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Switches are essential to designing interactive wearable electronics. You will learn all about them in this lesson and make your own out of conductive fabric, thread, and snaps!


You will learn:

+ common terms when talking about switches

+ how to design a switch

+ how to make a switch from sewing notions

+ the basting stitch


Materials

Download the attached file for the snap switch pattern.

+ conductive thread

+ conductive fabric

+ hand needle

+ regular thread

+ felt

+ alligator leads

+ multimeter

+ fabric pen

+ scissors

+ 1 x snap set (one post and one socket)


Hi-5 Collector Project

From here on out, everything you learn will be put towards the final project, the Hi-5 Collector. This is designed to be a fun project meant to get you out and interacting with people. This project can be made for almost anyone and captures the basic principles of building and designing wearable electronics.


What Is a Switch?

A switch is a mechanical device that can be pushed or pulled to open and close in a circuit, allowing electricity to flow or not. Once the electricity flows, this can trigger events, like turning on an LED or supplying power to a fan. You can also read whether a switch is open or closed when it's hooked up to a microcontroller, which we will get to in a later lesson.

The above diagram is the same basic circuit from the Introduction to Electricity lesson. Accept now a switch has been added. I've used the schematic symbol for a single-pole, single-throw (SPST) switch, which is the most basic kind of switch. A SPST (single-pole, single-throw) switch has two contacts. This pair of contacts can be in one of two states:

1) Open, meaning they are not touching, not allowing electricity to flow

2) Closed, meaning they are touching, allowing electricity to flow.


Kinds of Switches

There are two main categories of mechanical switches.

Momentary

A switch that is designed to be closed or open momentarily. For example, while pressed, it's closed, but when released it becomes open.

Maintained
A switch that holds one state (open or closed) until it's interacted with again. Like a household light switch, you flick it up, it stays on, flick it down and it stays off.


Different kinds of switches:

Pushbutton
When a switch needs to be interacted with by pressing or pushing, it's a pushbutton. This kind of switch can be momentary or maintained.

Toggle
Toggle switches are maintaining switched. They are interacted with through the use of a lever, rocker or handle. The most common example of a toggle switch is the household light switch.

Rotary
Rotary switches are used by twisting a knob or dial to indicate position. Some come with two positions, some can go up to 10. They can include momentary and maintained positions.


Through research, you will find there are many different kinds of switches. Ones that can be engaged through many types of elements and physical activities, such as tilting, the turning of a key, liquid levels and magnetism.


Poles and Throws

Poles and throws also help to define different kinds of mechanical switches.
In this lesson you will build two switches:

1 x single-pole, single-throw, maintainingswitch
1 x single-pole, single-throw, momentaryswitch

Momentary and maintaining have already been defined, so we will focus on the other terms being introduced.

What does "pole" and "throw" mean?

The pole refers to the number of separate circuits that the switch can control. A single-pole switch controls just one circuit. A double-pole switch controls two separate circuits.

The number of throws indicates how many different output connections each pole can connect its input to. Read the switch symbol left-to-right, putting the output on the right. A single-pole, single-throw switch has one input able to connect to one output. A single-pole, double-throw has one input able to connect to two outputs.

The diagrams above and below show the two different states that four different pole and throw configurations can have.

Single-pole, Double-throw

Double-pole, Single-throw

Double-pole, Double-throw


Why Make a Soft Switch?

The term soft switch is used as a general term for switches made of soft and flexible conductive materials. The variety of soft conductive materials today is vast. You can find (and make!) conductive thread, fabric, yarn, velcro and raw fiber. These can be used like their non-conductive counterparts. They can be sewn, woven, knitted, felted and crocheted to create switches and circuits.

Building wearable electronics offers an opportunity to design unique switches. This is due to the introduction of these unique materials and their abilities. In this class, we focus on using conductive thread and fabric.

A switch also doesn't have to be wearable. There are many instances where a switch that is made of conductive fabric is better than a hardware switch. Conductive fabric is low profile, soft and can be cut into any shape, it can even stretch!

You've already learned that in it's most common form, a switch is made of two metal contacts that connect and disconnect. If you walk down the notions aisle of a fabric store, you will find lots of items that fit that description, such as zippers, magnetic clasps, and snaps. These all have the potential to become a switch. Think about how a pushbutton, toggle and rotary switch work, they all change states through physical means such as pushing and twisting. Designing with found notions from your fabric store, as well as fabric and thread, can lead to new interactions that engage switches. For example - unzipping a bag, putting your arm around someone, lifting up a hood or the touching of two fingers. The possibilities truly seem endless.


Designing Your Soft Switch

When designing a soft switch, there are four main parts to think about. I have defined them below. I will also be using these terms frequently throughout the class. All of the terms, except for spacer, can also be used when talking about hardware switches.

Parts of a soft switch:

Contacts
There needs to be a set of contacts that open and close in a switch. Your switch will be using conductive fabric for these.

Leads
Just like the two leads of an LED, the switch needs a lead on each contact to make it easy to connect to without interfering with the rest of the switch.

Casing
This is the outside package of the switch. The casing can be any shape and size. The material used will depend on how and where you are using the switch.

Spacer
A spacer is only needed when making a soft momentary switch. This is the layer that goes in between the two contacts when they are stacked on one another. The spacer can be made of a netting material or a thicker material, like a piece of felt with holes cut from it. The holes in the felt (or netting) allow the contacts to touch each other when pressed, closing the switch.

Now that you know what goes into a switch, let's make one!


Observe an Action

Wearable projects often map the closing of a switch to an action made by body movements or gestures.

Before you design for an action, first you need to observe it. Observing tells you where to put the switch in order for it to work and where other components should be. The final project for this class uses the action of a high-five to close a switch. Slap some skin with your friends and observe where the two hands meet most often. When giving and getting high-fives you will notice that sometimes the hands meet high, some meet low and some don't make contact at all.

The general idea is to predict how to get the result you want from the action by observing it. For this project, you want to design a switch that will close when you give a high-five, capturing and recording the action. So, the way to think about it is if you put the switch in the spot you observe gets hit the most, the probability the switch closing will go up.


Draw Switch Shape

I observed that all the high-fives I doled out made contact with the ball of my hand.

If you want to put the switch somewhere else, that's ok. Follow the steps below to create a pattern for your switch. Trace your hand and mark where you want the switch to live.


Draw a contact shape with rounded edges within the tracing. Draw in two leads. Put them in a place where they will not touch each other, a good place is on opposite sides of the switch.


Cut Contacts

Cut the contact with leads out from the tracing.

The iron-on conductive fabric you will use has one conductive side. This means that the pattern needs to be mirrored so the conductive sides of the switch touch each other. Grab a second piece of paper and use the pattern to trace the contact with the left lead. Then flip the pattern over and trace the contact with right lead.

Cut the two contacts out of conductive fabric face up.


Make Casing

The casing is made up of a bottom and top piece of felt. The switch needs to be secured to your hand. This is accomplished by putting it on a strap. The bottom casing is a long strap, the top is shorter and only needs to be large enough to cover the contacts. Use the soft measuring tape to measure the circumference of your hand where the switch will be located.

My circumference is 7.75 inches + 1" to create an overlap = 8.75" total.
The width should be no less than 1.25" which is wide enough for the switch plus some room for sewing.

Use the measurements taken from your hand to trace a rectangle onto a piece of felt. The rectangle may not be made up of straight lines. The ball of my hand curves at the top. I transferred that curve to the top of my strap by using my hand tracing.

Cut generously if unsure since you can always cut away later what you do not need.


Cut the top casing, using the strap as the pattern to get the right shape and width.


The conductive fabric you are using has a plastic coating on one side of it. When you apply heat to the metal side with the plastic side touching a piece of fabric the plastic melts. It's very simple and great to use for wearable electronics. Put your iron on the medium - high setting, this is usually the Wool setting. Place each contact on their respective pieces of felt plastic side down and use the iron to apply heat on top.


Make Spacer

The last thing to make is the spacer. Use the top casing as the pattern for the spacer layer, making it the same shape and size. Place the spacer on top of the bottom casing.


Mark and cut out one or multiple openings.


Put the top casing on, creating a sandwich and completing the switch design.


Connect to the Leads of the Switch

Take two alligator leads and clip them to each lead of the switch. Trim down the felt around the lead if the alligator clip is not making good contact. To get the alligator teeth around the lead on the bottom contact you may need to cut a little slit in the felt right next to the end of the lead.


The Basting Stitch

The switch is now ready to be sewn closed! We will be using the basting stitch. This is a stitch made for temporarily tacking fabric in place. It's very useful for prototyping since it's quick and is easily taken out. It's the same as a running stitch, except it has longer stitches.

Thread a needle with 18" of regular thread and knot the end. Baste all 3 layers of the switch together while still leaving room for the alligator leads to clip to the leads.

Knot once using the method learned in the Sew a Circuit lesson.


Test Switch

Connect the switch to the multimeter using alligator leads and pin the strap around your hand. Set the multimeter to the continuity setting. Find a friend, give them a high-five and listen for a beep. If the high-five is too quick and the switch only connects when more pressure and time is applied to the switch, make the opening(s) in the spacer larger.


Testing with the multimeter is the best way to fine tune a switch's sensitivity before finalizing the design. For example, I first had three small openings along the length of my switch, fearing that a larger one may be triggered too easily. After testing it with the multimeter, I realized that contact could not be made easily between the three smaller openings. I cut the basting stitch and pulled open the switch sandwich.

Based on the learned information, I ended up cutting a larger opening. I then sewed it back up with a basting stitch, tested it again and it worked great!

For now put this switch aside, you have one more to make!


Snap Switch

While you are warmed up, you are going to create a second switch. This one will come in handy during a later lesson. Grab the set of snaps, felt, conductive fabric and thread, this one is quick! Use the pattern you downloaded earlier in the lesson or draw it right on the material using the fabric marker.

Cut out two rounded rectangles from the iron-on conductive fabric. The size of the rounded rectangles should include the size of a snap (contact) and room to clip and sew to (lead). Cut out the same size and shape of the contacts from some felt.

Iron down the fabric with the iron on a medium-high setting. Thread a needle with 12" of conductive thread. Sew through all the holes of the snap using the skills learned in the Sew a Circuit lesson. Knot and cut to finish. Instead of just covering the knot, use the Aleene's glue to cover all the thread. It's a small amount to cover so you may as well. This way it's insulated and you don't have to worry about later.

The switch closes when snapped together and is open with disconnected! The snap can act as a connector and as an electrical snap all in one. Go ahead and test it with the multimeter to hear that satisfying beep.

As a Ground Breakout for the LilyPad USB

This may not make sense to you since we have not covered the LilyPad USB microcontroller yet. I would still like to mention it here for reference that one side of this switch will be snapped onto to LilyPad USB ground later on when you make the microcontroller removable. This will make clipping multiple things to the ground pin very easy!

Great job! Post pictures below of your completed high-five and snap switches!


Test Your Knowledge

{
    "id": "quiz-1",
    "question": "What is a momentary switch?",
    "answers": [
        {
            "title": "A switch that can stay in one state until acted upon",
            "correct": false
        },
        {
            "title": "A switch that is in one state when pressed and in another state when released",
            "correct": true
        }
    ],
    "correctNotice": "That's correct",
    "incorrectNotice": "That's incorrect"
}
{
    "id": "quiz-2",
    "question": "What does it mean is a switch is single pole, double throw?",
    "answers": [
        {
            "title": "It is two switches that work as one",
            "correct": false
        },
        {
            "title": "it has one input connected to two outputs",
            "correct": true
        }
    ],
    "correctNotice": "That's correct",
    "incorrectNotice": "That's incorrect"
}
{
    "id": "quiz-3",
    "question": "Wearable electronics offer opportunities to design unique switches because...",
    "answers": [
        {
            "title": "My mom tells me I am really creative.",
            "correct": true
        },
        {
            "title": "Soft conductive materials have unique properties that are still being explored.",
            "correct": true
        },
{
            "title": "Wire and conductive fabric work well together.",
            "correct": false
        }
    ],
    "correctNotice": "That's correct",
    "incorrectNotice": "That's incorrect"
}

High-five! You completed two soft switches! Share your switches and any observations you made below.

CLASS PROJECT

Share a photo of your finished project with the class!

Nice work! You've completed the class project