Homebrew PCBs

Just a couple more comments...

On Sunday 22 August 2004 10:04 am, Thomas P. Gootee wrote:

> > 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!

This would also probably involve making a "harness" for the wiring,  which may 
make things a bit more labor-intensive,  and may also prove to be a 
disadvantage when it comes to bundling stuff together that really shouldn't 
be.  I can't speak more to that without knowing more about what sort of 
signals are running around in that equipment...

<...>

> 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?

No doubt they are,  at least once things progressed beyond ISA slots.  I have 
heard of some ISA connectors giving trouble,  and even encountered that 
*once* that I can recall (one of my XT-class MBs has a bit of black tape over 
one slot :-),  but have never heard of this being the case with PCI and AGP 
slots,  which use a different style of connector and a lot more pins.

<...>

> > 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 )

Now *those* have had their share of problems too.  Like the common Molex 
connectors,  reliability leaves something to be desired when you're looking 
at a female contact which consists of a bit of sheet metal that's going 
around a pin,  I don't know if this is a matter of what material is used for 
the contact or not.  There have been a few instances where I've had to take a 
small tool of some sort and close them up a bit,  after they'd opened up 
some...

The same is going to be true to some extent for DB-xx connectors,  though 
they're better at it as the positioning and size of the male pins seems to be 
more tightly controlled.

My preference for high reliability is contacts that have a "wiping" action, 
which can be seen in the "Centronics" style connectors used on the back of a 
printer,  which I've also seen in sizes of 24 and 50 pins and there are 
probably others.  Some "external" connections on SCSI cards seem to offer a 
miniature version of this,  like on my Adaptec 2940uw,  and the SCSI-wide 
connector is similar in a 68-pin version as well.  Some of the pin connectors 
I've seen/used over the years are based on a similar idea,  though I don't 
have part numbers handy.  The one half is a square pin (though sometimes 
round ones are used too),  and the other half is a bit of sheet metal that's 
"folded" several times (think of an "@" character :-) and has some continuous 
spring pressure holding it up against the other half.  This is in sharp 
contrast to a bit of sheet metal that's supposed to wrap itself around a pin.