Capacitive Wheel Fabric Sensor

In this Instructable I will be remaking the sensor you see above: a capacitive wheel sensor using bonded conductive fabrics. There is no sewing involved! The circuit itself is also super simple. Each piece of the sensor has one lead which connects to a microcontroller. Your finger acts as the ground and completes the circuit. That's it! Read more about capacitive sensing on Wikipedia

The sensor can be programmed to control anything you want. We are using the sensor as a volume wheel to control the feedback on a bodysuit with haptic motors and heating elements.

This sensor design is from a project called the Embodisuit, a collaboration between Rachel Freire and Sophia Brueckner made at Pier 9 during our Residency. The whole project will be open source and published online so follow us to see it progress. You can see Sophia's related Instructables on her page.

You can see more work-in-progress images here: https://www.flickr.com/photos/rachelfreirestudio/albums/72157681593397721

And images of the rest of the Embodisuit project here: https://www.flickr.com/photos/rachelfreirestudio/albums/72157683299162666

This sensor is made with stretch materials as part of my ongoing project Second Skin. There is an instructable about stretch circuits here. You can also make it from non-stretch material. See materials list in the next step.

Step 1: Materials and Tools

Tools:
- Fabric scissors
- paper scissors
- tiny scissors
- scalpel
- metal ruler
- grading ruler
- pins
- domestic iron or mini iron
- multimeter
- snap tool (optional, if you are using snaps)

Materials:
1. powernet (two weights: light and heavy. I have used white heavy powernet for the base of my sensor, and light ivory powernet for the optional top layer)
2. lycra or other thin, tightly woven material. I am using Eurojersey: http://www.sensitivefabrics.it/
3. conductive fabric Techniktex P130B: http://www.shopvtechtextiles.com/5195-Fabric-Samplers--_p_177.html
4. Bemis Sewfree stretch fusing: http://www.extremtextil.de/catalog/Sewfree-elastic-iron-on-adhesive-film-small-piece::1783.html *
- snaps: https://www.amazon.com/100-SETS-PRONG-FASTENERS-Pieces/dp/B0061B52FA (optional)

Microcontroller and electronics:
- Teensy 3.2 (the code in this Instructable is for teensy and it's dedicated touch pins)
- connectors from fabric to breadboard (e.g. straight pins with alligator clips, or etextile connectors you can make yourself, such as this)
- breadboard
- computer with Arduino and Teensyduino installed

All the materials listed here are stretch materials. But this sensor could also be made with non stretch materials and cheaper conductive materials such as:
1. denim, linen, silk, leather
2. dress lining or silk
3. conductive ripstop: https://www.lessemf.com/fabric4.html#1212
4. Heat N' Bond (US) or Bondaweb (EU) *

* IMPORTANT! The Bemis Sewfree bonding allows an electric current to pass through two materials when the bond is made. This is because it sinks into the fabric and allows it to touch and connect through the bond. If you use a different bonding material, first make a sample and test with a multimeter to make sure there is a stable connection

Step 2: Prepare Your Pattern

Download the PDF file and print three copies. Cut out as seen above:

1. leave complete, to use as a stencil under your fabric to lay the traces
2. stencil for the sensor wheel
3. placement of the through-hole connections from traces to sensor

Step 3: Making the Circuit

Prep:
Iron the fusing on to the conductive fabric and cut into strips. I find 7mm strips are the most reliable and also look good.

Traces:
Pin the pattern under your fabric to use as a stencil. Heat the iron for silk rather than to full power.

Peel the backing from the conductive strips and lightly iron into place making sure the traces don't touch.

The conductive fabric can be lightly tacked into place, just to melt the bonding material. I get my placement right, then put a pressing cloth over the whole circuit and apply pressure for 10-20 seconds to seal the traces in place.

Isolation:
Next make the isolation layer from a thin fabric. I have used Eurojersey lycra as it is super thin.

Bond a small swatch of lycra and trace your isolation layer, carefully cutting out the small circles for the traces to show though. These will be the connections to the sensor. Iron in place, making sure each hole lines up to a conductive trace.

Because this lycra circle isolates the traces under the sensor, this next part in brackets is optional. I am applying this layer to (1) isolate all the traces in my garment and (2) for aesthetic reasons.

[Use the pattern to trace the complete wheel and add a seam allowance of 5mm around the tracing. cut this larger shape out of fusing with the glue side facing down. Place the thin powernet over the top and bond to isolate all the traces.

Note in the images that I initially made this piece solid (because the bond should connect through the perforated mesh fabric), but I had to go back, heat the bonding material to delaminate it, and carefully remove the small circles to make my connections stable. It is definitely safer to trace the holes and cut them out! I've added this step for clarity because the isolated traces are visible in the final sensor]

Step 4: Making the Sensor and Continuity Testing

Sensor:
trace the sensor using the stencil and cut it out. Lay the pieces on the fabric, making sure each piece of the sensor connects to one of the through-holes and covers it completely. Make sure non of the pieces touch.

Tack with an iron and when the sensors are placed correctly, cover with a cloth and apply heat and pressure for 10-20 seconds.

Continuity test:
Test with a multimeter. I have used pins to pin though the fabric to connect to my isolated traces. You could also connect with safety pins. For an Instructable on safety pin connectors go here.

Step 5: Teensy 3.2 Microcontroller and Code

We are using a Teensy 3.2 as it has dedicated touch sensors for capacitive sensing.

We made connectors with safety pins on one end and header pins on the other to connect to a breadboard. This is because the traces are isolated. It can also be connected with alligator clips connecting to straight pins, in the same way the multimeter test was done.

Connect each of the sensor traces to one of the touch pins on the Teensy. We are using pins 15-19 and 22. there is no ground pin as your finger will act as the ground in this circuit.

Go to Sophia's Instructable to get the code and instructions explaining how to modify it for your own project. The Processing sketch makes it easy to see if your sensors are working.

Step 6: Finished Sensor!

The final sensor is in the front of our garment. It will be programmed to function as a volume scroll wheel to control sensations sent to the body by the motors/heaters on the spine.

it has small snaps to connect across the opening of the garment to the breakout board at the back. These snaps have teeth which pierce through the garment and this makes a good connection to the isolated traces in the same way as the pins do.

This was done as an exercise to test how well the snaps worked as both a garment fastener as well as a connector. Often wearable circuits are limited by garment configuration so this was a nice (although somewhat unnecessary) solution. As our garment develops and becomes more complex this connection solution will become an integral part of the design.