=== Roy,
=== THANKS for the excellent reply!
=== MY current responses are intermingled, BELOW, and marked with "==="s .
=== - Tom Gootee
Date: Fri, 20 Aug 2004 16:25:24 -0400
From: "Roy J. Tellason" <
rtellason@...>
Subject: Re: RE: making vias (was: Re: Plating thruholes.)
I'm just gonna toss out a few thoughts coming to the fore, based on me
working on all sorts of stuff over several decades, mostly repairs...
=== Great! "Repairs" usually tell the true tale...
On Friday 20 August 2004 03:41 pm, Thomas P. Gootee wrote:
> There are several possibilities that I have considered:
>
> 1) pin headers on each pcb, with ribbon cables running to similar headers
> on the front panel's new pcb, or
Pin headers are good reliable connectors, particularly if shrouded connectors
are used, and if they're also using ejector levers there isn't much stress
on the cabling.
> 2) card-edge connectors on the front panel pcb, along the bottom, that each
> of the three pcboards' edges could plug into, or
I think less well of card-edge connectors. You'll have problems with tarnish
on the card, and lack of reliability eventually with the connectors over
time. Notice that card-edge was the way to go with the old 5.25" and 8"
floppy drives, and early hard drives as well. Nowadays _all_ 3.5" floppy
drives and all IDE and SCSI hard drives use pin connectors. That should tell
you something. :-)
=== Point taken. But all of the PCs that I've seen still use card-edge connectors
=== for all of the CARDS, i.e. the PCBs, in the expansion slots (e.g. ISA,
=== EISA, PCI, etc). The "slots" are just card-edge connectors. I have
=== some that are over 15 years old that still work fine. Also, I check out
=== and/or service or refurbish a lot of old Tektronix and other test equipment,
=== much of which uses card-edge connectors (e.g. Tek 7000 series scope
=== plug-ins and Tek TM500-series plug-ins). And those are heavily used, i.e.
=== they typically undergo MANY mating/unmating cycles over their lifetimes.
=== Occasionally there is a mechanical alignment problem, or somesuch, that
=== causes problems. But not "too" many! And a lot of that stuff is at least 20 or
=== 30 years old. (Then again, maybe all of the mating/unmating cycles HELPED
=== keep the card-edge connectors in better shape (by scraping the surfaces).
> 3) right-angle headers or sockets on each pcb, that would plug directly
> into straight headers or sockets on the front panel pcb (pin headers and
> sockets, or DIN, or even D-Sub), with NO CABLING necessary, or
Pin headers at both ends of the connection is workable, provided you can
arrange the layout of stuff to accomodate this without too much trouble, but
it's gonna be a real hassle to design, compared to using cables.
=== Well, the boards are ALREADY sitting at right angles to the front panel,
=== with their edges just about in the right positions. And I guess the on-board
=== part of the re-design would be about the same as if I were using cables.
=== It seems like eliminating anything, especially %$#! cables, would be
=== "a ∗GOOD∗ thing".
===
=== But HEY! Couldn't I use the backplane/buss idea, but with pin headers and
=== sockets, instead of card-edge connectors? I just REALLY like the idea of
=== using PCBs instead of wires and cables!
> 4) another new board, a "motherboard", in the bottom of the enclosure, with
> card-edge sockets, along with a total redesign of the current boards'
> layouts, so they could be mounted vertically, in the MB's sockets, and a
> new front panel pcb that would also plug into a card-edge socket on the new
> motherboard, or
Putting aside card-edge for a minute (see above :-), what you suggest here is
called a backplane. It's been used in a few computers, and in other
equipment, both in instances where all connectors were the same, and all
signals were bussed (see the early Zenith Data Systems XT-class machines for
example) and in earlier stuff where each connector was different and you
could only plug one board in to one particular slot (see "Digital Group"
early pre-PC computers for an example of this). The biggest problem I see
with this is that you don't want all signals bussed because there are likely
to be different signals used on each board, and the other way means that any
changes makes for a redesign needed and difficulty in upgrades, etc. should
anything change in the future. Personally I'd avoid this.
=== Well, in general, you're probably right. But, in THIS case, I think it would
=== be great. Basically, the one main board and the new front panel board have
=== LOTS of things that they need to share, like multiple 2P6T switches' wiring, and
=== a 1P12T switch's wiring, and a couple of 4P3T switches' wiring, and various
=== other controls' wiring, plus signals in and out, etc, and, of course, the power
=== supply rails, and all of the separate ground paths, and probably some other stuff
=== that I'm forgetting to mention. Then there's the power amplifier board, which
=== only shares the wiring to one side of one of the same 2P6T switches, plus a
=== couple of i/o signal paths, and, of course, the power supply rails and some
=== ground paths. The third and last original board is just the power supply. And
=== all of the boards need to get power rails and separate ground paths, etc, from
=== the power supply board. I just can't see ∗anything∗ wrong with putting them all
=== on a nice big buss. Of course, the buss would have quite a few spare positions,
=== for future additions. I'd probably also have at least one spare board position,
=== for the same reason (just so I wouldn't have to change it, if another board was
=== ever added).
===
=== Am I missing something?? Or is my thinking wrong, about that, somehow??
===
=== I ∗DID∗ find some sources for fairly-inexpensive pcb-mount pin headers and
=== sockets, as well as pcb-mount card-edge connectors. So the cost of all of the
=== connectors, either pin-type or card-edge, for use on a parallel-buss pcb with
=== 62 or more traces, and six card positions (I would only ∗need∗ 5, assuming my
=== main board is split into two boards so it would fit vertically into the same cabinet,
=== which is only about 3 inches high, and assuming I added a new front panel pcb),
=== could be in a range as low as $10.00 (for 100 quantities), especially if I used
=== TWO headers and sockets that were each HALF the size I need for the main
=== board and the front
=== panel board, because then I could just use ONE of each for the two "little" boards.
===
=== (Of course, even $10 is a ∗significant∗ percentage-increase in the total parts cost
=== per unit. But, heck, I can see RIGHT OFF THE BAT that it would save WAY more
===than $10, in assembly labor costs alone (and ∗maybe∗ some in troubleshooting
=== labor, etc, too).
===
=== That would, technically, make it into two busses, I guess. But the "backplane"
=== board would be made so that the "extra" sockets could be added later, for the
=== other card positions, if it ever became necessary, without changing the
=== backplane board's layout.
> 5) card-edge sockets on all the pcbs, with small pcbs that plug into them,
> with discrete wires or ribbon cables soldered to the small pcbs (i.e.
> hand-made custom card-edge-connector cabling, hehehe...),
See above comments about card-edge connectors. This is also much more
labor-intensive assembly and more places for things to go wrong.
=== Yeah. That option was just mentioned "for the sake of completeness".
> 6) pcb-mount terminal blocks with discrete wires, or
<shrug>
Terminal blocks are okay and I'd go that way if I were dealing with wiring
that had to carry nontrivial levels of power (say more than a couple of
hundred mA or so) but for the most part you won't need it. Lots of potential
for error here, too.
=== Yes. The error potential is one of the main possible problems that I see
=== with using any kind of single-wire connections, socketed or not, although
=== if they're socketed/removable, the errors WOULD be much easier to correct,
=== assuming they could be found...
===
=== BUT, there ARE "non-trivial" levels of current, in a few places. The
=== power amplifier board has to be able to push up to 1.5 Amps, through the
=== front panel connectors and on to the device under test (DUT). And the
=== power supply board, obviously, has to supply that juice. In the current design,
=== those high-current signals also pass through the main curve tracer board,
=== so they can have their currents and voltages sensed and fed to the
=== instrumentation amplifiers, etc, that then produce the x-y outputs to the
=== scope display. But, with the new front panel PCB, ∗probably∗ only the
=== sensing-lines will need to go back to the main board.
> 7) something similar to #1, but with some as-yet-unknown (to me) connector
> and/or cabling types (I even considered pcb-mountable modular phone jacks
> and cabling).
Aside from a limited number of conductors these are reasonable, and fairly
cheap. Not terribly robust mechanically, but easy enough to crimp those
connectors on. Unless you need to start crossing wires, etc. They're
probably cheaper than pin connectors, but other than that I don't see that
much of an advantage to going with them.
=== Yes. Easy to crimp. And cheap. Might've been perfect as a cheap, easy
=== source for short 6-wire "jumpers". But, besides being a little "weird" in an
=== application like this one, it turns out that their connectors would just be
=== way too BIG to have any hope of fitting onto the boards, as they are now.
> Which of those (probably out of #1 through #4) sound "good"?
One thing you might consider in terms of using pin connectors is the
possibility of using off-the-shelf cables, such as 34 wires ("IDE cable") or
50 wires ("SCSI cable"), etc.
=== Definitely! See farther below.
> One immediate "problem" I can foresee, with just adding a second side to
> each pcb and then running traces (on the "new" side of each board) to pin
> headers: Our pcb-making process is rudimentary and does NOT include the
> ability to make plated-through holes. SO, to have headers that are
> connected to the new top side traces, while the connectors are also sitting
> on the top sides of the boards, I wouldn't be able to solder the top side's
> trace directly to the headers' pins, since the headers sit right on the
> boards. So I'd have to make an extra row of holes next to each header row,
> that could have pins inserted that could be soldered on both sides. (I was
> thinking I might just use a single-row header, upside down with the longer
> pins halfway into the holes. It might be "ugly". But it would also provide
> handy test-points...).
Test points are good. But you might also consider using a connector that has
way more pins than you need and using a bunch of them for grounds. This is
what's typically the case with a lot of PC internal interconnects, and it
makes for better performance in terms of crosstalk etc. between the wires.
Though I don't know how much of a problem that's likely to be in the
equipment you're talking about.
=== Good point. There ARE some signals for which I'm planning to do that.
> Many of the switches in the unit just happen to use groups of six
> connections. So, for many on-board and board-to-board "jumpers", short
> lengths (six or eight inches max, probably) of 6-conductor ribbon cables
> might be handy, although, changing to double-sided boards might ("should")
> eliminate that need.
Smallest connector you'll probably find is 10 pins, I think, unless you get
the longer strips and cut them, but I'm not sure about the cable connectors.
=== Actually, many/most of the pin headers go down to 2 pins, I think.
> The primary GOAL is still to make the unit easier, faster, and cheaper to
> assemble. SO, I really don't want to use cabling schemes that require a lot
> of time or expensive equipment, to assemble (IDC?). Socketed connections
> are preferred, so that units can be easily disassembled for repairs or
> board-level upgrades. If ribbon cables are used, I would prefer having
> pre-assembled cables available.
See above comment on that. :-)
=== Yup!
> I did buy a couple-hundred new IDE 40-pin cables (with three 2x20 sockets
> each), for $5! And I got several hundred 40-pin breakable gold-plated
> single-row pin headers for about $10. And I got 300 2.5-inch-long 36-wire
> ribbon cables that have 36-pin single-row sockets on both ends, for $30
> including shipping, and 200 36-pin single-row gold-plated headers for about
> $5 or $10. (Actually, I got the ∗300∗ of the new IDE cables, for $5.99 plus
> $21.42 s/h.)
There you go...
=== Ebay can be good for that, as can the military surplus auctions. But I
=== ALWAYS run into TWO HUGE problems, doing it that way: 1) It takes
=== WAY too much time, just to FIND exactly the stuff I need, and even
=== more time to find a large lot that's "a steal". And, 2) It's a nightmare,
=== as far as having a reliable, i.e. repeatable source of supply.
===
=== I've also seen some stuff that looks like it would be PERFECT, that was
=== in fairly large qtys, and was VERY cheap. But it's stuff that I've
=== NEVER seen anywhere else. So I definitely don't want to design it in...
> SO, I may end up cutting the IDE cables so they have just two sockets with
> about 8 inches of cable between them, and using those. Or I may use the
> short 36-pin cables and single-row headers.
>
> However, I am ALREADY running into the problem of ∗possibly∗ not having
> enough ROOM on the new front-panel PCB, for that many large connectors. SO
> I ∗STILL∗ probably need to find something smaller (fewer conductors), for
> the two smaller boards to use, to connect to the front panel PCB, and/or to
> the other boards.
Hm.
> ANOTHER IDEA: If I could find a very large (and very cheap) surplus
> stockpile of ISA "RISER BOARDS" (or even 8-bit passive backplane boards, or
> somesuch) that have 5 or more slots, those could make PERFECT ready-made
> motherboards, to mount in the bottom of the case, with the slots parallel
> to the front panel. Then ALL of my boards could plug into the slots and all
> be connected together, including the front panel. Of course, I could make
> my own similar motherboard-type boards, fairly easily, with available
> card-edge connectors. (But the large, new card-edge-connectors are usually
> quite expensive. Maybe I can find a large surplus lot of them...) But MAYBE
> there's a really low-cost stockpile of something similar, somewhere, which
> would certainly make things MUCH easier and faster and cheaper.
I have a few of those riser cards on hand that I was hoping to find a use for
some time, and you're welcome to those, but I don't know about several
hundred. :-) I had a guy come by with a load of "computer junk" the other
day and declined to take the one Packard Bell machine that he had that was
one of those boxes, probably could've snagged another one, but...
=== Thanks for the offer. I just don't want to "design in" something that I
=== am not certain of having a large, fairly-reliable supply of. I could probably
=== very-easily buy a few thousand identical PCs, from a military
=== surplus auction or two, probably for about $1000 to $1500 for each semi
=== trailer load, which is what I used to see them go for, all the time. But,
=== just having to go through the buying and transporting and storing and
=== removing what I wanted and disposing of the rest would almost certainly
=== make it uneconomical, not to mention "WAY too much work". (It might
=== be different if I could find a decent way to use the whole case, and the
=== power supply, AND the motherboard slots, ALL left INTACT, where I
=== could just plug in my boards and mount my front panel stuff
=== somewhere... Hmm.... Whacky. But maybe for some other product!)
> There are also several connections to the rear panel, usually with only one
> or two wires, that I need to worry about. I am thinking of using either
> one- and two-wire pin headers and sockets, for those, or small terminal
> blocks of some type. However, I still would LIKE to have all pre-assembled
> cables (i.e. sockets already on both ends of appropriate-length cabling.
For something like that I've seen some commercial gear that used different
styles of connectors (all 2-pin) so you couldn't mix them up and plug
something into the wrong place. You could also handle that issue by setting
the wire length to be only appropriate for where it's supposed to go and
similar tricks. Something to worry about, anyway.
=== Another very good idea. Noted!
> Peak currents in some of the signal conductors could reach 1.5 Amps.
> However, most of those waveforms are triangular or sawtooth, making the
> average (DC-equivalent) current only HALF of the peak value. But the main
> DC power supply rails MAY have to be connected from the separate power
> supply board to the other boards using discrete wiring that's screwed into
> terminal blocks, for that reason (max current-carrying capability).
Or at least something that's heavier-duty than pin connectors, though it's of
course possible to use several of those pins for this purpose.
=== Even the low-cost pin headers from jameco.com are rated at 1 amp per
=== pin. In this case, the 1.5 amps is the PEAK. But it's for ramp-type
=== waveforms. So the average "DC-equivalent" current would only be HALF
=== of the 1.5 Amps. And yes, the power supply rails (and grounds) for
=== each board were going to be kept separate, anyway. And, as you said,
=== I could always run them doubled (or more), for any high-current ones.
The Osborne 1 computer had a weird custom board on their floppy drives, which
was A and which was B was determined only by where the terminator position.
This was before twists in cables and similar nonsense. They also ran the
power for those drives up through the ribbon cable, to a card-edge
connector. There were reliability problems with those over time...
=== Is it possible that the newer card-edge connectors are better, now?
=== Well, never mind. Wherever I would have wanted to use card-edge, I
=== can use pin headers and sockets, instead.
> Sorry to have blathered-on for so long, here! If there's anything you can
> offer, I'm all ears!
Hopefully some of what I've kicked out here will be of some help. I see a
lot of different things being done in commercial gear manufactured over a
long period of time, from no connectors at all to a bunch of different
alternatives.
=== YES. ∗∗QUITE∗∗ helpful. Some great ideas, and stored wisdom! And
=== usually it also helps just to hash through it, with someone else, anyway.
===
=== I DEEPLY appreciate your taking the time and energy to respond,
=== so well, and your willingness to share your knowledge and experience.
If I were building something I think I'd probably tend to favor pin connectors
for signals and something a little heavier for handling any kind of power,
maybe a "pin connector" that's larger (0.156 spacing?) and that uses the
square pins for a better contact.
===
=== Sounds right. I might even use the PC disk-drive-type power cables,
=== for the heavier stuff. (I just missed a chance to get a lot of something like
=== 500 brand new "Y"/splitter PC disk-drive power supply cables, on ebay,
=== that went for something like $10, total...! Those could have connected
=== all three of the boards... :-o )
===
=== Thanks again, ∗so∗ much! You, and the others on this wonderful group,
=== are truly great. If there's EVER anything that ∗I∗ can do, to help (any
=== of) YOU, please, just ASK!!
===
=== Highest regards,
===
=== Tom
===
=== Thomas P. (Tom) Gootee
=== tomg(AT)fullnet.com
=== http://www.fullnet.com/u/tomg
=== Jasper, Indiana, USA
===
===-------------------------------------
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