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Wednesday, October 6, 2010

Build a simple switch - Hack a Day

Build a simple switch

posted Oct 5th 2010 2:00pm by Mike Szczys
filed under: peripherals hacks

Forget hacking an easy button, grab a couple of those outdated CD-Rs and build your own switch for that next project. This was developed with handicapped accessibility in mind; assembled easily with common products and it’s fairly robust. In fact, our junk box has everything you need except the adhesive backed copper foil. Combine two old CD’s, covered in copper on facing sides, separated by two strips of Velcro to separate the conductors. When pressure is applied, one CD flexes to make contact with the other and complete the circuit. So easy, yet we never thought of it. We’ll add it to our list of homebrew input devices.

[Thanks Michael]

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CD Switch

IntroCD Switch

In the realm of assistive technology, a switch (aka "ability switch") can be anything from a plastic button to a muscle twitch sensor.  This album is a great look at the variety of switches that are available.  These switches are almost always wired to a 3.5mm (1/8") mono plug, and can be connected to anything with a matching jack. They are used with power wheelchairs, computers, speech devices, toys, remote controls, and so on.

The problem is that switches are expensive.  A basic Jellybean Switch or Buddy Button costs around $50-60 (USD), for just a plastic button.  While these are worth their weight in gold, the price is still a bit steep, especially in the low-budget/non-profit world of assistive technology.

Sometimes, it's handy to make your own.

Fortunately, a switch is a very simple thing.  It's just a circuit closing, just two wires touching.  We will use less than $10 (USD) worth of parts to let a person press a surface (in this case a CD), and touch two wires together.  R. J. Cooper also sells CD Switch Kits for about $10 (USD) each, in packs of five or ten.

Save the left over scraps from this project, as you can use them to build a No-Solder Battery Interrupter , which you can use to let this switch control toys and other devices.

Step 1

Materials Needed:

Adhesive backed copper foil sheet .  5"x10".
Adhesive backed Velcro strip .  6" of each side.  
(I used 3/4", but nearly any width should work.  Foam mounting squares will also work.)
- 3.5mm mono cable with male jack.
(Buy a 3.5mm mono extension cable , cut it in half, and use the male end for this, and the female end to make a No-Solder Battery Interrupter .)
- CDs.  2.
(Old software, AOL trials, blanks, whatever you have laying around.)


- Scissors
- Ruler
- Sharpie (or other fine point marker)


In steps 2-4, I would do things a little differently my self. Instead of cutting out Circles and trying to then match them back to the CD's most likely ending up with miss matched pieces that are permanently stuck in place... If you've ever worked with Decals or Sticky Tape. You know how hard exact placement of something sticky and the object you want to stick it too can be! This should save you some time and frustration... I would just sit the CD's on the Sticky Foil to mark out squares slightly bigger than the CD's. Then cut out the Squares. Then, Peel the Backing off the Sticky Foil, with the Sticky Side up on your Work Bench - Table, what ever you have that it flat. Then just lay the CD's down on the Sticky Foil. Then flip them over and trim the Excess Foil with a Box Cutter or ExactO Knife, something with a thin sharp blade. Don't to this on your Wife or Mothers Kitchen Counter Top!:O She will whip your Butt if you do! And never let you forget how you completely ruined her Kitchen Counter Top! You've been warned!...;) You can use a flexible, straight edged plastic Squeegee to push the Air Bubbles out to the edge of the CD's, to get rid of them. Now a Days, I just use the ones that came in Some Auto Body Bondo that I bought a few years ago ( I keep them clean enough to reuse). They sell them all over for putting on Decals though. You can also use your fingers and thumb to Push the Air Bubbles to the Edges of the CD and eliminate them that way. An old trick for putting on Decals may help here. But, I'm not sure just how sticky the Sticky Foil is, since I've never actually worked with it. But, you may be able to use a wet sponge, dipped in water, squeezed out so that it does not drip, just leave it damp. Before you stick the CD's down on the Sticky Foil, just swipe them lightly withe the Wet Sponge. This will make it allot easier to wipe out the Air Bubbles after you stick them onto the Sticky Foil. I would just try one first and see how well this works, before doing them all this way...
Ok, now you're ready to finish building your CD Switch and you didn't mess up any of your Foil and end up with stuck together forever pieces, good for nothing but the trash;)


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