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  • A few people have asked about having an accelerometer so they can detect movement - but it's not the only way.

    For a lot of things you can still use the magnetometer. The magnetic field changes a lot, not just with angle, but with what other items the Puck.js is near. It's almost impossible to move Puck.js without changing the magnetometer's reading at least a little.

    For instance try this code:

    var avr = Puck.mag();
    var magDiff;
    Puck.on('mag', function(xyz) {
      // work out difference in field
      var dx = xyz.x-avr.x;
      var dy = xyz.y-avr.y;
      var dz = xyz.z-avr.z;
      magDiff = Math.sqrt(dx*dx+dy*dy+dz*dz);
      // update average
      avr.x += dx/2;
      avr.y += dy/2;
      avr.z += dz/2;  
      LED.write(magDiff > 50);

    It looks for changes in the magnetic field about once a second, and will light the red LED if it has changed more than a little. After a few seconds of no movement the LED will turn off.

    It's easy, low power, and seems to work pretty well.


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