Forums

cable tester

Started by David Lesher April 17, 2020
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
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
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."
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
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.
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.
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
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
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