Materials (touch sensing)

The interactions with the Peabody quilt are touch based – the user presses on a square and the LED lights up. Thus, parts of the quilt must be sensitive to touch. There are two potential ways to include touch sensitivity in the quilt: pressure sensors or capacitive touch.

Capacitive touch sensing is a type of sensing that doesn’t require much force, if any, to trigger. Any conductive material can be a capacitive touch sensor. You just need to add power, a resistor and your touch! Here’s a great video that explains the physics behind capacitive touch:

Why capacitive touch?

  • avoids unnecessary roughness with the quilt (in an extreme example, you don’t even have to touch it if you have a strong enough resistor)
  • can work with conductive fabric so the quilt itself can be the sensor
  • can detect touch through any insulating material (like the LED’s silicone casing) which would allow us to conceal a sensor if needed
  • each sensor only needs one wire
  • relatively inexpensive (cheaper to buy conductive fabric and cut it than to buy 900 pressure sensors)
  • there is an existing capacitive touch sense library for arduino

Potential Material for the capacitive sensor

  • conductive fabric (knitted superlight conductive fabric is transparent to allow the LED to shine through)
  • silver ink (the ink could be painted in a circle on the quilt around the LED so as not to block the light)

Things to consider with capacitive sensing

  • LED must be able to shine through the quilt
  • the quilt cannot be used if it is laying on a metal or static dissipative surface. The capacitive touch-sensing circuit must be insulated
  • the resistor value affects the sensitivity of the touch sensor– at the low end (1 mega-ohm) the sensor will only be activated by absolute touch, and on the high end the sensor can be activated from a distance of 12 inches or more
  • each sensor requires one wire which means there will be 900 wires running through the quilt. A possible solution is to 900 pieces of conductive thread that go to a central exit point on the quilt connecting to actual wires