Dawn's Soft Circuit Assignment: Rescue Bracelet

Due February 17, 2010

For the assignment to make a soft circuit input and output, I decided to make a touch sensor that lights up a light. Making such a circuit from flexible materials could be useful for integration of such circuits into comfortable clothing. I was living in New Zealand when the head of their national museum, Te Papa, was found dead after being caught in a snowstorm on a mountain. I'd like to think that having easy-to-use, comfortable emergency equipment or accessories could have helped rescuers find Dr. Bennington.

This bracelet is made from flexible neoprene. When the light area is pressed, the super-bright blue LED is illuminated.

The circuit part of the bracelet is between layers of neoprene near the snap joint of the bracelet.

To construct the fabric touch sensor, I used interfacing to attach two pieces of conductive fabric to a piece of neoprene with a hole cut out in the middle. Therefore, by pressing the neoprene-fabric sandwich, the two pieces of conductive fabric make contact with each other. This completes the circuit and lights the LED. The connections from the battery to the LED to the switch are all made using conductive thread which is sewn into the middle of the neoprene to reduce its degradation due to wear.

The circuit diagram of the bracelet is shown below.

Videos of the Rescue Bracelet in Action

http://web.mit.edu/dawn/www/MAS962/softsensor/Rescue_Bracelet.mov

http://www.youtube.com/watch?v=G62psCEd1O0

Thanks to Tony Yu for being my hand model.

Thoughts, Improvements, Suggestions

  • The touch sensor is very sensitive. I think the hole I cut in the neoprene is very large compared to what was needed. Also, if you bend the wristband too much, the fabric buckles and sometimes makes contact by itself through the hole in the neoprene.
  • Snaps are conductive. Next time I should put the snaps far away from the sensor so the snap edges don't accidently short the circuit around the sensor. Or I could use the snap's conductivity as another form of switch in future projects...
  • Blue LEDs are blinding. I need to find a way to diffuse the light for future projects. (Although for a rescue application, this directed bright light is a good thing.)