File: src/io/Servo.js

/**
 * Based on Servo.as originally written in as3.
 * Copyright (c) the Funnel development team
 * http://www.funnel.cc
 *
 * Ported to JavaScript by Jeff Hoefs
 * Copyright (c) 2011-2012 Jeff Hoefs <soundanalogous@gmail.com>
 *
 * Released under the MIT license. See LICENSE file for details.
 */

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

BO.io.Servo = (function() {

  var Servo;

  // dependencies
  var Pin = BO.Pin;

  /**
   * Creates an interface to a Servo motor. Use this object to set
   * the angle of the servo head. You can simply specify and angle between
   * 0 and 180 degrees and the servo head will rotate to that angle. See
   * [Breakout/examples/actuators/servo.html](https://github.com/soundanalogous/Breakout/blob/master/examples/actuators/servo.html) for an example application.
   * You can also use this with a continuous rotation servo. See the
   * description for the angle property for use with a continuous rotation
   * servo.
   *
   * @class Servo
   * @constructor
   * @param {IOBoard} board A reference to the IOBoard instance that the
   * servo is attached to.
   * @param {Pin} servoPin A reference to the Pin the servo is connected to.
   * @param {Number} minAngle The minimum angle the server can rotate to
   * (default = 0).
   * @param {Number} maxAngle The maximum angle the server can rotate to
   * (default = 180).
   */
  Servo = function(board, servoPin, minAngle, maxAngle) {
    "use strict";

    this.name = "Servo";

    this._pin = servoPin;
    this._angle = undefined;
    this._minAngle = minAngle || 0;
    this._maxAngle = maxAngle || 180;

    var pinNumber = servoPin.number;

    // sendServoAttach will set the pin mode to Pin.SERVO
    board.sendServoAttach(pinNumber);
  };

  Servo.prototype = {

    constructor: Servo,

    /**
     * Set the angle (in degrees) to rotate the server head to.
     *
     * <p>If you are using a continuous rotation servo, a value of 90
     * will stop the servo. A value of 0 (or < 90 depending on the servo)
     * will cause continous clockwise rotation and a value of 180 (or > 90)
     * will cause continuous counter-clockwise rotation. If your motor
     * does not come to a full stop when setting 90 degrees, you will need
     * to adjust the servo (there is typically a screw on the motor) to
     * adjust</p>
     *
     * @property angle
     * @type Number
     */
    set angle(value) {
      if (this._pin.getType() === Pin.SERVO) {
        this._angle = value;
        //this._pin.value = this._angle;
        this._pin.value = Math.max(0, Math.min(1, (this._angle - this._minAngle) /
          (this._maxAngle - this._minAngle) * Servo.COEF_TO_0_180));

      }
    },
    get angle() {
      if (this._pin.getType() === Pin.SERVO) {
        return this._angle;
      }
    }
  };

  /**
   * The scale to convert 0-1 (0-255 in 8bit) to 0-0.706 (0-180 in 8bit).
   * @property Servo.COEF_TO_0_180
   * @static
   */
  Servo.COEF_TO_0_180 = 180 / 255;

  return Servo;

}());