[sdiy] Substitute for pin matrixes?

[Jerry Gray-Eskue]

The only tricky thing to this scheme is the split pad with plated through
holes, The problem is the through hole plating will short the split pad.
I see two possible solutions.

(1) set up the split pad as a standard plated through hole and after receipt
of the fabricated board cut a slot on each side at the split point clearing
the plated through short. - at additional fab cost you may be able to get a
board house to do the post slot cuts.
(2) use a secondary via to connect to the bottom side and specify the split
pads as non plated through.

Of these the plated through version would make a more reliable connection as
the ball will only touch the very edge of the hole.
Additionally if you use light weight balls you may be able to use a flat
sheet of magnetic material on the bottom side of the board with magnetic
balls to keep them in place and provide some additional contact pressure.

An additional consideration would be using silver plating for the best
connection (lowest resistance), or gold plating for the best oxidation
resistance and
reasonably low resistance.

- Jerry




-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of John Mahoney
Sent: Sunday, January 24, 2010 10:36 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Substitute for pin matrixes?


At 09:51 PM 1/24/2010, Tony Clark wrote:

>Maybe I'm not quite envisioning this correctly, but you can simplify
>this down to just a single layer of PCB with a hole (smaller than the
>size of the ball)  that has two plated half-rings around the edge.
>When you drop your ball in, it will connect the one half to the other.

That's like what I was trying to describe in one of my magnet-related
schemes -- pads made of 2 half circles. I don't see how you can do a
row/column matrix with a single-sided PCB, though, which is why I
spec'd a double-sided board. One of us isn't envisioning it
correctly, for sure. <G>

That's when I remembered Nic Collins' writings on the use of computer
keyboards, which are the cheapest switch matrices that I can think
of. (No comment on that one, Karl?)

As cool as the ball bearings would look, I wonder if they would make
for reliable contacts. Also, they could easily be knocked out of
position, which provides some unusual performance possibilities but
isn't the kind of UI that I'm looking for. That's why I suggested
magnets -- personal bias at work.

John

_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy