Intro: 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
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
TOOLS AND MATERIALS
• 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
• 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
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
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
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
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
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
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
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.