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Next steps in the Arduino Concertina.
As near as I can tell, what I need for the electronics portion of the Concertina at this point is about 30 more buttons, about 50 diodes, and a lot of soldering and connecting. (I am excluding such piffling details like a power supply and an amp/speakers).

The buttons I'm using are marked R13-24, and appear to be R13-24A-05-BB and -BR buttons. They appear to cost about $1.25 each, so all told there will be over $60 worth of buttons in this thing, probably the most expensive component. That is, if I can find a good seller. I believe I got these at Radio Shack originally, but they don't appear to be in the catalog anymore. They aren't carried by Jameco or Digikey either. Google Shopping lists Newark.com as a seller (that's where I got the $1.25 price), but I know nothing about them. Anyone have any other suggestions for possible suppliers?

For that matter, I seem to have misplaced the M7x0.75 panel nuts that came with the switches I have, and can find nothing about them online. Any thoughts there?

The R13-24 buttons seem to be the perfect size for this application. The button caps come in red and black (the -BR and -BB variants) and are 6mm in diameter. This seems to be about the same size as the buttons on a real concertina. It mounts via 7.2mm holes, the threads are about 5-6mm long, so even after going through a 3mm board there's still plenty of room for the panel nut. The flange has the same diameter as the flats of the nuts, and is the widest part of the switch. Since the spacing of the buttons is 0.4" by 0.5", they will fit with about 3mm between the holes -- tight, but doable. Bigger switches wouldn't fit, and smaller switches with the same button size are even harder to find.

What I need for the case is to redo the artwork for them. Somehow I managed to lose the original CAD drawings. The basic shape for the end-panels are hexagons, about 7" corner-to-corner, with holes for the buttons in the middle. The edges should also have slots cut to join to the side panels. The side panels are essentially rectangles with tabs cut on both ends to mount to the end panels.

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Wow, buttons are expensive :)

Would it be overkill to suggest making you own with a PCB, those black contact buttons on the back of the rubber keyboards, and dowels or mass produced buttons. I was thinking about this when I wanted to hack the steering wheel on my car.

Even casting resin might be cheaper.

It might be cheaper to do it that way for a large run, but the production costs for one-off PCBs are high. Effectively, I have 12 rows of buttons on 0.2" centers (I have 6 rows on 0.4" centers, but half of each row is offset by half a row-spacing), and 4 columns on 0.5" centers, so the board will have to be at least 2.5"x2". I would also have to have 2 board designs, since the left and right hands are not identical. That's 10 square inches, minimum. OSH Park, a typical highly regarded prototyping service, will do the boards at $5/sq.in., and give me 3 copies. If the left and right sides identical (as opposed to near-mirror-images), it'd be a great deal for this. As such, it's barely competitive with the switches.

The switches themselves are just about perfect for the task. The size of the buttons and the throw of the buttons is very similar to that of the actual concertina. It's just a shame they are so expensive.

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