Fabric Sensor: Soft Sensor

(link to our past documentation of this project)

(code for this project can be found here)

We designed a fabric sensor intended for the user to take one-word notes and send said notes as reminders to themselves.

Our primary purpose in creating this sensor was to write reminders on a device without the rigidity found in most devices offering the same service.

What our project actually ended up being was an exploration in soft wearables and sensing.
We discovered that the reason soft wearables are not the first choice of many is because the margin for error is so much smaller when dealing with dynamic material.

We also discovered several key aspects of creating soft touch pads. Most importantly is the overall construction. To sense position, we used three layers of material:

• conductive fabric (grounded)
• a spacing mesh
• a piece of velostat (with 4 connections to measure resistance)

By pressing on the fabric, a connection is made between the conductive fabric and a point on the velostat. The resistance from each measurement point to the point of contact is then measured with an ADC.

We experimented with several conductive fabrics, spacing meshes, and connection orientations. Our process can be found in our previous documentation (linked above).

Also, the xy data from the sensor needs to be linearized. The linearization method depends on the orientation of the connections, but for our final prototype we linearized using the catenery curve (http://forum.arduino.cc/index.php?topic=184285.0).

plan for information flow with the sensor

hypothetical layout of the sensor

rudimentary visual prototype

visual prototype in use

visual prototype in use

visual prototype in use

sewing conductive fabric to make the buttons

sewing wires attached to conductive fabric buttons

sewing the arm straps on and defining the sensing area

inner velostat hand-sewn (because we were afraid that the sewing machine would rip through the velostat given its thickness), wires at four corners with copper tape on ends, 

light blue bean, with wires soldered to it to connect it to the ADS 1015 Breakout to give us four analog breakout pins instead of two, which are how many are available on the light blue bean

testing the sensor with visual output in Processing

circuit diagram of our ADS 1015 Breakout to light blue bean

YouTube / Rachel N – via Iframely

getting the light blue bean’s accelerometer data

YouTube / Rachel N – via Iframely

testing in progress

Final project:

in off mode; no LED on

on, as indicated by red LED. ready to write.

simple controls to decide when we start, end, and give ourselves reminders

light blue bean circuitry and wires hidden under fabric flap!

YouTube / Rachel N – via Iframely