EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: ftransform on February 06, 2013, 11:30:50 am
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So I ordered some 24 gauge 4 wire double shielded cable with a aluminum foil and copper braid. I am looking to buy connectors but I am completely unfamiliar with how shielded wire connectors work. Is it like a BNC cable connector with four pins? Or is it just a tight screw for the braid and then the inner wires are loose inside of the enclosure with say header connector?
Digikey has an extremely intimidating connectors list and I am not sure where to start looking.
My application involves DC signals by the way.
Other talk about shielded cable is appreciated in this thread by the way. I'm guessing that the foil is soldered to the braid and the braid is soldered around the connector at the connection point?
Is it possible to make a useable connector by perhaps drilling out a BNC connector and routing the 4 wires through the middle while still soldering the braid to it? The connection would be made and THEN the wires would be soldered to the PCB inside the case. It would make cable disconnection impossible without opening the case and desoldering (or perhaps screw terminals??) but it would give a solid ground connection of the shield to the enclosure which would be connected to earth ground.
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Something like this? http://www.rapidonline.com/Cables-Connectors/Circular-locking-multipole-connectors-66501 (http://www.rapidonline.com/Cables-Connectors/Circular-locking-multipole-connectors-66501)
or these: http://www.rapidonline.com/Cables-Connectors/Connectors-Mains-Power/Sensor-Connectors (http://www.rapidonline.com/Cables-Connectors/Connectors-Mains-Power/Sensor-Connectors)
or the good old XLR connector: http://www.rapidonline.com/Cables-Connectors/Black-Finish-XLR-Cable-Plugs-518877 (http://www.rapidonline.com/Cables-Connectors/Black-Finish-XLR-Cable-Plugs-518877)
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5 pins lockable din connector is ok for that kind of things. 4 wires + 1 ground
http://www.ebay.com/sch/i.html?LH_TitleDesc=0&_sacat=0&LH_PrefLoc=2&cmd=Blend&_nkw=5+din+connector+lock&cmd=Blend (http://www.ebay.com/sch/i.html?LH_TitleDesc=0&_sacat=0&LH_PrefLoc=2&cmd=Blend&_nkw=5+din+connector+lock&cmd=Blend)
(http://thumbs2.ebaystatic.com/d/l225/m/m312rpW0TaRMaY5kSd2GvIA.jpg) (http://thumbs3.ebaystatic.com/d/l225/m/mT50l8qwmiGNH9mLCxXjzLQ.jpg)
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or the good old XLR connector: http://www.rapidonline.com/Cables-Connectors/Black-Finish-XLR-Cable-Plugs-518877 (http://www.rapidonline.com/Cables-Connectors/Black-Finish-XLR-Cable-Plugs-518877)
I will try to avoid 3 pin XLRs for applications that are not related to audio. This can lead to big mistakes.
4, 6 and 7 pin are used in a lot of applications, and there isn't a strict rule. 5 pin are "reserved" to lightning control using DMX protocol.
Do not use XLRs for a permanent connection (they will become intermittent after some time (months or years)), XLRs are intended for multiple connect/disconnect use, and are very reliable in this case.
For permanent connection, round DIN connectors, like the ones in the above post, are more reliable (the female contact is actually gas-tight, once a round male pin is inserted) and cheaper.
That's the reason for using DIN connectors in fixed PA systems (e.g. churches sound systems) and XLR connectors in touring PA systems.
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Lemo connectors are very good.
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Lemo connectors are very good.
Extremely good! With a price tag to match!
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Lemo connectors are very good.
Extremely good! With a price tag to match!
And very finicky to assemble too!
Amp's CPC (Circular Plastdic Connector) line is worth a look.
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Hirose do similar connectors to Lemo
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So I ordered some 24 gauge 4 wire double shielded cable with a aluminum foil and copper braid. I am looking to buy connectors but I am completely unfamiliar with how shielded wire connectors work. Is it like a BNC cable connector with four pins? Or is it just a tight screw for the braid and then the inner wires are loose inside of the enclosure with say header connector?
No, it isn't going to be controlled impedance. It will just be 4 wires, wrapped in foil, and covered over by the braid. Depending on the specific cable, the wires might be twisted in pairs but probably not.
Digikey has an extremely intimidating connectors list and I am not sure where to start looking.
True. This is one of the few times I really still prefer to have a paper catalog. It is much easier to page through looking for something that "looks right".
Other talk about shielded cable is appreciated in this thread by the way. I'm guessing that the foil is soldered to the braid and the braid is soldered around the connector at the connection point?
Typically a metal connector will have some sort of clamp for the shield inside the connector body. You just clamp a bit of the braid against the housing which provides the ground connection. No soldering should be required. If you have both a signal ground and a chassis ground, you would connect the signal ground through one of the wire conductors, and the chassis ground to the shield.
Anyway, I also recommend the 5-pin DIN connectors.
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Should I connect the shield to earth ground ( I am not sure how this will be housed yet) or should I connect it to the DC ground?
I ask because I experimented with shielding a breadboard using huge metal bowl. When I connected the bowl to the earth ground on my PSU there was no real reduction in noise. However when I connected the bowl to the DC ground the noise was reduced by two orders of magnitude. I am inclined to connect it to the DC ground because of this but I would like to hear opinions.
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or the good old XLR connector: http://www.rapidonline.com/Cables-Connectors/Black-Finish-XLR-Cable-Plugs-518877 (http://www.rapidonline.com/Cables-Connectors/Black-Finish-XLR-Cable-Plugs-518877)
I will try to avoid 3 pin XLRs for applications that are not related to audio. This can lead to big mistakes.
4, 6 and 7 pin are used in a lot of applications, and there isn't a strict rule. 5 pin are "reserved" to lightning control using DMX protocol.
Do not use XLRs for a permanent connection (they will become intermittent after some time (months or years)), XLRs are intended for multiple connect/disconnect use, and are very reliable in this case.
For permanent connection, round DIN connectors, like the ones in the above post, are more reliable (the female contact is actually gas-tight, once a round male pin is inserted) and cheaper.
That's the reason for using DIN connectors in fixed PA systems (e.g. churches sound systems) and XLR connectors in touring PA systems.
XLRs are used, & have been for many years,in Broadcasting in applications where they may not be moved for years,as well as in those
where they are often plugged & unplugged.
They are equally reliable in both appllications.
Cheap,nasty,XLRs will show problems,but quality connectors will last for decades.
DIN connectors,in my opinion,are fiddly,messy annoying things,& I would only use them if I had to.
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Cheap XLR's will give you problems over time.
XLR's from major players (Neutrik (http://www.neutrik.us/en-us/xlr/), Switchcraft (http://www.switchcraft.com/Category.aspx?Parent=684)) will work problem free for years, especially if you choose the gold plated contacts.
I have many in my studio that have been patched to the same place for years and have no issues.
4 pin XLR's are quite common for 12vdc power connections on portable gear, typically wired pin 1 to gnd, pin 4 to +12v.
As mentioned, Hirose (http://www.hirose-connectors.com/connectors/H203SeriesCategorySearch.aspx?cat=01) and LEMO (http://www.lemo.com/en/products?tid_i18n=All) are excellent connectors as well and are heavily used as interconnects in pro audio and on high end film/digital cameras.
They do take some patience to terminate.
Fischer (http://www.fischerconnectors.com/) are another robust, albeit pricy, option and are often found on older ARRI cameras and JL Fisher dollies.
Belden (http://www.belden.com/) is somewhat of a standard for cable and Clark makes a shielded DMX cable (http://www.clarkwire.com/cableDMX-Pro.htm) that might fit your application.
Generally the foil is left as close to the connector as possible, but only the drain wire is attached to the ground pin. Some people also choose to tie the ground pin to the shell contact present on some connectors so the metal housing becomes part of the shielding.
IMO, I'd go with the 5 pin XLR unless you fear there's a chance of your project being mixed into a lighting control environment and being confused for DMX, in which case you could use a 6 pin XLR and just leave one pin unterminated.
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Cheap XLR's will give you problems over time.
XLR's from major players (Neutrik (http://www.neutrik.us/en-us/xlr/), Switchcraft (http://www.switchcraft.com/Category.aspx?Parent=684)) will work problem free for years, especially if you choose the gold plated contacts.
I have many in my studio that have been patched to the same place for years and have no issues.
4 pin XLR's are quite common for 12vdc power connections on portable gear, typically wired pin 1 to gnd, pin 4 to +12v.
As mentioned, Hirose (http://www.hirose-connectors.com/connectors/H203SeriesCategorySearch.aspx?cat=01) and LEMO (http://www.lemo.com/en/products?tid_i18n=All) are excellent connectors as well and are heavily used as interconnects in pro audio and on high end film/digital cameras.
They do take some patience to terminate.
Fischer (http://www.fischerconnectors.com/) are another robust, albeit pricy, option and are often found on older ARRI cameras and JL Fisher dollies.
Belden (http://www.belden.com/) is somewhat of a standard for cable and Clark makes a shielded DMX cable (http://www.clarkwire.com/cableDMX-Pro.htm) that might fit your application.
Generally the foil is left as close to the connector as possible, but only the drain wire is attached to the ground pin. Some people also choose to tie the ground pin to the shell contact present on some connectors so the metal housing becomes part of the shielding.
IMO, I'd go with the 5 pin XLR unless you fear there's a chance of your project being mixed into a lighting control environment and being confused for DMX, in which case you could use a 6 pin XLR and just leave one pin unterminated.
HAHAHHAHAHA I can see a super stoned technician in a lightning control environment plug my ohm meter into a lightning rod ?
I don't know what a DMX is or what its used for in a lighting environment (unless you mean the rap artist) but that would be pretty hilarious. !
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DMX is a protocol used for control over light and music ( or something like that, I'm not into audio)
XLR connectors are used on many audio/light/stage equipment.
The Tektronix E plugin ( uV scope plugin) uses a 3 pin XLR. I must say, they are more comfortable to solder as Lemo connectors.
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I use something that goes on ebay, aliexpress etc as 'xlr aviation connector'. Those are the connectors which are commonly used to connect microphone to CB-radios. I never actually managed to find this connector type frem "major" manufacturer like Amphenol or Neutrik
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I second CPC connectors. But one thing to watch out for with those, and probably a whole lot of other connectors like that, is you really need the proper tool to crimp the pins. You are in for a world of trouble if you try to use a pair of needle nose pliers or something to do those crimps. If the crimps don't come out the right size the connection will be terrible and the pin probably won't fit in the housing. You don't necessarily have to spend the 200 usd for the name brand crimper, but you at least need a tool that is close to the same shape.