Thursday, March 14, 2013

Irrduino: A Sprinkler System Built Using Arduino, Android, Google App Engine, Python, and Dart

Cross-posted from Dart News & Updates.



Developers frequently ask me if Dart is ready for the real world. Well, of course, that depends on the application. Check out this short video in which Joe Fernandez and I not only show that Dart can be used in the real world, we also show that it can be used to take the tedium out of watering your lawn!



The Dart code for Lawnville was originally written in January of 2012, a mere three months after Dart was launched as a "technology preview". That was six months before Dart's M1 release, so it's been updated a few times along the way. However, the code really hasn't fundamentally changed that much since the beginning.

Perhaps the most interesting piece of code is the use of a Queue (from the dart:collection library) to schedule watering tasks. You can click on different parts of the lawn, and the droid will fly over and water each section for a short amount of time:
  _actionQueue = new Queue();
  ...
  _actionQueue.add({'action': 'water', 'zone': el.id});
  ...
  void _executeActionQueue() {
    if (_actionQueue.isEmpty) {
      _waitingForTimer = false;
      _idle();
    } else {
      var action = _actionQueue.removeFirst();
      _doAction(action);
      _waitingForTimer = true;
      new Timer(new Duration(milliseconds: TIMER_INTERVAL),
                _executeActionQueue);
    }
  }
A Timer and window.requestAnimationFrame are used to control animations:
  void _repositionDroid(int x, int y, [Callback callback = null]) {
    x -= (HALF * DROID_WIDTH).toInt();
    y -= DROID_HEIGHT;
    _droid.src = "/static/images/droid-jetpack-on-front.png";
    _droid.style.left = "${x}px";
    _droid.style.top = "${y}px";
    new Timer(new Duration(milliseconds: REPOSITION_DURATION), () {
      if (callback != null) {
        callback();
      } else {
        _droid.src = "/static/images/droid-waiting-front.png";
      }
    });
  }

  void _startAnimationLoop() {
    _animationStartTime = new DateTime.now().millisecondsSinceEpoch;
    window.requestAnimationFrame(_animationLoop);
  }

  void _animationLoop(int timestamp) {
    _animationProgress = timestamp - _animationStartTime;
    for (Callback callback in _animationCallbacks.values) {
      callback();
    }
    window.requestAnimationFrame(_animationLoop);
  }
An HttpRequest is used to send commands to IrrduinoServer which in turn sends commands to IrrduinoController in order to control the sprinkler system:
  void _waterRpc(int zone) {
    var req = new HttpRequest();
    int secs = (TIMER_INTERVAL * SECS_PER_MS).toInt();
    req.open("POST", "/?water-zone=true&zone=${zone}&secs=${secs}", true);
    req.onReadyStateChange.listen((Event e) {
      if (req.readyState == 4) {
        if (req.status == 200) {
          window.console.log("Watering was successful");
        } else {
          window.console.log("Watering was unsuccessful");
        }
      }
    });
    req.send();
  }
In total, the complete Dart code is about 110 lines long, not counting comments and closing braces.

You might wonder why I chose to use Dart so soon after its release, especially since I wasn't even on the Dart team at the time. I've always gotten a kick out of coding in new languages. At the time, I figured that as long as I could talk to the DOM and make XMLHttpRequests, I could do almost anything. These days, Dart is a lot more useful thanks to the growing selection of pub packages available, but even before these things existed, Dart had enough functionality to help water a lawn ;)

If you want to download the complete source code for Irrduino, you can get it from bit.ly/waterjoeslawn.

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