School of Maaa Day 3 - Capacitive Sensing

School of Maaa Day 3 - Capacitive Sensing

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Becky Stewart

August 15, 2014
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  1. Capacitive Sensing

  2. Bitlace: For Richard Hannah Perner-Wilson http://etextile-summercamp.org/swatch-exchange/bitlace/

  3. Bare Conductive Touch Board http://www.bareconductive.com

  4. http://playground.arduino.cc/Main/CapacitiveSensor Capacitive Sensing

  5. Arduino Send Pin Arduino Receive Pin very large value resistors

    work best (100k to 50M) object used as sensor Capacitive Sensing
  6. signal is sent out a pin object used as sensor

    Capacitive Sensing
  7. signal is sent out a pin wait for second pin

    to match that signal object used as sensor Capacitive Sensing
  8. small capacitor can help smooth and stabilise output object used

    as sensor Capacitive Sensing Arduino Send Pin Arduino Receive Pin
  9. object used as sensor can add a smaller value resistor

    (1k is fine) to protect the receive pin from something like a static electricity shock Capacitive Sensing Arduino Send Pin Arduino Receive Pin
  10. Capacitive Sensing object used as sensor 1 Arduino Send Pin

    Arduino Receive Pin 1 object used as sensor 2 Arduino Receive Pin 2
  11. Capacitive Sensing Tips for choosing a resistor ! (from library

    documentation) • 1 megohm resistor (or less maybe) for absolute touch to activate. • 10 megohm resistor the sensor will start to respond 4-6 inches away. • 40 megohm resistor the sensor will start to respond 12-24 inches away (dependent on the foil size). Common resistor sizes usually end at 10 megohm so you may have to solder four 10 megohm resistors end to end. • One tradeoff with larger resistors is that the sensor's increased sensitivity means that it is slower. Also if the sensor is exposed metal, it is possible that the send pin will never be able to force a change in the receive (sensor) pin, and the sensor will timeout.
  12. Capacitive Sensing This entire circuit is based on a common

    ground!! ! Arduinos not plugs into mains power may have problems! ACHTUNG!
  13. Challenge Trigger 3 different outputs depending on the distance from

    a capacitive sensor.
  14. To Review…

  15. To Review… We’ve looked at 3 ways of creating sensors

    to input information from the real world into an Arduino: 1. Switches ! 2. Variable resistors ! 3. Capacitive sensors
  16. To Review… Switches:! • Cheap • No calibration • Very

    few components • Need to remember pull up and pull down resistors
  17. To Review… Variable Resistors:! • Ability to capture more subtle

    interactions • Requires calibration for meaningful input • Need to carefully choose other components in voltage divider circuit
  18. To Review… Capacitive Sensing:! • Ability to capture very subtle

    interactions • Sensor can be completely hidden from view • Requires lots of calibration for meaningful input • Batteries can cause unexpected problems!
  19. Challenge Go forth and make body-centric/wearable/soft circuit sensors!

  20. Becky Stewart http://theleadingzero.com becky@theleadingzero.com @theleadingzero