johnny-five/lib/ping.js

The JavaScript Arduino Programming Framework.

var Board = require("../lib/board.js"),
  events = require("events"),
  util = require("util"),
  within = require("./mixins/within"),
  __ = require("./fn");

/**
 * Ping
 * @param {Object} opts Options: pin
 */

function Ping(opts) {

  if (!(this instanceof Ping)) {
    return new Ping(opts);
  }

  var settings, last, samples, median;

  last = null;
  samples = [];

  // Initialize a Device instance on a Board
  Board.Device.call(
    this, opts = Board.Options(opts)
  );

  this.pin = opts && opts.pin || 7;

  // Ping instance properties
  //
  //
  this.freq = opts.freq || 100;
  // this.sensitivity
  this.pulse = opts.pulse || 500;

  this.microseconds = null;

  // Private settings object
  settings = {
    pin: this.pin,
    value: this.io.HIGH,
    pulseOut: 5
  };

  this.io.setMaxListeners(100);
  // Interval for polling pulse duration
  setInterval(function() {
    this.io.pulseIn(settings, function(duration) {

      this.microseconds = duration;
      samples.push(duration);

    }.bind(this));
  }.bind(this), this.pulse);

  // Interval for throttled event
  setInterval(function() {
    var err;

    err = null;

    median = samples.sort()[Math.floor(samples.length / 2)];

    if (!median) {
      median = last;
    }

    // @DEPRECATE
    this.emit("read", err, median);
    // The "read" event has been deprecated in
    // favor of a "data" event.
    this.emit("data", err, median);

    // If the median value for this interval is not the same as the
    // median value in the last interval, fire a "change" event.
    if (Board.range(last - 32, last + 32).indexOf(median) === -1) {
      this.emit("change", err, median);
    }

    // Store this media value for comparison
    // in next interval
    last = median;

    // Reset samples;
    samples.length = 0;
  }.bind(this), this.freq);


  Object.defineProperties(this, {
    // Based on the round trip travel time in microseconds,
    // Calculate the distance in inches and centimeters
    inches: {
      get: function() {
        return +(median / 74 / 2).toFixed(2);
      }
    },
    cm: {
      get: function() {
        return +(median / 29 / 2).toFixed(3);
      }
    }
  });
}

util.inherits(Ping, events.EventEmitter);
__.mixin(Ping.prototype, within);

module.exports = Ping;


//http://itp.nyu.edu/physcomp/Labs/Servo
//http://arduinobasics.blogspot.com/2011/05/arduino-uno-flex-sensor-and-leds.html
//http://protolab.pbworks.com/w/page/19403657/TutorialPings