diff --git a/lib/humidity/index.js b/lib/humidity/index.js
index 7100686..cee0781 100644
--- a/lib/humidity/index.js
+++ b/lib/humidity/index.js
@@ -18,7 +18,14 @@
 'use strict';
 
 var console = require('console');
-var Sensor = require('./simulator');
+
+var NTU21D = null;
+try {
+  NTU21D = require('htu21d-i2c');
+} catch (err){
+  console.log(err);
+}
+var Simulator = require('./simulator');
 
 /**
  * Class inspired by W3C's generic-sensor
@@ -26,18 +33,16 @@ var Sensor = require('./simulator');
  **/
 function Humidity(options) {
   var self = this;
+  this.state = 'idle';
   this.type = 'humidity';
-  this.properties = ['level'];
-  for (var property in self.properties) {
-    property = this.properties[property];
-    self[property] = null;
-  }
+  this.level = 100;
   this.onerror = function (err) {
     throw new Error(err)
   }
   this.options = options || {};
   this.options.frequency = this.options.frequency || 1;
-  
+  this.options.controller = this.options.controller || 'simulator';
+
   return this;
 }
 
@@ -45,15 +50,12 @@ Humidity.prototype.update = function update() {
   var self = this;
   try {
     self.hasReading = false;
-    self.sensor.read(function(err, data) {
+    self.sensor.readHumidity(function(err, data) {
       if (err || data === null || typeof data === 'undefined') {
         return self.onerror(data);
       }
       self.timestamp = new Date();
-      for (var property in self.properties) {
-        property = self.properties[property];
-        self[property] = data[property]
-      }
+      self.level = data;
       self.hasReading = true;
       if (self.onreading) {
         self.onreading();
@@ -75,7 +77,16 @@ Humidity.prototype.start = function start() {
   this.state = 'activating';
   if (!this.sensor) {
     try {
-      this.sensor = new Sensor();
+      if (this.options.controller === 'simulator') {
+        this.sensor = new Simulator();
+      } else if ((this.options.controller === 'htu21d') ||
+                 (this.options.controller === 'node-htu21d') ||
+                 (this.options.controller === 'htu21d-i2c')
+                ) {
+        this.sensor = new NTU21D(this.options.sensor);
+      } else {
+        throw new Error("TODO: unsupported controller:" + this.options.controller);
+      }
     } catch (err) {
       if (this.onerror) {
         return this.onerror(err)
@@ -101,7 +112,10 @@ module.exports = Humidity;
 
 
 if (module.parent === null) {
-  var sensor = new Humidity();
+  var config = process.argv[2]
+      ? JSON.parse(process.argv[2])
+      : null;
+  var sensor = new Humidity(config);
   sensor.onreading = function() {
     console.log('log: level=' + this.level);
     this.stop();
diff --git a/lib/humidity/simulator.js b/lib/humidity/simulator.js
index 2a6f878..761a200 100644
--- a/lib/humidity/simulator.js
+++ b/lib/humidity/simulator.js
@@ -19,21 +19,19 @@
 var console = require('console');
 
 function Simulator () {
-  this.value = {
-    level: 100.
-  };
+  this.level = 100.;
 }
 
-Simulator.prototype.read = function (callback) {
-  this.value.level = Math.random();
-  if (callback) return callback(null, this.value);
+Simulator.prototype.readHumidity = function (callback) {
+  this.level = Math.random();
+  if (callback) return callback(null, this.level);
 };
 
 module.exports = Simulator;
 
 if (module.parent === null) {
   var sensor = new Simulator();
-  sensor.read(function (err, value) {
+  sensor.readHumidity(function (err, value) {
     if (err) {
       console.error('error: ' + err);
       throw err;