AoE x-Chapters - 1x.1 Wire-&-Connectors

Ground currents are not a crazy idea, I've fixed some 'bad layout' done by someone else, by thinking about the return current. (There are lotsa silly ideas about ground) GH

George H.

Sorta. I don't have a problem with SMTs for board-to-board and light internal cabling. The key enabler being that it's not fiddled with by the user, and that it's not bearing a lot of force especially during vibration

Your perspective may be skewed even further in the direction of super high reliability, like, multiple decades. The above is adequate for ~1 decade automotive customers. Consumer junk of course uses SMT-exposed-to-user connectors all the time, and barely get a year.

So, some discussion on reliability versus technology versus application might be worthwhile. There can be no one answer!

Heh... if the pins mate properly; Joerg has a story about that. :-)

Speaking of... come to think of it, they're usually tin plated pins, aren't they? In a ENIG hole, say? Isn't that prone to fretting?

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

I'll be 60 late next month, so a few strippers would be apropos--just don't tell my wife. Maybe they could jump out of a cake. ;)

I generally use Xcelite flush cutters, which are far better than the usual axe-blade dikes. I also have the usual spade lug crimper / bolt cutter/ wire stripper tools. I don't like the big clunky strippers that mechanically sense the insulation and adjust their blades accordingly--I just want insulation to do as it's damn well told, and Teflon doesn't, in so many, many ways.

Cheers

Phil Hobbs

Ground currents are a thing, I agree, but HoJo knows a lot less about them than he lets on. A PCB has a lot of fast distributed capacitance, which covers a multitude of sins.

Star grounds in fast mixed signal systems, now _that's_ a disaster.

Cheers

Phil Hobbs

Using multiple smallish parallel wires between connectors adds ballasting resistance that equalizes pin currents.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Depends. SMD panel/bulkhead connectors, I agree in general, but there are some that grip the board edge pretty well. For moderate frequencies, I mostly use cast-zinc BNCs that have survived the stomp test: put the unit in a bench vise, attach a BNC cable you never want to see again, let it droop on the floor, and stomp on it. The cable should fail at the connector, and the board should be fine.

Minimum standard student-proofing.

You like wire wrap better than soldering?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Tin whiskers.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

1x.1.4.A: Free resistance? That sounds useful! ...Ah, may want to add a note that copper's tempco is _deplorable_, to discourage that creative use (or, at least, make it understood that your use will have to be a bit more creative in turn). :-)

Hanging parenthesis in 1x.1.5 (instrumentation cable).

Worth noting that 1x.1.6.A is doing the same thing that's already been covered: impedance. Zo goes as the ratio of inductance and capacitance, Zo = sqrt(L/C). And if you know the velocity factor, mu_r or e_r, you know the L and C of the transmission line. So in the same way that you can know or look up trace impedances, and their inductance or capcaitance, at a glance, so too it works for cables.

Or put another way, it seems odd to me, or unfair even, that there's a subsection on inductance, but not capacitance, or not both in general (impedance).

May be worth noting that, even though multiconductor cable isn't intended for transmission line purposes, it still has some impedance; might be an opportunity to emphasize why it's generally undesirable to do so (i.e., coupling).

Give or take whatever's referred to the transmission line section proper, of course (appendix H?).

Footnote 16 -- to be even more precise, it's a boundary condition and wave problem, like all EM problems, I suppose; in an infinite cylinder the solutions are not actually exponential, but Bessel functions. For this reason, you can get current density going to zero at some depth, then popping up below there /in the opposite direction/! (delta is still the figure of proportion that feeds the Bessel function, so it's still close enough to exponential for the engineer's hand-wave.) Not very useful for cabling, but it's interesting for industrial induction heating anyway.

Likewise, for flat plates, you get interference from the waves penetrating the front and back sides (if currents are arranged to flow there; think coplanar waveguide but with copper thickness way higher than width?), leading to nulls and opposite peaks towards the center.

The pure exponential case is only for a semi-infinite block, of course; for d >> delta, the geometry doesn't really matter, and we can still use this figure. It's just that weird things happen for d ~ delta.

Anyway.

Oh, and this is alluded to later (footnote 19), nevermind. :-) Subsection 7 and 8: well, you beat me to it I see. :^)

1x.1.10 -- Digi-Key should be hyphenated I think?

"DC power entry" connectors -- usually called barrel connectors? Also, can't figure out the "blue hexagon".

I'm fond of Molex SL and KK series headers for general connector-to-board use, or pluggable headers like OSTOQ025450 for higher currents/voltages. MT as noted is fine too, but beware of the reliability of IDC headers. (IDC ribbons seem alright, or at least, there aren't many better termination alternatives so you're kind of stuck with it; but I wonder if IDC-to-loose-wires is worse than to ribbon-of-wires?)

M12 and such circular connectors are very popular for industry (especially where IP67 and such ratings are desirable), if a bit pricey for general application; not to mention the notoriously expensive, finely crafted Turck and Lemo types.

Interesting to plot banana jacks for transmission; but, was this at 50 ohms? I wonder how they do in, say, a 200 or 300 ohm system. And, balanced, obviously. Might be the perfect connector for twin lead, eh? (Checked the reference but I don't see this data on it.) Heh, nevermind the mechanical (mere friction fit, no retention) or environmental limitations... :^)

Cheers! Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/ 

"Winfield Hill"  wrote in message  
news:qi97k80st2@drn.newsguy.com... 
> Here's a DRAFT copy of x-Chapter 1x.1, which starts 
> things off, by dealing with wire and connectors. 
> Comments and corrections please. 
> 
> https://www.dropbox.com/s/kz335xwvl5v8gie/1x.1_Wire-%26-Connectors_DRAFT.pdf?dl=1 
> 
> 
> --  
> Thanks, 
>    - Win

The worst part about it is, star grounding _is_ excellent, but it has to be the correct topology.

Sawing up grounds, ain't it. Routing signals between spokes, ain't it.

Placing signal grounds together, routing signals with ground, in a star fashion, is the way to be.

Classic example, the ground loop currents in an SMPS section create a voltage drop across the area; so, route the input and output terminals off to a single side (as opposed to straight across), where they can exit over the same common ground area. Place your filter here. CM noise is *gone*.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

True, But those great Meanwell power supplies come with Tin molex headers.

Cheers

Signal integrity is easy. PCB layer 2 is solid ground plane. Bolt it, and grounded connector shells, to the metal box in as many places as possible.

Cable shields to the box ditto.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Not really. Suppose there's a huge noisy inverter in the box. Ground loop currents once again. Cables simply tied "shields to the box", and PCB "bolt[ed] ... to the metal box", draws those currents into both. Now your precision ADCs are all reading trash.

But with visibility to where the currents are flowing, or with a star-grounding scheme, those loop currents stay separate. Say the connectors are clustered on a front panel, shields grounded to it. That keeps outside noise out, good. Collect the interior cables (which are still all grounded to the same point, preferably as coaxially as possible, no weedy wire links), and bundle them into a single harness. Ferrite beads as needed. They go over to the PCB, which no longer needs chassis ground at all.

Or do the brute-force method and use welded chassis compartments to keep the bignasty away from the quietstuff. Cost doesn't much matter in your test equipment, but it's a very real tradeoff in production. Production even likes to avoid metal if they can...

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

AFT.pdf?dl=1

be the

as

failure item, when mechanics is omitted

I guess mechanics is the point here - his first three items are all mechanical devices. I still find mechanical switches to be somewhat more

reliable than electrolytic caps.

John :-#)#

I can't recommend insulation displacement connections - after about ten to twenty years they start to fail due to (assumption here on my part) gradual displacement of the insulation leading to the wire strands losing their stiffness and the connection becomes iffy as the strands displace.

John :-#)#

I'll be 60 a few months after you. I already have my strippers! They're Teledyne thermal and cope fine with Teflon and dialled back with any other insulation devised.

piglet

Regarding that circled capital L in footnote 21: Litzendraht as a German noun should indeed be uppercase, so the current footnote is correct (potential disagreements about capitalisation of the loanword in the body copy notwithstanding).

? David

Tinned Whiskas...

Cheers

--
Clive

Did a few fine-wire end preps, with 40 gage gold in PTFE jacket. Scalpel, microscope, patience. And some extra wire length, just in case.

Wise. When my customers want me to build something with some expensive part ($700 for a 488-nm laser diode, for instance), I always tell them I want one to use and one to blow up.

Cheers

Phil Hobbs (Who almost never blows them up, but the odd time....)

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com