File: src/io/CompassHMC6352.js

/**
 * Copyright (c) 2011-2012 Jeff Hoefs <soundanalogous@gmail.com>
 * Released under the MIT license. See LICENSE file for details.
 */

JSUTILS.namespace('BO.io.CompassHMC6352');

BO.io.CompassHMC6352 = (function() {

  var CompassHMC6352;

  // dependencies
  var I2CBase = BO.I2CBase,
    CompassEvent = BO.io.CompassEvent;

  /**
   * Creates an interface to an HMC6352 Digital Compass module.
   * Use the compass to obtain a heading. You must hold the sensor flat
   * to obtain the most accurate heading value (just like an analog compass).
   * The compass is also useful in obtaining a rotation value in relation
   * to a fixed position. See [Breakout/examples/sensors/hmc6352.html](https://github.com/soundanalogous/Breakout/blob/master/examples/sensors/hmc6352.html) and
   * [Breakout/examples/processing\_js/compass.html](https://github.com/soundanalogous/Breakout/blob/master/examples/processing_js/compass.html) for example applications.
   *
   * @class CompassHMC6352
   * @constructor
   * @extends BO.I2CBase
   * @param {IOBoard} board The IOBoard instance
   * @param {Number} address The i2c address of the compass module
   */
  CompassHMC6352 = function(board, address) {

    address = address || 0x21;
    this._heading = 0;
    this._lastHeading = 0;

    this.name = "CompassHMC6352";

    I2CBase.call(this, board, address);

    // 0x51 = 10 Hz measurement rate, Query mode
    this.sendI2CRequest([I2CBase.WRITE, this.address, 0x47, 0x74, 0x51]);
    this.sendI2CRequest([I2CBase.WRITE, this.address, 0x41]);

    this.startReading();

  };

  CompassHMC6352.prototype = JSUTILS.inherit(I2CBase.prototype);
  CompassHMC6352.prototype.constructor = CompassHMC6352;

  /**
   * [read-only] The heading in degrees.
   * @property heading
   * @type Number
   */
  Object.defineProperty(CompassHMC6352.prototype, "heading", {
    get: function() {
      return this._heading;
    }
  });

  /**
   * @private
   * @method handleI2C
   */
  CompassHMC6352.prototype.handleI2C = function(data) {

    // data[0] = register
    this._heading = Math.floor(((data[1] << 8) | data[2]) / 10.0);

    if (this._heading != this._lastHeading) {
      this.dispatchEvent(new CompassEvent(CompassEvent.UPDATE));
    }
    this._lastHeading = this._heading;
  };

  /**
   * Start continuous reading of the sensor.
   * @method startReading
   */
  CompassHMC6352.prototype.startReading = function() {
    this.sendI2CRequest([I2CBase.READ_CONTINUOUS, this.address, 0x7F, 0x02]);
  };

  /**
   * Stop continuous reading of the sensor
   * @method stopReading
   */
  CompassHMC6352.prototype.stopReading = function() {
    this.sendI2CRequest([I2CBase.STOP_READING, this.address]);
  };


  // document events

  /**
   * The update event is dispatched when the compass heading is updated.
   * @type BO.io.CompassEvent.UPDATE
   * @event update
   * @param {BO.io.CompassHMC6352} target A reference to the CompassHMC6352 object.
   */

  return CompassHMC6352;

}());