Todd Wolfson

Software Engineer

October 24, 2019

As part of building Cone Down, one of our features was making the dancefloor interactive. We went with pressure sensitivity, built a prototype, but ran into 2 snags that stopped us:

  • We ran out of time (e.g. assembly, debugging)
  • Dancefloor cover (polycarbonate sheet) warped under heat (discovered at Burning Man) thus further iteration became implausible at the event

Here's the final functional setup we used for our top-of-frame prototype (polycarbonate unmounted in photo):

Prototype photo

Dancefloor sensor layout

This is a layout for 1 of the 9 tiles dancefloor. Inside of each tile is a small 3x3 grid for supporting polycarbonate which can be bendy

The 4 sensors in place will detect the "+" sign shape for the dancefloor tile. We settled on this approach as it's much more economical than the full square which requires double the cost

Each sensor was a force sensitive resistor using a secondary static resistor to create a voltage divider circuit. Surprisingly similar to this:

https://learn.sparkfun.com/tutorials/force-sensitive-resistor-hookup-guide#example-hardware-hookup

For pressure detection/keeping the sensors in place, each sensor had a mounting tape square underneath and we used bumpons to distribute the load from the weight of the polycarbonate

Items used:

Here's a high level rundown of our process:

  • Considered many types of sensors sold by Adafruit and SparkFun (e.g. light, sound, pressure, flex)
  • Went with force sensitive resistor as it:
    • Doesn't break under heavy weights (e.g. accidental art car on platform)
    • Won't have light/sound transmission issues
    • Easy to wire up (only need power and ground)
    • In hindsight, we should have explored flat switch membranes but we had too little time when the suggestion came up
  • Set up test with Arduino, force sensitive resistors (FSR), and 50' of 22AWG cable round trip (not in setup/photo yet) (dancefloor was 12'x12', thus at most 24' there and 24' back) Arduino and sensor test
  • Iterated with FSR on small wooden box
    • Using FSR taped down didn't work
    • Added charger cord on top of FSR to test focused pressure, this worked
    • Key is to have material which deforms earlier than polycarbonate
    • On a later date, we formalized this to a bumpon and verified it works once again Small tile with bumpon layout
  • Made large scale prototype for 1 dancefloor tile
    • Sensors didn't stay in place with tape, also broke easily
    • Added mounting tape to bottom of sensors, worked great
    • Got lots of false positives due to mounting tape oversticking polycarbonate at times
    • Explored a few configurations (e.g. corners of tile, bumpons next to sensors, caulked down polycarbonate) Prototype with sensors in corners Sensor with bumpons adjacent
    • Concluded that ideal setup is: sensors on edges of inner 3x3 with bumpons next to sensors Final prototype
  • Started building cables and bought full sensor order for on-playa installation but ran out of time

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