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Understanding and Building Electronic Sewable Circuits

Now that we have looked at the history, current work, and ethics of making and testing wearables, it’s time to jump into the electricity basics. Understanding and making electronic circuits is important for your wearable journey. We will work through the principles of electricity. Recognizing the principles will help you to follow along with the activities in this book, and it will also help you to plan and make your own wearables.

In this chapter, you will learn the first steps of understanding electricity and then using switches in a circuit. Once the basics have been covered, you will build electronic circuits with Light Emitting Diodes (LEDs). This foundation will set you up with the nuts and bolts of your new skills so that you can apply them to a sewable circuit. Also, we will learn how to use a multimeter and why this is an important tool when working with electricity.

By the end of this chapter, we will get hands-on with some practical examples. To put it all into practice, you will use conductive materials and conductive thread, alongside other materials. You will make working circuits in fabrics. Learning through doing will become the foundation for your continued journey.

In this chapter, we’re going to cover the following main topics:

• Understanding electricity
• Using a multimeter
• Electronic circuits
• Soft circuits
• Switches and buttons

Technical requirements

This chapter will have a practical element where you can try building the circuits that are in the book. The best way to learn is by doing. These are the recommended items for the circuits. Note that for easier sourcing, all of these items can be purchased in a single kit, including the technology and fabrics, with additional items for future chapters (not including the multimeter) from https://www.tinkertailor.tech/product-page/busy-new-bee:

• Various LEDs, a 5 mm through-hole, and sewable LEDs.
• 220 Ohm (also noted as Ω) /330 Ohm resistors.
• A 3V battery (CR2032), which is also called a coin cell.
• Crocodile clips; 5 or 10 is a good number.
• A breadboard; you can use half sizes or full sizes.
• Hookup wire:

This is measured in gauges, for instance, around 22AWG solid core will make prototyping easier for these circuits; 1 meter will be enough. When using a hookup wire for a breadboard, a single-core wire maintains its shape well and is easy to push through the breadboard holes. For wearables, we often use stranded wire, which is a lot more flexible because it is made up of several “strands” of wire. This can be more difficult to push into a breadboard. Usually, you will need to hold the strands together and twist them to form a more solid end.

• The Adafruit Beginner LED Sewing Kit (ID:1285) can be found at https://www.adafruit.com/product/1285#tutorialsstarter. It contains the following items:
  • 2-ply conductive thread
  • 2 x sewable battery holder for CR2032
  • LEDs
  • 5 mm sewable metal snaps
  • Sewing needles
• Material/fabric: You can upcycle clothes or use soft acrylic felt. Alternatively, denim is a good first choice. We are looking for a fabric with some bend but that is thick enough to be held into place easily to sew.
• Conductive fabric: This could be a silver-, steel-, or copper-based fabric, along with various conductive items (optional).
• Multimeter.

If you are new to sewing, you might find a threader more useful. This makes threading our needles a lot easier to do. When using conductive fabrics, this is especially true as the thread can be more difficult to thread. Now that we have our items ready to use, we’ll get started with learning about the basics of working with electricity. We’re working with low voltages, so most of our components and circuit boards will only ever use 5V or 3.3V. We are learning about electricity using low voltages, don’t ever attempt to use mains electricity without the proper learning required.

Understanding electricity

Let’s start with electricity basics to begin our journey of making wearables. We will cover the following:

• What is a circuit?
• Resistance
• Voltage
• Current

The preceding list highlights three main properties that we need to understand to build our circuits: resistance, voltage, and current.

These three properties connect and have a relationship called Ohm’s Law. It’s important that we understand these properties to help us build and fix our circuits. Also, when you have finished the exercises in the book, you will have the confidence and skills to create your own projects. Let’s explore them in detail, starting with circuits.

What is a circuit?

A circuit has a start point and an endpoint with an electronic component in between. It forms a loop. This allows electricity to flow. Between the start point and the endpoint, there can be many other connections. Circuits can consist of components such as resistors, sensors, motors, and more. We will begin with a few components and work up to using a few sensors and outputs.

For electricity to flow, we must use conductors, which are items that allow the current to pass through them. Insulators will stop the flow. Common conductors include metals, water, human skin, and plants.

Common insulators, which stop the flow of electricity, are plastic, rubber, dry wood, and glass. Figure 2.1 shows a closed loop that moves the electricity from one point to another. It is a schematic diagram that is used to show the electrical representation of this circuit. It also shows a simple circuit with the current flow from positive to negative. In this diagram, you can see the power symbol on the left-hand side. Electricity will flow out the top, on the + positive side, and follow through the resistor. Then, it will flow through the LED, which will light up, and then the complete circuit returns to the power symbol, on the ground side, -:

Figure 2.1 – Schematic of an LED circuit (left-hand side) and the LED circuit (right-hand side)

In the Using a multimeter section, we will take a closer look at how we can determine whether an item is a conductor or an insulator.

Note that a schematic drawing is representative of all the components needed and how they are connected. It is not how they are physically located on a circuit. The physical circuit has a battery and an LED. A diode is a component that conducts electric current only in one direction.

What’s a Short Circuit?

A short circuit happens if you connect power and ground directly. If you complete a circuit with no components in between, a short will happen. This will burn out your power source quickly and cause damage, so be careful. Be aware of anything in your circuit becoming too hot. Turn off the power immediately.

Why is a circuit important? When we make our wearables, we use circuit boards to control the inputs/outputs:

Figure 2.2 – Printed circuit boards (PCBs)

A circuit connects the boards to our components by turning them on or sending and receiving data. If we connect the electronics correctly, we can control them.

Once we learn how to connect our circuits, we can program them, so this is the first step. A printed circuit board (PCB) has components connected with metal traces. See Figure 2.2, which shows some examples of PCB boards. As an insulator, it does not conduct electricity.

The conductive material between components carries the electricity in a loop to make the circuit. This will be the same as when we use wires to complete our circuit. The PCB is part of the development process journey. When making a wearable project, we often go from prototyping on a breadboard, to creating a soft circuit, then make it more durable by bringing it to a perfboard or protoboard for soldering (perforated or prototype), and lastly, to PCB.

Open circuit

If you don’t connect all the parts, this can result in an open circuit. If your wires are not connected, then the circuit just won’t work.

If your circuit isn’t working, it is a good idea to check that all your connections are connected where they should be. Sometimes, a wire has come loose or become broken, and this will be the reason why it isn’t working. Sometimes, components flicker when they shouldn’t, so if you see a flicker, look through your wires in case you have an open circuit. In Figure 2.3, we can see the vibration motor has a ground wire that has come off. That’s why it isn’t working:

Figure 2.3 – An open circuit

Checking through your connections can easily and quickly fix an obvious error. It’s always worth looking over your circuits if things aren’t behaving as they should.

Circuits Not Working?

An open circuit can happen in our sewable circuits. Threads can easily break or rub against other conductors or insulators, altering our intentions for the circuit. So, always check your threads.

Let’s take a closer look at the three terms you will come across for your circuits: resistance, voltage, and current.

Resistance – Ω

Resistance restricts the electrical flow or charge in the circuit. This is measured in Ohms, Ω, and the symbol is R. Resistance is very important for our circuits. If there is too much resistance, the components won’t work because not enough electricity is getting to them, for example, an LED won’t light up. However, if we have little or no resistance, then the component will burn out. If that happens, you won’t be able to use it again.

We can see this visually when using different resistors. Using different values for resistors will alter the brightness of the LED – less resistance will allow more power and the light will be brighter. A resistor can be used in either direction.

Voltage – V

Voltage is the potential flow, measured in a unit called a Volt. The symbol is V. The source of electricity has two sides: positive and negative. Voltage flows from the start of the circuit or the highest electrical potential, positive +, which is power, to the endpoint, ground -. Common ground is known as zero Volts, with no electrical potential. The voltage is the difference in electricity between any two points on the circuit. In our wearable circuits, we will have a positive voltage of 5V or 3.3V and a negative voltage of 0V. It is very important to always check the component you are using and what its maximum voltage is.

Many of the components we use need 3.3V, so they will need to be connected to a similar power source. We will cover this in greater detail later.

Current – I

Current is the amount of electrical flow in our circuit. As described in Ohm’s law, current has the symbol of I. This is the rate at which the charge is flowing. It is measured in Ampere, or amp for short. The unit symbol is A. For our circuits, you might also see it as milliamps (mA). You will also see milliamp Hours (mAh), which is a measure of the current delivery capacity of a battery.

Remember! Red = Power and Black = Ground

For positive (power) connections, I use the convention of red wires. I use black for negative (ground). Many people follow this same convention. It makes it easier to find errors in our circuit, as we can quickly identify where our power and ground are coming from.

Now we can put the formula together using resistance, voltage, and current using Ohm’s law to calculate values.

Ohm’s law

Ohm’s law tells us that voltage (V) is equal to current (I) times resistance (R):

V = I x R

The equation can be rearranged to work out what the values are for your circuit. So, we can use I = V / R or R = V / I. We can use Ohm’s law to calculate the resistance of the circuit. For example, if you want to know the right voltage for powering an LED, we can use V=IR.

Activity 2.1 – creating a simple circuit

The simplest circuit we can create is an LED with a battery. Figure 2.4 shows the schematic for a simple circuit. A power source and an LED form a complete circuit. Because the battery is only 3V, we don’t need to use a resistor. If we do use a resistor, we can light the LED for longer. All we need to do is hold a coin cell battery between the legs of the LED (Figure 2.4). Because we are hitting the highest threshold of voltage an LED can take without burning out, we are limiting the lifespan of the LED. Think of it as burning the LED at full power. To extend its life, we use resistors to drop the voltage so that the LED will light and burn for longer. You could add a second or third LED to lower the brightness too.

Figure 2.4 – The schematic for the simple circuit (left-hand side) and an LED circuit (right-hand side)

This is also a quick way to check the polarity of your battery. Usually, I keep a coin cell with or near my LEDs as it’s such a handy way to check. This is because you need to hold the positive leg (the longer leg) of your LED to the positive side of your battery. The negative leg (the shorter leg) of your LED needs to be touching the negative side of your battery:

Figure 2.5 – LED polarity

Quick Tip

A tip for figuring out LED polarity is that the long leg is the positive leg. If you’ve cut the LED legs and you aren’t sure, look at the small rim of the LED: it has one flat side. This flat side is the negative leg. Also, you can hold the LED up to a light and look inside it. There are two pieces of metal. The smaller one connects to the positive leg.

Generally, in a single circuit, we can light an LED with a 3V battery:

Table 2.1 – How long the LED will be lit for

We’ve had a look through the information to understand electricity, and we are gaining an understanding of resistance, voltage, and current. To see what’s happening beneath the surface and learn more about current and electricity, let’s look at how to use a multimeter.

This is an essential tool for creating wearables. Using a multimeter is important because we can fix broken circuits, work out resistance, and check what materials are conductive.

Using a multimeter

We can use a multimeter to measure resistance, voltage, and current. It’s a great way to see what’s going on in our circuit. Using a multimeter, we can check our connections and find breaks in the circuit; it tells us when something is broken. Multimeters, as shown in Figure 2.6, come in different sizes and prices. Starting with a low-cost one will be suitable for our circuits. I have a small portable one. They have a dial so that you can select the function you need. A multimeter will have probes that we’ll use to connect to the circuit to take measurements. You’ll notice these are also black and red, following the same convention we’ve been using for our circuits, too. If your probes are removable, make sure the black probe is in the COM port and that the red probe is in the mAVΩ port. Additionally, note that the multimeter uses the convention of red wire for positive/power and black for negative/ground. You should read the instructions that come with the multimeter you buy, as they might have slightly different dials:

Figure 2.6 – Multimeters

In this section, we will be learning about the important ways multimeters can help in our circuits, covering the main ways you’ll be using the multimeter. For additional learning, there are tutorials and videos online if you’d like to take it further.

Resistance

Let’s measure a resistor. Resistors are often out of their packages or mixed up in their packaging, and this is a quick and easy way to find out whether we have the right one:

1. Turn the dial on your multimeter to the Ohm symbol, Ω, and place the probes on either side of the resistor that you want to measure.
2. Figure 2.7 shows the probes on each side of the resistor, and the reading on the multimeter is 217 Ohms.

When you buy it, it’s marked as a 220 Ohm resistor. Be aware that there is usually a difference in the readings. There is a tolerance value to resistors.

The common resistors we are using are usually plus or minus 10 percent, which won’t make much difference to our circuits:

Figure 2.7 – Measuring resistance

If you can’t hold the probes steady, you can make this easier by using use crocodile clips, attached to the probes and the component or part. You can check the resistance of the conductive thread or materials in your circuit. This is especially important if the thread has some distance to travel between components, which adds resistance (that is, less electricity) to the connection. An auto-ranging multimeter will find the correct range of your resistor. If your multimeter doesn’t do this, you’ll need to move your dial to the correct range:

Figure 2.8 – A close-up of a multimeter dial

Typically, when measuring a resistor value, you turn the dial to Ω, and then turn the dial to 2000. This will measure values under 2000; for example, LEDs will use 330 Ohms or 220 Ohms. If we are using a higher value, such as a 10K resistor, you would turn the dial higher, to the 20K setting.

You can also use a guide to calculate the resistance value yourself. One helpful resource can be found at https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-resistor-color-code.

Voltage

It’s useful to be able to check the voltage of your battery, as this can often be why your circuit isn’t working. You can check whether your components are receiving the amount of voltage they need. Figure 2.9 shows a battery being measured at 3.8V:

Figure 2.9 – Measuring voltage

Turn the dial on your multimeter to the V with a straight line. Place the probes on correctly according to polarity: ground to the black probe and power to the red probe.

If your multimeter has multiple settings on the dial for voltage, then turn the dial to the DC Voltage portion of the dial and choose a voltage higher than what you are expecting. Arduino circuits use 5 volts, so your dial should be set to 20V, not 2V. You’ll know whether this is incorrect, as it will display the voltage incorrectly. If it’s wrong, then move it to a higher voltage.

Current – continuity/conductivity tests

This is a quick and easy way to check whether your circuit is complete or whether the material you want to use is conductive. I have a portable multimeter that I can carry with me and use in shops if I’m curious about a piece of fabric, thread, or other material.

If you are unsure whether your wiring and connections form a closed circuit, perform the following steps:

1. Turn your multimeter dial to the speaker/audio icon. It’s a little speaker because this test will make a sound. There will be a tone when there is a closed circuit.
2. Place the probes across the place you want to test. This could be across a wire you’ve soldered for example. It might be to see if a fabric is conductive. If you hear the tone, then it is a complete circuit.
3. If you want to check a broken circuit connection, place the probes onto the wires, pins, or part of your circuit are not supposed to be connected. If you hear a tone, that tells you it is connected, there is flow of electricity, when there shouldn’t be. Note this is purely the physical circuitry, and it can’t tell you whether your circuit will work according to your programming.

Figure 2.10 – Measuring no conductivity, shown with OL (left-hand side) and conductivity registering a value (right-hand side)

Do you want to know whether it is a conductor or an insulator material? We can check conductivity. Again, turn the dial to the speaker symbol and place the probes in two separate places on the item you want to test. In Figure 2.10, you can see the reading is OL, which stands for Open Loop, so there is no conductivity between the two probes. This is a measurement of felt fabric. Often, I use felt to put my components on and map them out. However, in Figure 2.10, we can see that conductive fabric is being measured. Again, look at the reading; this material is conductive and shows a positive value reading. You will hear a tone, so we know we can use this conductive material because it will carry the current.

Some fabrics will have some conductivity in a different direction from what you are testing. Try testing the fabric in a few different directions according to the way it is woven because it might have conductivity. Then, you can use the fabric in that direction and sew on top of it.

Important to Remember

The probes must not touch each other when doing the reading. You’ll notice that when the probes touch each other, you will hear a tone. That’s because you are forming a closed circuit. So, if the probes touch, you are measuring your multimeter circuit and not the material.

The multimeter is a valuable tool to check our circuits, the flow of electricity, our battery charge, and whether a material is a conductor or an insulator. Now that we understand the basics of our multimeter, we will continue our journey into electronic circuits. We’ll be using the multimeter again to help us work out the resistance when we have more than one resistor in the circuit.

Electronic circuits

Let’s create some circuits. First, we will use crocodile clips, a battery holder, a battery, and LEDs to complete two circuits. We will look at circuit design with the following:

• Electricity in series
• Electricity in parallel

As we learned previously, as electricity travels through a circuit and its components, from a point of higher voltage to lower voltage, the electric potential is used up by the components it flows through until there is no more potential energy. So, how we arrange our components will influence how the electricity is consumed. Let’s look at series and parallel circuits, using an LED to demonstrate.

Series

For components to be in a series, they are connected one after another. Electricity will pass through the first component, then through the next, and so on:

Figure 2.11 – A schematic LED in a series

The schematic shown in Figure 2.11 shows three LEDs in a series. We can also see how this might look in a circuit using two LEDs. A quick way to see whether it is in series is to follow the current flow: start from the positive side of the power source and follow through to ground. The electricity gets used as it passes through each component before going to the next. If we don’t have enough voltage, then only the first or second LED in a series will be lit. This is called a voltage drop. As electricity passes, it drops that voltage.

Typically, the LEDs we use have a forward voltage drop of 1.8V–2.2V. If we used a 3V power source, then the first LED would work and the second would get less voltage and work with less brightness. There wouldn’t be enough voltage left to power any more LEDs on. You need to choose a battery with enough voltage – or you can wire up your components in parallel.

Parallel

Each component will receive the same amount of voltage, but the current is divided between them. If we wire our components side by side, they are in a parallel circuit. Electricity will pass through them all at the same time.

They are each connected to ground and power. This is shown in Figure 2.12 where each component has a circuit that functions independently:

Figure 2.12 – A circuit in parallel

Figure 2.12 shows one LED is lit while the others are not. With a parallel circuit, we can see that there are distinct paths the current can take.

What else can be in series or parallel?

Using a resistor in series – where the electricity can only follow one path – means that if we add resistors, we add their values together. If we used three 10K resistors, the total resistance would be 30K. In a series circuit, the current is restricted to the same path, making it harder to flow. Using a multimeter, we can easily see the resistance when we add our resistors. Take a look at Figure 2.13, showing over 29K Ohms:

Figure 2.13 – A series circuit with almost 30K resistance (left-hand side) and a parallel circuit with just over 3.3K resistance (right-hand side)

Resistors in parallel circuits work differently. There is more than one path for the circuit to take when we are parallel. Our supply voltage is the same, but there are more paths. If we have one 10K resistor, then it will have 10K resistance. However, if we have two 10K resistors, then each takes the electricity flow through it at once, making it half, resulting in 5K resistance. If we are using three 10K resistors, that results in 3.3K resistance.

Now that we understand the types of circuits we can make, let’s put it all into practice! We’ll use crocodile clips to test a circuit.

Activity 2.2 – using crocodile clips to create a circuit

Crocodile clips, also called alligator clips, are great for creating a temporary circuit. This is useful when we are connecting to fabrics or other soft components that won’t easily fit into a breadboard. There are many different types. Figure 2.14 shows the variety – some are very short and others a lot longer. My desk easily gets cluttered with these, so I like to use the shorter ones. Some also have what are called DuPont cable ends. This is a plastic connector on the wire ends, that have a plug (a metal pin) or socket version (a corresponding connector with metal inside to accept the metal pin):

Figure 2.14 – Crocodile clips and DuPont ends

You’ll find having a range of these clips is very handy for connecting components quickly and easily.

Our parts and the final circuit, as shown in Figure 2.15, include a battery holder, a battery, crocodile clips, and an LED:

Figure 2.15 – Parts for the circuit (left-hand side) and the complete circuit (right-hand side)

Now that we have our parts and can see the finished circuit, let’s put it together.

To connect the LED circuit, perform the following steps:

1. Connect the black crocodile clip to the - ground side of the battery holder.
2. Connect the red crocodile clip to the + power side of the battery holder.
3. Connect the short leg (ground) of your LED to the other end of the black crocodile clip.
4. Connect the longer leg of your LED (positive) to the other end of the red crocodile clip.
5. Put in your battery.

We have light! We don’t have a switch yet though, so it stays on when the battery is in. We will improve this circuit later.

Now that we’ve created this circuit, let’s use a breadboard to move our circuits once again. You will likely use a breadboard for most of your early prototyping because it’s a quick way to check whether things are working as intended.

Activity 2.3 – creating a circuit using a breadboard

Using a breadboard is a great way to start prototyping your circuit. It can be more reliable and easier to move when you’ve used wires in a breadboard. If your circuit works and you have finished, we can solder or sew the components to create a permanent project.

A breadboard is a piece of plastic (Figure 2.16) with metal strips inside. These connect all the small holes on the top. The horizontal edges of the breadboard run horizontally. The smaller vertical strips run vertically. This means everything in that row will be connected:

Figure 2.16 – A breadboard

If your breadboard has a red/black or red/blue strip on it, the long red horizontal strip is used as a power rail. Once you put power into it, it will power any components that are also connected to that rail. A breadboard is a much quicker way to prototype than having to sew all your circuits the first time. It can help solve a lot of errors:

Figure 2.17 – Various breadboards

To make our circuit on a breadboard, we need (as shown in Figure 2.18) a breadboard, a battery holder, a battery, an LED, and jumper wires:

Figure 2.18 – Parts for the circuit (left-hand side) along with the completed circuit (right-hand side)

To understand how to connect (the completed circuit is shown in Figure 2.18, on the right-hand side), perform the following steps:

1. Using a red wire for power, connect the red wire to the + power side of the battery holder.
2. Plug the other end of the wire into the red power rail of the breadboard along the horizontal bottom (as shown in Figure 2.18 of the completed circuit).
3. Using the black jumper wire, plug it into the - ground side of the battery holder.
4. Push the other end of the black wire into the horizontal ground rail on the breadboard. You now have power and ground in the breadboard for your circuit.
5. Push the LED legs into the breadboard. Make sure the legs are in two different vertical rails. For example, the ground leg is in row 20 and the power is in row 22. Use any rows:

Figure 2.19 – A battery holder and an LED in a breadboard

6. Use a red jumper wire to power the LED. Push one end into the same row as the positive side of your LED (the longer leg); I’ve used row 22. Push the other end of the red wire into the horizontal power rail.
7. Plug the black jumper wire into the same row as the short leg of your LED (ground); I’ve used row 20. Finish the circuit by plugging the other side of the black wire into the horizontal ground rail of the breadboard.
8. Finally, put your battery into the battery holder.

You should now have an LED that is on and giving light. After completing this activity, you understand how a breadboard works and how to use it. Also, connecting ground and power in a circuit will be easier to figure out now that you’ve done it! If your LED isn’t lighting up, check the legs are the correct way around. Maybe you have connected the ground side to the power side by mistake. Now, take some time to try different designs on the breadboard to better understand the layout of the breadboard and the circuit.

Now that we have created a circuit with crocodile clips, and one on the breadboard, it’s time to get conductive! Let’s work through a circuit using conductive thread to solidify our learning and continue our journey into wearables.

Soft circuits

We’ve been learning about the importance of testing our circuit on a breadboard and what happens when connecting components in series and parallel circuits. Now, let’s look at LEDs, conductive threads, and conductive fabrics. Once we understand their foundations, we can create a soft circuit.

LEDs

LEDs come in many sizes and types (Figure 2.20). They can suit a huge range of purposes. It is a good idea to have a look online at some of the LEDs you can get so that you don’t limit yourself to just using the most common ones. In this chapter, the LEDs are 5 mm, but they can be as small as less than a millimeter. They are low power, have a long lifetime, and are robust.

Some common places where you’ll see LEDs are control panels, computers, traffic lights, car lights, electric toothbrushes, and streetlights. LEDs have a range of colors, opacities, and light intensities. The higher the voltage the higher the lumen, and the greater the intensity. Often, I see ultra-bright LEDs and some that are directional. Additionally, the light is very bright straight on, but not very visible sideways:

Figure 2.20 – LEDs

You can also buy flashing, bi/tri-color, and rectangular LEDs. For our projects, we will be using 3V LEDs – that’s the one parameter you’ll need to be careful to choose. This is because they can easily be controlled by input/output (I/O) pins. Later, we’ll be using I/O pins with microcontroller boards.

Conductive threads

Conductive thread is great for circuits. It carries the current in the same way that wires do. This allows us to create flexible, soft circuits, without soldering. There are silver and steel-based threads, but there are also a lot of conductive materials that can be used (Figure 2.21). If you test the material with your multimeter, you’ll know whether you can use it to carry electricity.

Because of the differences in the threads, it’s best to try a few and decide which is best for your wearable project. Silver threads are often nylon-based, so they can’t be soldered either. Lastly, silver thread can tarnish over time due to their silver content.

Steel-based ones are a little more rigid and can be soldered – with some practice. Also, if your components are very far away from each other, for reliability and longevity, you will want to eventually swap the sewing out with soldered soft (silicone) wires:

Figure 2.21 – Conductive threads for circuits

Because conductive thread conducts electricity, if your threads touch each other, it will create a short. Remember, a short will stop your circuit from working. The battery releases energy very quickly when there is a short, and that can cause heat, smoke, sparks, and more. When you plan out your project, make sure that you plan a circuit that won’t have overlapping threads or that you know where to cover your thread to insulate it. You can insulate with thick fabrics, electrical tape, fabric paints, certain glues, a hot glue gun, 3D printing pens and plastics, and more.

Conductive fabrics

How do you know if a piece of fabric is conductive? We’ve seen how to use our multimeter to test the conductivity. This will help us decide what materials to use.

Try using the resistance measurement on your multimeter to see whether it registers there. A material is conductive if it can carry an electrical current.

The fabrics available can vary greatly. Figure 2.22 shows a small section of what is available. These materials come in knits, jersey styles, rip-stop, and more. Some have a back sheet on them that allow them to iron onto another fabric easily. The conductive iron-on fabric can make it simpler to test out your design, as you only need to cut out the shape in the fabric and then iron it into place. If your fabric has folds in it, it’s best (as it is with all fabrics you use) to iron it first to remove any folds or creases. Bear in mind that electronic fabrics will heat up. Iron carefully and only a small corner first to test your temperature. Some materials can scorch easily.

Here is a list of considerations to understand the type of fabric you can use:

• Will it fray?
• Will it wrinkle easily?
• Will it be too stretchy or not stretchy enough?
• Will it be too heavy?

Remember that conductivity varies greatly between the different fabrics, so always test that it will work well in your circuit before buying huge amounts:

Figure 2.22 – Various conductive fabrics

You can find a variety of conductive materials from the Adafruit website, which has great supporting documentation: https://www.adafruit.com/category/845. For UK-based readers, I’ve found silver, copper, nickel, and tin materials at https://www.hitek-ltd.co.uk/technical-textiles and a large supply of conductive textiles and materials at https://www.tinkertailor.tech/conductive. Note that nickel is used in most components, so be careful if you have a nickel allergy. Also, try not to have wearables with bare components that constantly touch the skin if not part of the interaction.

The Shieldex product range is one of the main supplier; you can view it at https://www.shieldex.de/en/applications/. As shown in Figure 2.22, information about the materials is helpful for gaining an understanding of their unique properties. You might have a local supplier that you can find and ask to purchase a sample pack. This is a great way to try small patches of fabrics before you buy larger quantities.

Many of these fabrics and materials are made for medical purposes. You’ll notice there are materials with antiviral and antibacterial properties, and I’ve seen some that are sold, such as copper, to put on door handles to make viruses harmless in a short space of time. Additionally, you might have noticed that the tips in many gloves have a small pad of conductive material to allow touch screens to work.

After our look at LEDs, conductive threads, and fabrics, it’s time to get sewing. Let’s make a sewable circuit!

Activity 2.4 – sewing with conductive thread and LEDs

Now that we’ve learned about LEDs and conductive thread, we can make our soft circuit. For this example, we will be using the starter kit from Adafruit (or its equivalent components), which is available online at https://www.adafruit.com/product/1285#tutorialsstarter.

By the end of this activity, you will have sewn a circuit that is the same as the one we mapped out on the breadboard earlier. It’s important to be able to take our circuits from a breadboard to fabric, and Chapter 8, Learning How to Prototype and Make Electronics Wearable, will cover this in more detail later. For now, let’s get making!

Important Note

Always disconnect your power source before sewing the components or connecting them with wires!

The components needed to create this circuit are conductive thread, an LED, a battery holder, and a coin cell battery (Figure 2.23). You’ll also need a sewing needle:

Figure 2.23 – The items needed for the circuit

Now we can prepare our components for a soft circuit. You’ll need to get an LED, which we will shape so that we can sew it onto the circuit!

Through-Hole and Surface Mount

Through-hole, or thru-hole, mounting refers to the mounting technique of a component. If it is a component with legs, typically, these legs go through the holes drilled into a PCB. We call it a surface mount (SMT) component if the component stays on top of the PCB – no legs! Usually, they are very small and held by solder paste onto a board.

Let’s use a through-hole LED as part of our circuit. We can shape it so that it will fit into a wearable design.

Preparing an LED

To sew a through-hole LED, it helps if we can use some pliers to bend the legs so that they are much easier to sew. Figure 2.24 shows a quick way to alter your components. First, straighten out your LED legs so that they lay flat. Then, take one leg and hold it with the tips of the pliers.

Keep holding the leg and begin to turn the pliers to create a loop. Take a look at Figure 2.25, which shows that process. Do this on both LED legs and then flatten it so that you can sew through the holes. You can do this with resistors and other components that have legs:

Figure 2.24 – Steps for the LED legs

I have a pair of small bull-nose pliers (with a square-shaped end), and that creates a square shape, not round. So, play around with what you want from your circuits and how you’d like them to look. You might want to bend them into different shapes to easily distinguish between + and -:

Figure 2.25 – Preparing an LED

Also, you might want to choose a needle with a slightly larger eye. The conductive thread can be thicker and fray more than a typical sewing thread. You might want to use a threader to make it easier and quicker to thread the needle:

Figure 2.26 – Mapping out your circuit

First, I mark out my circuit on felt or fabric with a pen or piece of chalk. This is to ensure that there will be no shorts or overlapping wires. If some do overlap, I can plan to insulate them. Figure 2.26 shows the mapped-out circuit. I’ve used red to indicate power and to remind me which way the LED should be.

Steps to create a soft circuit

This is optional: at the start, glue your components to the fabric you are using. This helps to hold your components in place as you sew. Sometimes, things move when we sew and can become unaligned. It can make a tidier circuit.

Step 1 – the ground side

Perform the following steps:

1. Measure out a quantity of thread. Cut your thread with very sharp scissors to make it easier to thread. Thread the needle. I fold the thread in half once it’s threaded, so it’s double thickness. Tie a knot at the end.
2. Begin your stitching. Push the needle through the ground side, -, sew tabs of your battery holder.

Figure 2.27 shows the needle coming through the back side of the fabric through the battery holder. Be careful not to pull the thread all the way through to the other side:

Figure 2.27 – Starting your sewing

Stitch back down alongside the sew tab to go back through the fabric (Figure 2.28):

Figure 2.28 – Sewing the battery holder tab

3. Make sure that you put a knot in the end, so your stitching stays in place (Figure 2.29):

Figure 2.29 – Tying a knot on the underside

4. Sew a loop or two through the battery holder sew tabs to make sure they are secure.
5. Stitch all the way up the length of the ground side. We are using a straight or running stitch (Figure 2.30). This is a stitch where we pass the needle in and out of the fabric at the same distance.
6. When your stitching has reached the ground leg of the LED, sew around the bent leg loop you made earlier until it is secure (Figure 2.30):

Figure 2.30 – The running stitch and the stitches securing the LED

When the LED leg has been securely sewn with a few stitches, knot the end of your thread on the underside of the fabric, as shown in the following photograph:

Figure 2.31 – Stitches securing the LED

Ensure that you don’t have any long threads remaining, as this can cause a short in your circuit. Cut any ends short after knotting.

I put a dab of fabric glue or clear nail polish (Figure 2.32) on this knot to stop it from fraying or coming loose. Sometimes, the conductive thread can separate easily or have small fragments come off. This can cause a short, so covering it with a little nail polish will help prevent that, too:

Figure 2.32 – Securing the knot

Now that we’ve completed half the circuit, we can start to sew the positive side, where we follow the same instructions.

Step 2 – the positive side.

Perform the following steps:

1. Re-thread your needle with a new piece of conductive thread. Follow the same steps as earlier, but this time, push your needle through the back of the fabric to go up through the positive side, +, of the battery holder. Loop it to make it secure.
2. With a running stitch, sew along to the positive side toward the positive LED leg.
3. When at the LED, secure the leg with several stitches to loop it tightly.
4. When done, stitch through to the back of the fabric and tie a knot to secure it.
5. Trim the ends, and dab some glue or nail varnish onto the knot to secure it.

Notice that, on the back of your circuit, the two stitched areas are not crossing in any way. If they cross or touch, your circuit will short.

Hopefully, you can now put your battery in, and your circuit will work. See Figure 2.33 for the finished front and the finished backstitching:

Figure 2.33 – The finished circuit from the front and the back

Congratulations! You’ve sewn a soft circuit and are well on the way to more complicated wearables!

Circuit not working?

If your circuit isn’t working, you should check that your battery has full power. Swap out your battery. Also, check the polarity of your battery. The current flows in one direction, so you must have the LED legs in the correct position of your circuit. Check whether it is the following:

• Ground to ground: Is the ground (negative) sew tab from the battery holder and the ground (negative) leg on the LED connected through your sewing?
• Power to power: Is the correct side of the battery holder with the power (positive) sew tab sewn up to the power (positive) side of the LED (longer leg)?

Are there any shorts in your circuit? Does the thread touch a part of the circuit that it shouldn’t?

If your circuit is flickering, or only working sometimes, then check for loose connections. The sewing on the connections needs to be tight. If there is movement, it can sometimes flicker as the current isn’t constant. This is easily fixed: pull the thread tighter or sew on top to ensure you have a good connection.

Lastly, make sure there are no long ends of thread or any frayed thread pieces on the fabric. Any extra conductive material can create inconsistencies in your circuits, so it’s good practice to ensure everything has been trimmed away.

Challenge yourself!

Get creative with soft circuits. Figure 2.34 shows circuits created in a wearable workshop (and Ahmed Zia wearing his pocket bear design). First, he mapped it out and then used straight stitches to connect it. He covered the LEDs with felt to create the effect:

Figure 2.34 – Fun soft circuits created in a workshop

Now that you’ve learned about circuit types, how to use a breadboard, and taken a circuit from breadboard to creating its equal as a soft circuit, we can move on to sewing a creative circuit. This activity will consolidate your learning so that we can move on to more advanced topics with switches and buttons.

Activity 2.5 – sewing a creative circuit

Now that you’ve created your first soft circuit, let’s add a few more components to it. We will use a few more LEDs and some sewable snaps to create a circuit that we can turn on and off.

We will use another battery holder, a battery, snaps, conductive thread, a sewing needle, and some sewable LEDs. These are a little different from what we used earlier. See Figure 2.35, which has a board of 10 sewable LEDs. These have sewable tabs, so we don’t need to bend the LED legs:

Figure 2.35 – Materials for the circuit

The first part of your design will be to plan it out. What are you interested in making? A wrist wearable, a strap for your bag, or something else? I’m going to make the circuit on two pieces of gray felt, and then sew them to a vest I have at the waist. When I close the vest with the snaps, the LEDs will light up. Do you have something similar that you’d like to try?

Let’s sew a parallel circuit so that all the LEDs get the same power at the same time. To make this circuit, follow these steps:

1. Measure out your fabric against the item you will be sewing. I’ve got a vest handy, and I’ve measured out where I’ll be putting the circuit.
2. I measure it out and use a small cutting board to cut the felt straight and put it on top of the garment to check that it is the correct size. Figure 2.36 shows the process of cutting and placing the fabric piece that you cut earlier and place it were you will sew it, to check it is the right size:

Figure 2.36 – Cutting the fabric and checking the measurement

3. Next, it’s a good idea to lay out your circuit. Figure 2.37 illustrates what I’ve done.

I’ve folded back one end on each piece of felt. When I sew the snaps, it’s thicker to make sure the snap doesn’t pull through.

4. I put a little fabric glue under the flap, and I hold it into place while the glue dries with little sewing clamps:

Figure 2.37 – Preparing your circuit

5. Glue down your components with fabric glue so that they don’t move when you sew or use a glue gun, which is quicker. You might want to glue the battery holder to the underside so that it isn’t visible from the front of the fabric.

This is optional: I like to draw out the circuit stitches first to be sure none overlap. It’s a good habit to get into and can save you a lot of mistakes in the future as your circuits become more complex. I’ve been caught out with an overly complex circuit that had too many crossing wires that I should have thought through before I started to sew.

6. Put your snaps in place and make sure they line up.

Now that everything has all been laid out correctly, let’s start sewing with conductive thread.

Tip

Close your snaps together and put them on the fabric so that you are sure which way round they go.

To sew the first part of your circuit, perform the following steps:

1. Measure a piece of conductive thread and thread your needle. Starting at the positive end of our battery holder, sew up to the snap. Make sure that you go through the snap several times so that it becomes secure and that we have enough thread to conduct the current of electricity.
2. Secure with a knot. Dab glue or nail varnish to stop the knot from fraying. Cut the thread ends short. Figure 2.38 shows the knot and nail polish process.
3. Now, sew the other side of the battery. Start a new thread, and sew from the ground side of the battery all the way up to the other snap. Secure the snap with several loops of thread on all the snap holes:

Figure 2.38 – Dabbing the ends with nail polish to secure them

4. With both sides of the battery sewn, we can test our circuit to see whether this part has a good connection.

Use one of your LEDs and place the positive side on top of the positive side snap. Then, fold over the fabric with the negative snap to cover the negative side of your LED. Figure 2.39 shows how to do this. If it lights up, well done! Your circuit is halfway there and is already working:

Figure 2.39 – Testing our circuit

So, we’ve finished part of this circuit and tested it. Now we need to sew the other side of the circuit.

To sew the other side of the circuit, the LEDs, and the back of the snaps, follow these steps:

1. Let’s sew the other half of our circuit. The LEDs need power and ground to light up. Starting at the positive side of your LEDs, sew the bottom LED positive sew tab several times to secure it (Figure 2.40).
2. Continue to sew all the way up to the next LED positive sew tab and, again, secure it with several stitches. Sew up to your third LED, and sew that one in place, too:

Figure 2.40 – Starting to stitch

3. Once all three LEDs have been sewn, continue to sew stitches up to the snap (Figure 2.41). Sew the snap securely to ensure it won’t break. Then, sew back one stitch to tie a knot:

Figure 2.41 – Sewing up to the snap

To keep our stitches hidden, we can do a different stitch. If you sew the longer stitches on the back of the fabric and very small stitches on the top, you won’t see much stitching on the front of your fabric. This is called a hidden stitch. This is a good stitch to learn because we can use it for many of our wearable designs and sewing projects. The underside of a hidden stitch is shown in the following photograph:

Figure 2.42 – The underside of a hidden stitch

You can do any stitch you want, and often, using a nice color thread can add to the design. If you don’t want the stitch to show, then use a hidden stitch.

4. Protect the knots at the ends by dabbing a little nail polish onto them. Trim the ends so that we don’t cause any shorts in our circuit.
5. Let’s do the same again, but this time, on the negative or ground side.

Start at the lower LED sew tab, and sew all the way up to the next LED and then the next. Continue to the snap and sew it in place with several stitches.

6. When you have finished sewing, test whether your circuit works by snapping it together, as shown in the following photograph:

Figure 2.43 – Circuit testing

We tested the circuit earlier, so it should work at this point, too. Now with the LEDs on, you can finish sewing it into the wearable that you want to make.

Finishing your soft circuit

As I mentioned earlier, I have a vest that I’m adding this circuit to. Now that the circuit is finished, I’ll put it in place, and using regular thread, I’ll sew it to my garment. I’ll use the hidden stitch again so that the stitching will show on the back but not on the front.

The finished modification to the vest is shown in the following photographs. You can see the hidden stitch that is on the underside of the vest, and the front of the vest is pictured up close so that you can see the 3-LED detail in the circuit. Lastly, the completed vest is shown from further away so that you can see how it has been placed onto the vest:

Figure 2.44 – The finished LED circuit on the garment

So, you have created a circuit and sewn it into an item you already have, or made it into a bracelet or even a light for your bag. Now that the circuit has been completed, you’ll notice that we used snaps as a switch so that we can turn it on and off easily. We don’t need to remove the battery to turn it on or off. So, what is a switch and how is it used?

Using switches and buttons will add a lot more interaction to your wearables – it’s essential! So, let’s head to the next section, which is all about switches and buttons, where you will be creating your own switches to integrate into your wearables. Let’s jump right in to learn all about switches and buttons and also make some of our own!

Switches and buttons

Switches are breaks in your circuit that stop the current from flowing. In this section, we will learn about the various types of switches and buttons and how they work. Then, we will get creative and make our own switches.

In this section, I’ve included buttons. Although not strictly a switch, they also create a break in the circuit. We can use buttons and switches in similar ways. Figure 2.45 is a photograph of some of the types of switches and buttons that are available. However, bear in mind that there are hundreds of varieties, colors, sizes, and more.

Note that only a small selection has been pictured, so always go hunting for new and unusual items for your own wearable projects:

Figure 2.45 – Switches and buttons

First, let’s look at some of the types of switches we can use. The switches fall into two distinct categories, momentary and maintained. A momentary switch holds the connection for as long as the switch is held down. The maintained switch will hold the selection until it is deselected or switched in the opposite way. Let’s take a closer look at the following:

• Momentary switches
• Maintained switches

To understand momentary and maintained switches, let’s learn how a button or switch works. A break in a circuit is needed for a switch or button to provide the bridge or connection across the break. In Figure 2.46, you can see a button creating a break in the circuit to stop the LED from working. The schematic is also shown with a switch. This schematic is similar to our sewable snap and LED circuit:

Figure 2.46 – Schematic of a button and a switch closing the circuit

When the switch is closed, it completes the circuit. This allows the current to flow through the entire circuit. The LED will light up. The switch and button have two possible states: on and off or high and low.

Momentary switches

This is a switch that will change state while you hold it. When you are actively engaging the switch, it will be on or off. Then, when you release it, it will go back to its original state. Momentary switches can be normally open (NO) or normally closed (NC). This describes the default state for the switch. If the momentary switch is NC, then pressing it will open it, stopping the current in your circuit. If you’ve ever set the time on a cooker or watch, often, there are buttons that will count the time while you hold it. It will stop the time when you let go of the button. This is what a momentary switch will do. Another good example of this is a keyboard.

Maintained switches

This is a switch that holds its state until it changes into a new state. So, clicking on a button will activate it, and only when you click on it again, will it change state. One example is turning a desk lamp on, as the lamp will stay on until you turn it off.

Now that we understand the differences between a momentary (held for a moment) and a maintained (maintains the hold) type of switch and button, let’s look at how these switches and buttons are often categorized.

Don’t forget – the basis of all these buttons and switches is that there is an incomplete or opened circuit that will become complete or closed.

Example switches and buttons

Now, let’s take a look at a few switches and buttons that can be either one of the two overarching types we just discussed.

Latching buttons

A latching button is an on-off switch that stays on or off with a press. When you press it, it will stay on. This can be a good choice for a wearable to make it easy for the wearer to turn the circuit on or off. This is a type of maintained switch because the latch is physically clicked on and locked into place or out of place. These can be very satisfying to click and, typically, have a great “click” sound.

Toggle switches

Typically, this is a switch that has a lever, so it might not be very comfortable if you haven’t planned it into your circuit well. The toggle can stick out, so be sure to check the size when ordering. However, you can get really cute smaller ones. Making a forearm glove piece can suit it well. This is also a maintained switch.

Poles and throws

Some switches are called single-pole, single-throw (SPST) or single-pole, double-throw (SPDT). They refer to poles and throws. In Figure 2.47, we can see the schematic of an SPDT switch:

Figure 2.47 – Schematic of an SPDT switch

The pole is the number of circuits controlled by the switch, and the throw is how many positions the pole can connect to. Looking at the schematic, the SPDT switch has two possible ways to close the circuit. For example, if the switch is switched to the first throw, the LED in the bottom circuit will light up, and the other LED will be off. If the switch is thrown to the other circuit, this will be reversed. You don’t have to use both throws; you can use it as an on-off switch – just don’t connect anything to the other throw. That would mean you are using it as an SPST switch.

Slide switch

These can be very small and good in wearable designs. You slide them to create or break the connection. For example, underneath my mouse, there is an on-off slide switch.

Tilt switch

A tilt switch is an interesting switch. A tilt is opened or closed depending on how it is tilted. Mostly, it senses through a small metal ball that is located inside the switch. They can be very small.

Touch

Some buttons and sensors work on capacitive sensing and the signal that happens when you make contact. Often, these are standalone, momentary switches.

Other ways to use switches and buttons

We will explore touch capacity with certain circuit boards, or you can purchase a special touch sensor input board. When we look ahead to Chapter 7, Moving forward with Circuit Design Using ESP32, we will be using the input capacities of that board to work with touch.

There is a huge variety of switches and buttons available. I would suggest having a good hunt online, or finding a local electronics store, to see what fun components you can find. Some have LEDs in them or are very small and discreet – great for wearables – and some are very durable for more heavy-duty needs such as on a bag or backpack.

Now that we’ve gained an understanding of switches and buttons, the fun can begin. Let’s look at alternative materials that we can use and jump into making our own.

Activity 2.6 – making your own switches

There is an endless list of materials and objects we can use to make our own buttons and switches. Now that we understand how a switch creates a break in the circuit (and then completes it again), we can get creative:

Figure 2.48 – Materials to make buttons

Most of the materials in Figure 2.48 are from Adafruit, Tinker Tailor, or Proto-Pic, but there are also unusual items or household items. The small metal bee is used to decorate things; for example, I put them on purses. The silver studs go on the bottom of handbags as small feet, but they are metal, so you could use them creatively. This is the same for the stag head, which is used as a bag clasp. This is to illustrate that you should keep your eyes open to all the possibilities around you. You can even bring your multimeter to a haberdashery store!

Using the example of an LED, let’s look at how we can create different switches and buttons. We’ve already learned how to use sewing snaps to create a break in our circuit, so let’s see what we can do with the following:

• Conductive fabrics
• Hook and loop fasteners
• Zippers
• Copper tape/nylon tape

Using your multimeter, test the conductivity of materials around the home and see what you can find that could also be used for circuits. Do you have paper clips or pipe cleaners?

Conductive fabrics

Using conductive fabrics is a great way to make a switch. When the fabrics touch each other, a connection is formed. When they aren’t touching, the circuit will be off. Figure 2.49 shows the materials you need; three pieces of fabric work best. Here, I’ve used felt:

1. Using two pieces of conductive fabric, place them on another two pieces of fabric.
2. Cut out a shape on the third piece of fabric. Put that piece of fabric, with a pattern cut out (I’ve cut a heart), on top (Figure 2.49) of the conductive material:

Figure 2.49 – The fabrics needed, including layering fabric

3. The conductive material will be sandwiched between the two pieces of regular material (felt). This will allow you to actively press the button to get it to work.

Putting the pieces together, you should have the following:

• A piece of felt on the bottom
• A layer of conductive fabric
• A layer of felt with the cut-out shape in its center
• A layer of conductive fabric
• A piece of felt on the top

4. Sew your conductive thread to the top and bottom of your button to add them to your circuit. Be sure the conductive thread is sewn into the conductive fabric on one side, then sew into the conductive fabric on the other side (top and bottom of your button).

Remember, it is about making a break in the circuit, so it will be sewn into where the break will happen (Figure 2.50); for example, just like the snaps we sewed earlier:

Figure 2.50 – Felt, conductive fabric, felt with the heart shape cut out (left), then felt on the bottom and conductive fabric on top (right)

When you press this button together, the conductive fabric, which is only separated by that felt layer, will touch, completing the circuit. You can now make your own buttons and use them in your circuits to suit the body parts you are working on.

Another way to use conductive fabric as a switch is to sew it onto your wearable and then touch them together to close the circuit.

I made a glove out of felt and jersey fabric, and then sewed in some LEDs that were pre-mounted on long wires. I used conductive fabric on the thumb and pinky finger. This forms a connection, so when the thumb and pinky touch, it illuminates the lights.

These LED are also multicolor, so they switch between different colors the longer the connection is held in place. Figure 2.51 shows the conductive fabric and how it works:

Figure 2.51 – Tri-color LED glove with conductive fabric sewn onto the pinky and thumb pieces to create a switch

The preceding glove is just one example of using conductive fabric as a switch for your wearable. Think about where else you might incorporate a switch you can make. Spend some time sketching ideas, as you might use them for future projects!

Sometimes, when making simple sewable circuits, we use a battery holder, as we did in our first circuits. But what if you don’t have one? We can use conductive fabrics to make our own.

Need a battery holder? You can make one!

This is another perk of having conductive fabric in your wearables project box. Conductive fabric can save you from running out of a battery holder. This can be used in the circuit easily and more discreetly.

For the following circuit, you’ll need fabric, conductive thread, and conductive fabric (Figure 2.52):

Figure 2.52 – Battery holder items

With the conductive thread, sew a knot where you want the battery (negative side down) to go.

Make sure you have a big strong knot and sew over it a few times. Figure 2.53 shows the knot on the reverse side of the fabric, after you have sewn through the conductive fabric (bottom layer).

The top piece of the battery holder has a square of conductive fabric under the blue felt square (shown on the right), which will be the positive side of the battery holder:

Figure 2.53 – Making a battery holder

Then, you can slide your battery into the pocket you made. This is a quick circuit that you can sew into your wearable design.

Hook and loop fasteners

Conductive hook and loop fasteners are a good way to get a switch working. Sew your power to the hook side from your battery power side. Then, sew the loop side to the power side of your LEDs. When the hook and loop touch, it will complete the circuit, and they will light up. In Figure 2.54, the circuit connects with a hook and loop fastener:

Figure 2.54 – The hook on one side and the loop underneath

Zippers

We could use metal or plastic zippers, but they will make a difference to the type of switch we use. If it’s plastic, it will only connect exactly where the zipper bridges the connection. This creates a momentary switch. If you hold the zipper there, then it will maintain this bridge and keep the circuit on. I have made an example cuff piece. It has conductive thread high up where the zipper finishes. When you zip to that part of the zipper, it will keep a light on.

I used a cool light, which is a mock Edison filament. Normally, this is used as filament in a light bulb. They are made up of small LEDs in a row, so they look great! You can buy different lengths and colors. Be sure to get the 3V version for our wearable projects so that we can power it.

These can be purchased from: https://www.tinkertailor.tech/product-page/led-filament-strips

This example is running off a coin cell. The filament has a positive side and a negative side just like the LEDs we’ve been using. To make this fun project, thread your needle with conductive thread and sew your battery holder.

Create a conductive thread stitch from the positive side of your battery holder to one side of your zipper (Figure 2.55):

Figure 2.55 – Stitching from the battery holder

Sew very close to the zipper, and check that you can still pull the zipper over the conductive thread. Once you have a tight connection, sew back a stitch or two and knot (Figure 2.56):

Figure 2.56 – Sewing up to the zipper

To add the filament, we need to push the end through the fabric. Poke a hole into the fabric to push the end of the filament through to the underside. When it has been pushed through (Figure 2.57), sew conductive thread over it several times to make a knot:

Figure 2.57 – Filament through the fabric

Make sure to test that your zipper can still go over the zipper teeth. Figure 2.58 shows the zipper opened and closed, including the final working wearable glow cuff:

Figure 2.58 – Zipper working over the thread, and final glow cuff

When you pull your zipper up to that conductive thread connection, it will light. You can use this technique anywhere you’d like a zipper in a circuit. It’s an alternative switch!

Copper tape/conductive nylon tape

When mapping out a circuit, you can use copper tape or conductive nylon tape. Figure 2.59 shows conductive nylon tape:

Figure 2.59 – Conductive nylon tape

Conductive nylon tape can be purchased in different widths. This one from Adafruit is great at working the first time and with no overlap. This simple circuit works perfectly the first time, and the tape is a lot more flexible than copper tape. If you fold the tape back on itself, you can also create a switch that works to turn the LED on or off.

Copper tape can be a quick way to work out your traces and see which might overlap. It will help with planning. It isn’t as flexible as the nylon tape. In Figure 2.60, the track uses copper tape. Sometimes, you will need to layer it up when you change direction, and it can take some pressing to be sure you have a conductive track. Most copper tape has a non-conductive glue on the underside:

Figure 2.60 – Copper tape with a switch

Another good thing about using copper tape is that you can also solder wires to it.

Other random items

Always be on the lookout for random items that you can use to complete your wearable. Unique items can make a very creative circuit and an eye-catching design. Keep on the lookout for safety pins, foil, magnetic snaps, hooks and clasps, jewelry, pipe cleaners (with some of the “fuzz” scraped off), and other unique items made of metal.

Also, going to your local charity shop can be a great way to grab some bargains and be sustainable. There might be items with zippers, clasps, and similar that you can upcycle or practice your wearable journey on. I found these amazing snaps and hooks and eyes (Figure 2.61), which must be decades old but will work fine:

Figure 2.61 – Bargains from a charity shop

Being aware of other interesting items you can use for your wearables will keep it interesting, exciting, and unusual!

Summary

What an amazing journey you’ve just completed in this chapter. We went from learning about the basics of electricity to making simple circuits, to understanding how we can make our own buttons and switches. You used crocodile clips, breadboards, and conductive fabrics. I hope you tried the activities and made notes of circuits that you’d like to make in the future. Practicing these skills is a creative and rewarding experience.

The components used in this chapter can be found at http://www.adafruit.com, http://tinkertailor.tech, and http://www.proto-pic.co.uk.

Now we look forward to learning about e-textile toolkits. These are microcontroller boards and components made for creating wearable projects. They are different from a standard rectangular Arduino board, but we can still use Arduino to program them. All the knowledge from the upcoming chapter will help you to build upon the skillset you’ve just acquired and help us to create more complex and interactive wearable solutions.

Review questions and exercises

To help with your learning, try to answer the following review questions:

1. Try swapping the resistors in your LED circuit. How do 220-Ohm, 330-Ohm, and 550-Ohm resistors affect the circuit? What have you observed?
2. What are the two types of circuits that we looked at?
3. What is the difference between a closed circuit and an open circuit?
4. How would you wire a parallel circuit?
5. What are some advantages of making a soft circuit?
6. What are conductive materials and how do you know they are conductive?
7. Create a parallel circuit and a circuit in series using crocodile clips or a breadboard.
8. Create some sketches and notes for creative buttons and switches you can make. Take inspiration around you and draw some ideas out. This will be very useful later or if you’re struggling to think of ways to create your circuits.