[sdiy] Substitute for pin matrixes?

[ASSI]

On Sunday 24 January 2010, karl dalen wrote:
> >Is it much of a problem that you occasionally may have to pull a
> >pin and re-seat it?  Yes, I think I'd get several years of
> >lifetime out of it, YMMV.
> 
> Now i tested on a turned socket, about 70 inouts it had wear'ed off
> the resistor legs plating  this clogged up the spring, it still
> worked but its very stiff to insert and unplug, after 120 it was
> even worser still working after 150 leg got stuck, probably the
> spring that gave in.

I said on the outset that the leaf type contacts would work better for 
this and my comments were directed to those.  The turned pins are 
designed for only a few matings cycles with very good retention, your 
result confirms that.

I don't know how the solderless breadboards are speced, but I have yet 
to wear one out (except if I try and force square pegs from PCB pin 
strips into them, that will kill that contact right away or at least 
make it unuseable with anything other than square pegs).  I've seen 
the contact strips from those boards on a surplus sale somewhere a few 
years ago, don't know if you can still get them.

For much better contacts, check this out: http://www.hypertac.com
Their test system connectors are something to marvel over.  Certainly 
not cheap, but they give you 30,000 mating cycles.  More interesting 
should be the stamped contacts that might provide a venue to get 
matrix receptables with a decent number of mating cycles at bearable 
cost.

Card edge connectors might be another idea as they have two 
independent contacts facing each other.  The mechanics of the "pins" 
are somewhat questionable if you want to operate them independently as 
you would have to rely on the coding slots to provide retention.  
You'd need a T-shape plug with contacts on either side of the vertical 
bar of the T if you use all contacts (probably impractical) or a H 
shaped plug with the contacts either side of the horizontal bar to use 
every third contact.  If you just want patch storage and operate all 
contacts at once, this is a tried solution (Buchla and EMS did this 
and have been mentioned already).

Oh, and reeds might not be such a bad idea after all if you operate 
them with moving permanent magnets via a push-push mechanism (like a 
biro).  Or just use 100 actual biros from some office supply sale and 
have them push on a matrix of micro switches.

Going back a century or so (nothing wrong with that!) you could pull a 
Hollerith and use an array of pogo-pins and a cardboard with holes 
where you want a connection and no holes where you don't.  If you're 
old enough, you might still know this as a punch card.  Combined with 
todays SMT you might even be able to provide multiple resistances per 
matrix point if you can get the holes punched precisely enough.


Achim.
-- 
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