to the 80 pin ports on the rear.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[Ricky C]

On Friday, April 17, 2020 at 2:58:10 PM UTC-4, David Lesher wrote:

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

Doesn't a terminated cable mean it has resistors built in? Wouldn't that cause another pin to be excited?

When checking pins for "no signal" you could add a resistor to ground with a matching value resistor and verify half the voltage. So each pin will see one of three values, zero signal, full signal or half signal.

Stimulate with a 3 Vpp signal to make sure the terminating resistor wasn't actually a diode by mistake. I had that happen once where the internal termination in a cable wasn't a resistor.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Tom Del Rosso]

Ricky C wrote:

Doesn't a terminated cable mean it has resistors built in? Wouldn't
that cause another pin to be excited?

Terminated witha a connector, as opposed to bare wire.

 

[Pimpom]

On 4/18/2020 12:28 AM, David Lesher wrote:

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`

I bought a cheap Chinese RJ45/RJ11 cable tester about 10 years
ago and traced the circuit. I haven't used it much but it worked
when I tested it. It uses a counter to scan each line in turn.
It's like this one
https://tinyurl.com/yc2whyr2
I could post the schematic if you think it might help.

 

[Ricky C]

On Saturday, April 18, 2020 at 1:11:19 AM UTC-4, Pimpom wrote:

On 4/18/2020 12:28 AM, David Lesher wrote:
A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`


I bought a cheap Chinese RJ45/RJ11 cable tester about 10 years
ago and traced the circuit. I haven't used it much but it worked
when I tested it. It uses a counter to scan each line in turn.
It's like this one
https://tinyurl.com/yc2whyr2
I could post the schematic if you think it might help.

The aliexpress ads are ok, but when I checked for this on eBay I found multiple people saying they crap out after just a few uses. I guess you can't make decent connectors that cheap. The eBay listing shipped in US and also included a pouch while the aliexpress listings seem to have much longer than usual deliveries. One was 30 to 50 days!

If they were any good I would order a couple. But if it's going to crap out after a few uses, why bother shipping trash half way around the world?

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Clifford Heath]

On 18/4/20 5:35 am, John Larkin wrote:

On Fri, 17 Apr 2020 18:58:05 +0000 (UTC), David Lesher
wb8foz@panix.com> wrote:

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`

I've just put 1% resistors on both ends to make a zig-zag series
string. Check that with a good DVM. That will catch most errors.

It doesn't tell you when you have mixed-up pairs, like in an Ethernet
cable where you have a blue/orange pair and an orange/blue pair.

You need a tester to show you the cross-talk for that.

CH

 

[Pimpom]

On 4/18/2020 11:30 AM, Ricky C wrote:

On Saturday, April 18, 2020 at 1:11:19 AM UTC-4, Pimpom wrote:
On 4/18/2020 12:28 AM, David Lesher wrote:
A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`


I bought a cheap Chinese RJ45/RJ11 cable tester about 10 years
ago and traced the circuit. I haven't used it much but it worked
when I tested it. It uses a counter to scan each line in turn.
It's like this one
https://tinyurl.com/yc2whyr2
I could post the schematic if you think it might help.

The aliexpress ads are ok, but when I checked for this on eBay I found multiple people saying they crap out after just a few uses. I guess you can't make decent connectors that cheap. The eBay listing shipped in US and also included a pouch while the aliexpress listings seem to have much longer than usual deliveries. One was 30 to 50 days!

If they were any good I would order a couple. But if it's going to crap out after a few uses, why bother shipping trash half way around the world?

There's always that factor of reliability with cheap Chinese
products and that of long shipping times when you order from
AliExpress unless you opt for an expensive courier delivery. But
you can't beat the price and some of their products are very
good. It's a matter of personal choice.

For example, I bought a true RMS 20,000-count DMM with all the
bells and whistles and a claimed DC accuracy of 0.05% for US$28
in 2018, and a 6000-count model for $14 before that. I've used
Chinese DMMs exclusively for the past 25 years and they last at
least 5 years with heavy everyday use with the occasional drops
and other abuse.

In any case, I offered the schematic to the OP in case the idea's
useful for adaptation to his requirement.

 

On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
<no.spam@please.net> wrote:

On 18/4/20 5:35 am, John Larkin wrote:
On Fri, 17 Apr 2020 18:58:05 +0000 (UTC), David Lesher
wb8foz@panix.com> wrote:

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`

I've just put 1% resistors on both ends to make a zig-zag series
string. Check that with a good DVM. That will catch most errors.

It doesn't tell you when you have mixed-up pairs, like in an Ethernet
cable where you have a blue/orange pair and an orange/blue pair.

I think modern Ethernet doesn't care.

You need a tester to show you the cross-talk for that.

CH

The resistor thing usually does; the snipped LED thing certainly does.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Ricky C]

On Saturday, April 18, 2020 at 3:11:47 AM UTC-4, Pimpom wrote:

On 4/18/2020 11:30 AM, Ricky C wrote:
On Saturday, April 18, 2020 at 1:11:19 AM UTC-4, Pimpom wrote:
On 4/18/2020 12:28 AM, David Lesher wrote:
A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`


I bought a cheap Chinese RJ45/RJ11 cable tester about 10 years
ago and traced the circuit. I haven't used it much but it worked
when I tested it. It uses a counter to scan each line in turn.
It's like this one
https://tinyurl.com/yc2whyr2
I could post the schematic if you think it might help.

The aliexpress ads are ok, but when I checked for this on eBay I found multiple people saying they crap out after just a few uses. I guess you can't make decent connectors that cheap. The eBay listing shipped in US and also included a pouch while the aliexpress listings seem to have much longer than usual deliveries. One was 30 to 50 days!

If they were any good I would order a couple. But if it's going to crap out after a few uses, why bother shipping trash half way around the world?


There's always that factor of reliability with cheap Chinese
products and that of long shipping times when you order from
AliExpress unless you opt for an expensive courier delivery. But
you can't beat the price and some of their products are very
good. It's a matter of personal choice.

For example, I bought a true RMS 20,000-count DMM with all the
bells and whistles and a claimed DC accuracy of 0.05% for US$28
in 2018, and a 6000-count model for $14 before that. I've used
Chinese DMMs exclusively for the past 25 years and they last at
least 5 years with heavy everyday use with the occasional drops
and other abuse.

In any case, I offered the schematic to the OP in case the idea's
useful for adaptation to his requirement.

Yep, I bought a programming adapter for $25 off ebay or aliexpress, don't remember which, they are largely interchangeable. The one from the FPGA maker is $200 now. The $20 one works great!

But good equipment is definitely the exception. So you pay your money and take your chances. You can always dispute a charge on the credit card.

I like eBay a lot better because their dispute policy works well. I bought several flash sticks on aliexpress and as each one arrived I tested it only to find it was fake. I got a full refund on the first. A partial refund on the second. The third they demanded I video the 12 hour test and send it to them, so I got zip. Had to use the credit card dispute to resolve the last two.

From now on it has to be a pretty big bargain I can't get on eBay for me to use Aliexpress. That's rare.

I'm definitely not going to buy crap devices from aliexpress.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Clifford Heath]

On 18/4/20 5:28 pm, jlarkin@highlandsniptechnology.com wrote:

On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

On 18/4/20 5:35 am, John Larkin wrote:
On Fri, 17 Apr 2020 18:58:05 +0000 (UTC), David Lesher
wb8foz@panix.com> wrote:

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`

I've just put 1% resistors on both ends to make a zig-zag series
string. Check that with a good DVM. That will catch most errors.

It doesn't tell you when you have mixed-up pairs, like in an Ethernet
cable where you have a blue/orange pair and an orange/blue pair.

I think modern Ethernet doesn't care.

On the contrary, it cares more than ever before.

The four pairs all have different twist rates to cancel cross-talk
between the pairs. If you make two wrong pairs by splitting two pairs
then neither pair will work, and both will interact with the other two
pairs. You might get 10MBit out of your GB Ethernet, but you're unlikely
to get 100, and you definitely won't get GB speeds.

CH

 

[Jasen Betts]

On 2020-04-18, Pimpom <nobody@nowhere.com> wrote:

On 4/18/2020 12:28 AM, David Lesher wrote:
A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`


I bought a cheap Chinese RJ45/RJ11 cable tester about 10 years
ago and traced the circuit. I haven't used it much but it worked
when I tested it. It uses a counter to scan each line in turn.
It's like this one
https://tinyurl.com/yc2whyr2
I could post the schematic if you think it might help.

It's "the 555 and CD4017 circuit" driving LEDs both ends of the cable.
for this application the CD4017 data sheet explains to to extend the
circuit to more than 10 outputs.





To automate it you could put 4017s at both ends of the cable clocked
with the same clock and with a reset arrangement to synchronise them

(Q0 of the master 4017 to reset on the slave )

but only power one of them, Any significant current on the ground or
vcc pins of the powered 4017 will indicate crossed or shorted wires

The unpowered 4017 will have voltage on the VDD pin (via the
protection diodes on the clock input or the MOSFETs on the outputs)
if that goes away there's an open circuit

A diode arrangement could be used to maintain a lower VDD if you're
worried that the unpowered 4017 might lose its state. (I'm not)

--
Jasen.

 

On Sat, 18 Apr 2020 18:02:24 +1000, Clifford Heath
<no.spam@please.net> wrote:

On 18/4/20 5:28 pm, jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

On 18/4/20 5:35 am, John Larkin wrote:
On Fri, 17 Apr 2020 18:58:05 +0000 (UTC), David Lesher
wb8foz@panix.com> wrote:

A friend asked me about cable testing. He has a need for a tester
for terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`

I've just put 1% resistors on both ends to make a zig-zag series
string. Check that with a good DVM. That will catch most errors.

It doesn't tell you when you have mixed-up pairs, like in an Ethernet
cable where you have a blue/orange pair and an orange/blue pair.

I think modern Ethernet doesn't care.


On the contrary, it cares more than ever before.

The four pairs all have different twist rates to cancel cross-talk
between the pairs. If you make two wrong pairs by splitting two pairs
then neither pair will work, and both will interact with the other two
pairs. You might get 10MBit out of your GB Ethernet, but you're unlikely
to get 100, and you definitely won't get GB speeds.

CH

So buy good cables.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Tom Del Rosso]

jlarkin@highlandsniptechnology.com wrote:

On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

It doesn't tell you when you have mixed-up pairs, like in an Ethernet
cable where you have a blue/orange pair and an orange/blue pair.

I think modern Ethernet doesn't care.

What it doesn't care about is when a twisted pair goes from pins 1-2 to
pins 3-6 at the other end, and 3-6 to 1-2.

 

[Tom Del Rosso]

jlarkin@highlandsniptechnology.com wrote:

On Sat, 18 Apr 2020 18:02:24 +1000, Clifford Heath
no.spam@please.net> wrote:

The four pairs all have different twist rates to cancel cross-talk
between the pairs. If you make two wrong pairs by splitting two pairs
then neither pair will work, and both will interact with the other
two pairs. You might get 10MBit out of your GB Ethernet, but you're
unlikely to get 100, and you definitely won't get GB speeds.

CH

So buy good cables.

The issue is whether the wires are on the right connector pins. Pins 3
and 6 should be a twisted pair. You have to sense crosstalk to see if
pins 3 and 6 are on wires of two different pairs.

 

On Sat, 18 Apr 2020 07:54:06 -0400, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 18:02:24 +1000, Clifford Heath
no.spam@please.net> wrote:

The four pairs all have different twist rates to cancel cross-talk
between the pairs. If you make two wrong pairs by splitting two pairs
then neither pair will work, and both will interact with the other
two pairs. You might get 10MBit out of your GB Ethernet, but you're
unlikely to get 100, and you definitely won't get GB speeds.

CH

So buy good cables.

The issue is whether the wires are on the right connector pins. Pins 3
and 6 should be a twisted pair. You have to sense crosstalk to see if
pins 3 and 6 are on wires of two different pairs.

Right. No simple tester is going to find pair crosstalk errors.

I did a *lot* of TDR/TDT testing on various cat5/6 cables, for a
system that mis-applies them to, basically, SPI data at unreasonable
distances and rates. They are all over the place.

Some people even vary the twists on cables that have individually
shielded pairs! That adds prop delay skew for no reason.

It's a mess to use cat-cables for anything fast except ethernet
itself, which usually does active equalization and doesn't care much
about skew.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

On Sat, 18 Apr 2020 08:03:59 -0400, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

It doesn't tell you when you have mixed-up pairs, like in an Ethernet
cable where you have a blue/orange pair and an orange/blue pair.

I think modern Ethernet doesn't care.

What it doesn't care about is when a twisted pair goes from pins 1-2 to
pins 3-6 at the other end, and 3-6 to 1-2.

Don't do that, and don't expect any simple tester to report that. It
would have to accurately measure 3-terminal mutual capacitances or
something. UTP would be especially tricky. Are there affordable
testers for that?

If a cable in your network doesn't work for whatever reason, throw it
away.

I wonder when such a wiring error would really trash ethernet packets.
For some lengths and rates, it might not.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Tom Del Rosso]

jlarkin@highlandsniptechnology.com wrote:

On Sat, 18 Apr 2020 08:03:59 -0400, "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

It doesn't tell you when you have mixed-up pairs, like in an
Ethernet cable where you have a blue/orange pair and an
orange/blue pair.

I think modern Ethernet doesn't care.

What it doesn't care about is when a twisted pair goes from pins 1-2
to pins 3-6 at the other end, and 3-6 to 1-2.




Don't do that, and don't expect any simple tester to report that. It
would have to accurately measure 3-terminal mutual capacitances or
something. UTP would be especially tricky. Are there affordable
testers for that?

What I described is a simple crossover cable. (Xmit pair to Rcv pair and
Rcv to Xmit.) Any cheap tester can report that. I have a $5 one that
does. But it can't detect split pairs that Cliff described.

You must be describing something else but what?

If a cable in your network doesn't work for whatever reason, throw it
away.

I wonder when such a wiring error would really trash ethernet packets.
For some lengths and rates, it might not.

I saw a Cisco IP phone (the top brand after all) that would not connect
with a single intermittent wire in the brown pair, which is an optional
pair. It tried to connect at 1 Gbps with 4 pairs and when it failed it
would not revert to 100 Mbps on 2 pairs. So I disconnected the blue and
brown pairs and it worked fine with only the other two.

 

On Sat, 18 Apr 2020 18:49:57 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 18 Apr 2020 20:43:47 -0400, "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 08:03:59 -0400, "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

It doesn't tell you when you have mixed-up pairs, like in an
Ethernet cable where you have a blue/orange pair and an
orange/blue pair.

I think modern Ethernet doesn't care.

What it doesn't care about is when a twisted pair goes from pins 1-2
to pins 3-6 at the other end, and 3-6 to 1-2.




Don't do that, and don't expect any simple tester to report that. It
would have to accurately measure 3-terminal mutual capacitances or
something. UTP would be especially tricky. Are there affordable
testers for that?

What I described is a simple crossover cable. (Xmit pair to Rcv pair and
Rcv to Xmit.) Any cheap tester can report that. I have a $5 one that
does. But it can't detect split pairs that Cliff described.

You must be describing something else but what?

I was thinking Cat5/6 ethernet cable, with three pairs. Same problem
of detecting switched wires that preserve DC continuity.

Oops, 4 pairs of course.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard