So, your circuit is working and you are ready to go to the next step in the prototyping phase- getting the circuit onto fabric. Your circuit will be clipped together with alligator leads at this point. Or you may have a breadboard in use or you may have both alligator leads and a breadboard. You have also been using the computer for power through the USB port while you have you testing and uploading your sketches.
You should have a piece of fabric or sewn pattern ready for the circuit. Now is the time to combine the two and put the circuit onto the fabric. This process comes with valuable challenges while also making use of learned techniques.
Now is the time to combine the two and put the circuit onto the fabric. This process comes with valuable challenges while also making use of learned techniques.
1) Record Circuit
After the final circuit is built and tested with the sketch, it is ready to transfer onto fabric. To do this, the circuit needs to be unclipped and taken apart. To know how to put the circuit back together it needs to be recorded. There are three ways you can do this that I will briefly go over now:
1) Draw a schematic diagram. I find this to be a fun process because learning how to read schematics is like learning how to decode secret messages coupled with reading a map. In a schematic diagram, each electrical component is represented by a graphic symbol. Check out this instructable of How to Read Circuit Diagrams for an introduction to schematic symbols. The Electronic Symbol page on Wikipedia is also a good place to start.
2) Create your own drawing. Use a pencil or computer to create a diagram of your own making. Mark the pin numbers on the microcontroller and the power and ground of each component. Draw in the traces and you have your own roadmap of which to rebuild your circuit by.
3) Write it down. For simple circuits, you can write down each connection line-by-line. For example:
Switch –> pin 2
Switch –> ground
LED power (+) –> pin 3
LED ground (-) –> ground
You can also use Fritzing, a software that lets you make circuit diagrams using graphics of the components. Double check the circuit with what you recorded before taking it apart.
Once you have recorded the circuit, you are ready to safely take the circuit off the alligator leads and the breadboard.
3) Place Components
Place the components on top of the fabric to see how they all lay in relation to one another. Take a moment to finalize where the components and microcontroller will be.
Things to take into consideration when placing your components:
1) Visualize your conductive paths. When possible, do not put a component in a place that will create paths that cross one another.
2) Leave room to sew down and around components
3) Are any components polarized?
Use chalk or a disappearing ink pen so you can draw the placement and circuit as many times as you like.
Below are topics pertaining to the user experience, with examples of how these topics apply.
- will the microcontroller inhibit wrist movement if I place it on the wrist?
- will the user be able to reach the button or see the LED?
Balance (with larger piece of fabric and heavy components)
- will the weight of my battery interfere with the drape of my fabric?
- does the arrangement fit my aesthetic standards and communicate what I need to the user?
When placing components, keep these things in mind as a good practice.
- Place your components so the pads that need to connect can access each other easily and without crossing too many other conductive paths.
- Figure out where the battery will go and how it will connect to the microcontroller, it can easy to forget about when developing the circuit while connected to the computer.
- Your power and ground lines between the battery and circuit want to be as short as possible if using conductive thread. Why? Because conductive thread has resistance and adds up over distance. Imagine if you have an LED connected to the battery, the battery is on your hip and the LED is on your ankle and they are connected by conductive thread. The battery is 3v and the LED is rated as needing 2.8 – 3 volts to operate. Some conductive thread has a resistance of 14 ohms per foot, let’s say you used a zigzag stitch down the leg, totaling about 4 feet of thread between the battery and LED. Four feet of the thread equals 56 ohms, the LED may be dimmed by this, or cause it to not light at all. This can also take away some current you will need for the rest of the circuit.
4) Trace Components
5) Draw in Circuit
Refer to the connections you recorded before you took everything off the alligator leads.
Start to draw in each connection.
Notice how the traces going from LED ground and power pin to the microcontroller pins are going within the boards ouline. This means the traces will be under the board.
Under the microcontroller or a component can offer you more real estate for your traces. Just beware of creating a short circuit. The conductive thread or fabric may touch two open metal spots on the bottom of the board, causing a short. Double check to see if there is danger of that before drawing and making your trace.
Build Circuit on Fabric
To build your circuit on fabric, you have a choice of some soft conductive materials. The two you will be choosing from are conductive thread and conductive fabric. Read below for more info on either one. The thread gets sewn into the fabric, the fabric get’s ironed on. Immediately below you will see examples of a sewn conductive thread circuit.
Secure and Trim
Cut off tails and secure knots on the underside. Also, anywhere it will touch the skin, cover any exposed conductive thread, using more fabric or fusible interfacing. Skin is conductive too and gets even more so when a person perspires.
Use fabric glue on and around each knot to secure.
Test all your sewn and ironed connections with a multimeter. The number one reason a circuit does not work is because a connection is broken or has broken over time. Make them strong and think about strain relief!
Sewing a Circuit
The Uneven Running Stitch
This stitch is the same as the running stitch except every other stitch is shorter than the other. I find it useful in wearable electronics when I want to minimize the amount of conductive thread exposed on one side. This side is usually the inside of a garment or accessory that touches the skin.
If you are working with fabric that has some thickness, like the felt, the exposure can be minimized further by only picking up the top of the fabric as you make the shorter stitch.
So far, you have used conductive fabric to build switches with, but conductive fabric is great for other things, such as building entire circuits!
Like the fabric you find in a fabric store, conductive fabric comes in different weights and can be a woven or a knit. You can check out all the conductive fabric they sell at lessemf.com. In this class, you use Shieldit, a conductive fabric that comes with a polymer coating on one side. This coating melts under high heat, making it capable of being ironed onto a fabric and great for quickly building circuits.
Conductive thread can still be used to build entire circuits with, but it has more of a potential of creating shorts due to its hairy nature. It also has a higher electrical resistance and takes much longer to sew a circuit versus ironing down strips of fabric.
Just like conductive thread fabric has the same disadvantage of being uninsulated. This can be remedied in several different ways. You can use other iron-on fabrics, polymer coatings and even thread using embroidery techniques. In this class, you will learn how to insulate using iron-on fabric. To dive deeper on how to use conductive fabric using techniques outside of this class, check out my How to Work With Conductive Fabric instructable.
Cut some thin strips of conductive fabric to prep for the circuit. Cut more than you need, they come in handy as you build. You can also use the Silhouette CNC cutting machine.
Use the Silhoutte Cameo a CNC cutting machine! Read an Instructable to learn how to cut a circuit on the Silhouette.
Lay Down Circuit
Start laying down the conductive fabric strips and cutting to length. To make an electrical connection and add length to a trace create an overlap.
Heat your iron to a mid-high setting, somewhere around the wool mark. Start ironing the strips down, it’s best to do them one-by-one.
Sew Components Down
Sew your components down using conductive thread using small and tight stitches. Use at least 3 stitches.
Test all connections with a multimeter on continuity setting!