Introduction: Foil Capability Switch

Picture of Foil Capability Switch

In Assistive Technology, one of the major areas that is considered for people with significant disabilities is switch access.  Using a capability switch or accessibility switch, someone can control their environment, play with a toy, use a computer, or communicate.  All manner of switches are available commercially - switches that work on mouth pressure, fingers, muscle twitching, pulling, pushing, etc.

The problem is that special needs are - by definition - special.  You do not have to work in this field long before you encounter a client whose needs can not be met by an existing product. 

The foil switch allows for rapid customization of switch access.  It allows for prototyping abilities not found in commercial products.  The therapist can quickly (in the field) evaluate many different sites for switch access and experiment with various ranges of motion.  It also means that a therapist can make a switch custom-tailored to an individual.   The user can become the switch.

The foil switch activates with an extremely light touch, which is great for clients with low muscle tone.  It is also very cheap to make - it costs about $1 for a switch (some commercial switches cost hundreds, but most are under $100 USD).   It follows a "make once, use many" approach - once the wiring harness is made, it can be reused again and again and be instantly customized by changing the shape of the aluminum foil.

Over the years, it has proven itself to be an extremely versatile tool and we have used it with many clients, both adults and children.

Step 1: History

Picture of History


We developed this switch when working with a little boy who had Spinal Muscular Atrophy (SMA). The only movement he could make was moving one finger about 3-5 mm. He had practically no muscle tone at all. He normally laid on his side and used a ventilator to help him breathe. We tried all the commercial switches we had (a sizable amount), but he couldn't  use any of them. The membrane switches (very light pressure required) were unusable because he couldn't generate enough pressure to use them. Some of the other switches, such as the beam breakers, worked but hampered his breathing because they rested on his ribcage (he had no intercostal muscle control), so they couldn't be used because of the difficulty in mounting them and the interference with his breathing. He was able to use the aluminum foil switch easily to turn toys on and off. It was fantastically light, activated with bare amounts of pressure, molded its shape to his chest, did not impair breathing, and succeeded where $600 switches had failed in the previous evaluation.

Step 2: Tools and Materials

Picture of Tools and Materials

TOOLS AND MATERIALS

Tools

• Scissors or knife
• Wire strippers
• Soldering iron
(you can just use electrical tape, but it will be weaker)
• Heat gun (hot air gun) or very hot hairdryer

Materials

• Alligator clip leads. Longer lengths are better. Each clip lead makes one switch.

Radio Shack #: 278-001 $6.99 / 4
BGMicro.com #: CAB2157 $2.56 / 10

• Male 1/8” to male 1/8” mono cable. One cable will make two switches.

AllElectronics.com #: CB-3510 $1.50

Radio Shack #: 42-2420 $4.99

• Solder (e.g 60/40 0.062” diameter rosin-core)
• 1/8" diameter heat shrink tubing (electronics store)
• Electrical tape (optional, if not using solder)
• Heavy-Duty Aluminum foil (grocery store)
• Solid Foam shelf liner (grocery/hardware store)
• Spray adhesive (optional, hardware store)

Step 3: Make the Base Plate

Picture of Make the Base Plate

This step can be customized in a number of ways.  These instructions are to make a very generic pad, but this is adjustable based on individual needs.  In some cases (as seen later) this step is not even needed.

In this case, I have made a 5" square template from cardboard.  I use it to cut a matching shape out of the foam shelf liner.

Cut a square of aluminum foil about 2" bigger in both directions than the shelf liner piece.

Spray the aluminum foil with spray adhesive on one side only.

Place the foam shelf liner in the middle of the foil.   Wrap the sticky foil around the edges.  Aluminum foil can be pointy at 90° bends (this is why the corners are rounded).

In this case, the foam shelf liner provides three functions:

1) It acts as a non-skid backing, thus making it easier to keep in one place
2) It helps the foil pad conform to shape
3) It gives additional strength and support that would otherwise be lacking.

Step 4: Make the Wiring Harness

Picture of Make the Wiring Harness

Cut a clip lead in half.  Strip 1/4" of insulation from each cut end.  Twist inner wires together.

Cut an audio cable in half.  One audio cable makes two switches, so ignore one half unless you are making two.
Strip 1" of insulation from a cut end.   Twist the loose wires together to make a big wire (barrel conductor).  Strip 1/4" from the inner wire and twist the inner wires together.

If you are using a stereo cable instead of monoaural, you will have two inner cables.  Use a multimeter to tell which is ring, tip, and barrel conductors.  The ring and barrel conductors can be twisted together to make a monoaural cable.

Slide 1" of heat-shrink tubing over each clip lead and push it a ways up the wire.  Slide 2" of heat-shrink tubing over the audio cable and push it up a ways.

Solder a clip lead wire to the tip conductor wire.  Solder the other clip lead wire to the barrel conductor.

Push the heat shrink tubing on the clip leads over the exposed solder joints.  Use  a hot air gun to shrink the tubing and lock it in place.  This prevents electrical shorts and adds stability.  You could also wrap the joints with electrical tape.

Push the heat shrink tubing on the audio cable over the shrink wrap of the clip  leads.  Heat with the hot air gun to lock in place.

You should have an audio cable that splits into two alligator clip leads.  I call this the wiring harness.

Step 5: Using the Foil Switch

Picture of Using the Foil Switch


Clip one alligator lead onto the base pad, making sure it contacts the aluminum foil.

Clip the other lead onto a thin strip of aluminum foil that is wrapped around the user's finger.

Plug the audio end into a switch-adapted device.

The switch is closed when the user touches the two pieces of foil together.

The switch is open when the user separates the two again.

Step 6: Other Uses - Car Switch

Picture of Other Uses - Car Switch

A switch should be a means to an activity, not the activity itself.  Still, for some children an additional motivator is needed for them to interact with the switch in the first place.   This is an example of a motivating switch, the "car switch".

This took me all of five minutes to make, with four and half of those waiting for the hot glue gun to get hot.

Cut two pieces of cardboard (3"x5" or so).  Wrap each piece in foil.

Put a dollop of hot glue in the middle of one piece.

Cut a piece of foam smaller than one of the cardboard pieces.  Press it into the foam.  Cover the top of the foam with hot glue.  Press the other piece of cardboard on top.  Imagine it is a sandwich - the foam is the meat, glue is the condiments, foil-wrapped cardboard is the bread.

Hot-glue a car to the top piece of cardboard.

Attach one clip lead to the top piece of cardboard.  Attach the other clip lead to the bottom.

When the child presses the car, the switch will rock, the foil will touch, the circuit is closed.
When the child releases, the foam pushes the foil apart and the switch is opened.


Step 7: Other Uses - Glove Switch

Picture of Other Uses - Glove Switch

This is useful for someone who can open/close a fist but has difficulty with other movements.

We took a glove that would fit the client.  He seemed to use his two middle fingers in tandem.  We hot-glued a strip of foil to the palm of the hand (not while the client was wearing the glove - very important).  We hot-glued another piece of foil around those two fingers and bent the foil so it formed a striker. 

One clip lead is connected to each piece of foil.  To close the switch, the client touches the two middle fingers to his palm, (like Spider-man's web shooter or "hook-em-horns").

Relaxing the hand automatically breaks the circuit.

Step 8: Other Uses - CD Switch

Picture of Other Uses - CD Switch

For this, take a CD case, a small piece of packing foam, and two strips of aluminum foil.

Glue the foam in the middle of the CD case.  This will push the two sides apart when not being used, keeping the circuit open.  The size, shape, and position of the foam determines how easy this switch is to close. 

Glue a piece of foil to the top edge.  Repeat for the bottom edge.  Make sure the pieces don't normally touch, but will if pressure is applied to the CD case.

Attach a clip lead to each piece of foil.  Press the CD case to close the circuit.  Release the CD case to open it again.

Step 9: Other Uses - Foot Switch

Picture of Other Uses - Foot Switch

We worked with a six-month old who had arthroglyposis.  She could not move her arms but she could move her legs.  So that she could play with adapted toys, we did several things for her.

First, we made a pad (as in the main instructable).  Next, we covered one of her little shoes with hot glue and then covered it in foil.  One clip goes to the pad, the other to the shoe.  She could activate toys by kicking her foot against the plate.

We also took her soft socks / baby booties and sewed the loop side of a piece of velcro to the sock.  We hot-glued the hook side of velcro to a strip of aluminum foil that had been folded over a couple of times.  This made a wide variety of adjustments possible, and allowed us to experiment with a lot of different configurations.

Comments

swildman (author)2013-08-16

I have a very different comment. I think it AMAZING what you do for these people. I always feel so bad for people with disabilities that can't express what they are feeling or thinking or what they desire. You give them a voice! I think that's amazing!!! Thank you!

Heybye44PTX (author)swildman2014-06-15

I feel the same way too. My brother is autistic, but he is learning.

Dylon124 (author)2013-08-28

what is this supposed to do? Just use an arduino

shadowwynd (author)Dylon1242013-08-28

This allows someone with limited movement to turn something off or on. It is just a switch. By itself - it does nothing. Paired with the right technology, it allows someone with very weak muscles to communicate, to use a computer, to change channels on a TV, to play with a toy, or use ....... whatever (including, I suppose, an Arduino). The advantage is it is incredibly cheap and incredibly versatile. There are many switches on the market that cost $$ or $$$ and do not work as well as this for certain people.

silvaticus (author)2013-08-21

Thank you for this! I work at an ICF-MR. Customization balanced with cost is always an issue. I will using this!

billbillt (author)2013-08-17

great work

Kiteman (author)2013-08-16

Since you wrote this, conductive thread and paint have become more widespread - have you thought of incorporating those in your custom switches?

shadowwynd (author)Kiteman2013-08-16

I have tried conductive thread a couple times. It works for some people and some instances. We tried conductive thread with a glove (touch fingers together, etc.). The aluminum foil worked better in that case.

I haven't used conductive paint yet. I have tried using graphite (pencil lead) on some things before with mixed results.

Kiteman (author)shadowwynd2013-08-16

Thanks!

RooMooJoo (author)2013-06-12

Great idea! I was using micro-switches, which can't always be put to purpose in certain situations.

juiceman74 (author)2011-10-09

I had my 6 graders make games and type writer application with similar switches.  We used Picoboards (I bought individual boards for $70).
10x for the great contribution.

BTW - do you have an idea how to make a spindle switch that turns on with centrifugal force?

spark master (author)juiceman742012-06-17

use a top that light up?

juiceman74 (author)spark master2012-06-18

what kind of top? I didn't understand you.

Thanks for the reply.

spark master (author)juiceman742012-06-18

kids toy that lights up on spinning similar to or a duplication of a tilt switch. ballbearing is in a slide as it spins the force pushes the ball bearing into the end (cup) and it shorts the edges ligting up the top.

you could do same I guess.

short plastic tube seal one end at switched end embed two (or six every other one is half th eswitch , so no matter how the ball goes in it works) wires either side of tube mounted at upward angle , as it spins ball moves up shorts the leads, like a mercury switch.OR Use two pieces of printed circuit board in shape of a Vee at the action end and it should work quite nicely

If it has to work in any position while spinning it must be spring loaded so the ball can move freely ONLY when spun.

Duncan used to make tops that lit only when spinning , if the top has an on off switch and is not spin activated the switch won't work. Those switch quite a bit of rotational speed to function.

sHADOWWYND 'S CONCEPT OF ARMS THAT FLY OUT AND MAKE CONTACT IS BETTER , SINCE YOU NEED A MORE INVOLDED SYSTEM TO GET THE SWITCH FROM INSIDE A SPINNING OBJECT TO DO SOMETHING OUTSIDE THE ROTATING BODY. iT CAN BE DONE , JUST NOT EASILY

shadowwynd (author)juiceman742011-10-09

I assume (you could do it the opposite way also) when stopped, no contact between conductors.  When rotating with enough force, contact is made between conductors.

My first thought would be to look at a couple technologies:

Tilt Sensor (anti cheating) for pinball machines
http://electronics.howstuffworks.com/pinball-machine4.htm

Steam flyball governor
http://www.history.rochester.edu/steam/thurston/1878/chapter3.html

In the first, gravity normally separates the contacts when the machine is upright, contact is made when tilted.  In the second, the governor is placed on a rotating shaft.  The balls get further apart the faster the shaft goes. 

If the direction of shaft rotation is perpendicular to gravity, a couple options come to mind.

First, you could make the pinball tilt sensor, but connect the plumb bob to a vertical rotating shaft with a spring.  Use a slip ring to transmit electricity to a collar that is soldered to the spring.The spring will be partially mounted on the vertical shaft.  When the shaft is stopped, the spring will hang straight down due to gravity.  When the shaft is in motion, the weight will move sideways, the spring will bend sideways, the spring will contact the ring, thus closing the circuit.

You could also make something similar on the edge of a flywheel.  A contact spring bends outwards when the wheel is spinning and touches a contact plate, then returns to an upright position when stopped.

If you can find a glass-tube mercury tilt switch (from old A/C control units, etc.) that would make an easy tilt switch also.

You could have a weight (non-conductive) attached to a spring in a tube or track.  When the rotation is stopped, the weight is near the center.  When rotating, the weight slides down the track and presses a button (commercial switch).

You could have a piece of metal in a nonconductive track, attached with a spring to the center of the rotating object.  When there is no rotation, the spring keeps the metal near the center.  When rotating, the metal slides down the track and bridges two contacts, OR the metal weight is electrified and thus is the other contact.

These would also work if you had a horizontal rotating shaft, but you would need to make sure the spring is stiff enough that it does not touch due to gravity, only rotation.

juiceman74 (author)shadowwynd2012-06-18

Shadowynd, Thanks for the interesting ideas.

I'm in the direction of the more simpler suggestions you gave. In the attached picture I've drawn my idea. I still need to check it out.

Kid's toys use a spring that bends with force with spin and creates contact with another meta which short circuit.
What is the idea behind the horizontal rotation shaft?


spark master (author)2012-06-17

glue conductive foam to a non conductive glove, then hook a wire to each finger, if you use resistors in series with each finger and all are different you could make a circuit that does yes/no maybe, or on off up down etc. If the client can use the fingers you got it all 4 in parallel gives a fifth ohm rating and the "reciever" can dope them out, and activate different things.

if you like complete digital use a source for 4 different square freqs and a reciever to see them , and outputted to various devices.

foobear (author)2011-07-31

very interesting

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