Adding support for the htu21d hygrometer and temperature

eg/hygrometer-htu21d.js

@@ -0,0 +1,16 @@
+var five = require("../lib/johnny-five.js");
+var board = new five.Board();
+
+board.on("ready", function() {
+  var hygrometer = new five.Hygrometer({
+    controller: "HTU21D"
+  });
+
+  hygrometer.on("data", function() {
+    console.log(this.relativeHumidity + " %");
+  });
+});
+
+// @markdown
+// - [HTU21D - Humidity Sensor](https://www.adafruit.com/products/1899)
+// @markdown

eg/temperature-htu21d.js

@@ -0,0 +1,16 @@
+var five = require("../lib/johnny-five.js");
+var board = new five.Board();
+
+board.on("ready", function() {
+  var temperature = new five.Temperature({
+    controller: "HTU21D"
+  });
+
+  temperature.on("data", function() {
+    console.log(this.celsius + "°C", this.fahrenheit + "°F");
+  });
+});
+
+// @markdown
+// - [HTU21D - Humidity Sensor](https://www.adafruit.com/products/1899)
+// @markdown

lib/hygrometer.js

@@ -0,0 +1,96 @@
+var Board = require("../lib/board.js"),
+  Emitter = require("events").EventEmitter,
+  util = require("util");
+
+// References
+//
+var Controllers = {
+  HTU21D: {
+    initialize: {
+      value: function(opts, dataHandler) {
+        var Multi = require("../lib/imu");
+        var driver = Multi.Drivers.get(this.board, "HTU21D", opts);
+        driver.on("data", function(data) {
+          dataHandler(data.humidity);
+        });
+      }
+    },
+    toRelativeHumidity: {
+      value: function(raw) {
+        return (125.0*(raw/65536)) - 6;
+      }
+    }
+  }
+};
+
+var priv = new Map();
+
+function Hygrometer(opts) {
+  var controller, freq, last = 0, raw;
+
+  if (!(this instanceof Hygrometer)) {
+    return new Hygrometer(opts);
+  }
+
+  Board.Component.call(
+    this, opts = Board.Options(opts)
+  );
+
+  freq = opts.freq || 25;
+
+  if (opts.controller && typeof opts.controller === "string") {
+    controller = Controllers[opts.controller.toUpperCase()];
+  } else {
+    controller = opts.controller;
+  }
+
+  if (controller == null) {
+    controller = Controllers["ANALOG"];
+  }
+
+  priv.set(this, {});
+
+  Object.defineProperties(this, controller);
+
+  if (!this.toRelativeHumidity) {
+    this.toRelativeHumidity = opts.toRelativeHumidity || function(x) { return x; };
+  }
+
+  var propDescriptors = {
+    relativeHumidity: {
+      get: function() {
+        return this.toRelativeHumidity(raw);
+      }
+    }
+  };
+  // Convenience aliases
+  propDescriptors.RH = propDescriptors.relativeHumidity;
+
+  Object.defineProperties(this, propDescriptors);
+
+  if (typeof this.initialize === "function") {
+    this.initialize(opts, function(data) {
+      raw = data;
+    });
+  }
+
+  setInterval(function() {
+    if (raw === undefined) {
+      return;
+    }
+
+    var data = {};
+    data.RH = data.relativeHumidity = this.relativeHumidity;
+
+    this.emit("data", null, data);
+
+    if (this.relativeHumidity !== last) {
+      last = this.relativeHumidity;
+      this.emit("change", null, data);
+    }
+  }.bind(this), freq);
+}
+
+util.inherits(Hygrometer, Emitter);
+
+module.exports = Hygrometer;

lib/imu.js

@@ -14,6 +14,64 @@ var priv = new Map();
 var activeDrivers = new Map();
 
 var Drivers = {
+  // Based on the AdaFruit Arduino driver
+  // https://github.com/adafruit/Adafruit_HTU21DF_Library
+  // https://www.adafruit.com/products/1899
+  HTU21D: {
+    ADDRESSES: {
+      value: [0x40]
+    },
+    REGISTER: {
+      value: {
+        TEMPERATURE: 0xE3,
+        HUMIDITY: 0xE5
+      }
+    },
+    initialize: {
+      value: function(board, opts) {
+        var READLENGTH = 3;
+        var io = board.io;
+        var address = opts.address || this.ADDRESSES[0];
+
+        var computed = {
+          temperature: {},
+          humidity: {}
+        };
+
+        var readCycle = function(isTemp) {
+          var register = isTemp ? this.REGISTER.TEMPERATURE : this.REGISTER.HUMIDITY;
+
+          io.i2cReadOnce(address, register, READLENGTH, function(data) {
+            var msb = data[0];
+            var lsb = data[1];
+
+            var value = (msb << 8) | lsb;
+
+            if (isTemp) {
+              computed.temperature = value;
+            } else {
+              computed.humidity = value;
+              this.emit("data", computed);
+            }
+
+            readCycle(!isTemp);
+          }.bind(this));
+        }.bind(this);
+
+        io.i2cConfig(opts);
+
+        // Kick off "read loop"
+        //
+        readCycle(false);
+      }
+    },
+    identifier: {
+      value: function(opts) {
+        var address = opts.address || Drivers["HTU21D"].ADDRESSES.value[0];
+        return "htu-s1d-" + address;
+      }
+    }
+  },
   // Based on the example code from
   // http://playground.arduino.cc/Main/MPU-6050
   // http://www.invensense.com/mems/gyro/mpu6050.html

lib/johnny-five.js

@@ -17,6 +17,7 @@ module.exports = {
   Fn: require("./fn"),
   Gripper: require("./gripper"),
   Gyro: require("./gyro"),
+  Hygrometer: require("./hygrometer"),
   IMU: require("./imu"),
   IR: require("./ir"),
   Keypad: require("./keypad"),
@@ -66,6 +67,7 @@ module.exports.Board.Virtual = function(opts) {
 };
 
 module.exports.Multi = module.exports.IMU;
+module.exports.Humidity = module.exports.Hygrometer;
 
 module.exports.Analog = function(opts) {
   return new module.exports.Sensor(opts);

lib/temperature.js

@@ -287,6 +287,22 @@ var Controllers = {
       }
     }
   },
+  HTU21D: {
+    initialize: {
+      value: function(opts, dataHandler) {
+        var Multi = require("../lib/imu");
+        var driver = Multi.Drivers.get(this.board, "HTU21D", opts);
+        driver.on("data", function(data) {
+          dataHandler(data.temperature);
+        });
+      }
+    },
+    toCelsius: {
+      value: function(raw) {
+        return (175.25*raw/65536)-46.85;
+      }
+    }
+  },
   //http://playground.arduino.cc/Main/MPU-6050
   MPU6050: {
     initialize: {