Homebrew PCBs

Tom,

Go to the Geckodrive yahoo group and have a look at the pictures in 
their file section. You can see what a "pin based" MB and cards setup 
looks like... (You may have to join the list to view the 
files/photos, but it'll be worth it, IMO.)

Hope this helps,

Ballendo 

--- In Homebrew_PCBs@yahoogroups.com, "Thomas P. Gootee" <tomg@f...> 
wrote:
> === 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@b...>
> 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
> ===
> ===-------------------------------------
> 
> 
> 
> [Non-text portions of this message have been removed]