Detecting movement

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);
});
Puck.magOn();

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.