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As far as I know, this is the first of its kind.  A physical button that plugs in to any smartphone through the headphone jack.  You are probably asking yourself, why would I need this!?  Smartphones already have buttons on the screen.

For children with physical disabilities, using a smartphone is almost impossible.  However, they can really gain access to the amazing capabilities of a smartphone with a simple button.  For example, see my adaptation for controlling Sphero with a tilt of your head.

This instructable will go over where to buy the button, create the adapter, and use the software to take advantage of this assistive technology.

Note:  This adaptation will only work for an Android phone with a microphone line-in.

Step 1: Bill of Materials

The project will require several components and tools.

Components:

1) Assistive Button  $35

OR

1) Assistive Buttons  $10

2) Female Mono/Stereo Audio Jack 1/8"   $3.19

3) Male 4 Conductor TRRS Audio Plug 1/8"  $6

4) 4 wires, No Matter Length $0-$10

5) 100-100k ohm resitor $1 (RadioShack)

Tools:

1) Solder
2) Soldering Iron

How to Save Money:

The second link for the assistive button is much cheaper.  The first link is simply the top of the line, very durable and sensitive button, perfect for children with complex disabilities.  Hence, why it is so expensive.  A simple CD switch will suffice as well. 

Also, you can use any wire you have around the house.  Just make sure the gauge is small enough to solder to a small audio jack.  And you can use any size resistor, it just needs to limit the current for the microphone.

Borrow a soldering iron and solder from a friend.

Step 2: Assembly

If you have ever soldered before, you are a leg up on this step of the project.  If not, you are attempting to solder one of the harder components in electronics... the audio connector.  So, it would be helpful to have an experienced assistant on hand.

The schematic for the adapter is shown in the figures attached to this step.  VR is the right channel audio wire, and WL is the left channel.  R is the resistor.  Vsw(+) is the input to the button (sleeve) and Vsw(-) is the output, or tip.  These are all shown in the figures attached to this step.

If you cannot read a schematic well, the pictures with the colored wires may help!  Black is ground, white is microphone, grey is right channel, and purple is left channel. 

After everything is soldered together, I used a hot glue gun to strengthen the connection.  Also, I put electrical tape over the exposed wires for a better look.  I chose electrical tape instead of shrink wrap to be able to trouble shoot better.

Step 3: Software Test

Download the APK file attached to this step to your phone and plug in the button you have made.  Turn up your volume to 100%.  The number is the sound energy of the microphone input.  You should see a spike in that number and the screen should turn blue when you click the button.  If this happens, you have successfully created the button!

If not, here are some trouble shooting tips:

1) Make sure your Android phone has no media audio effects on.  Go to Settings -> Sound -> Media Audio Effects -> Wired Connection -> Disable Audio Effects.

2) You actually have a microphone line in to your phone

3) Media Volume is 100%

Post a comment if you cannot get it working, and I'll see if I can help.

Good luck!
<p>Can you explain how this works?</p><p>is it the same as the Android buttons that are currently on sale?</p><p>Thanks.</p>
<p>great idea, can you adapt the Apa to be usted with a game? Taje pictures with the camera app? Control Music? I world like a los cost solution. For People with Disabilities in Colombia</p>
This is top shelf.

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