How to control two devices with Arduino?
Connect both of your appliances i.e AC and Humidifier to 2 different relays. Connect the relays to the Arduino Uno digital I/O pin using a small current amplifier circuit or a Darlington Transistor pair that will amplify the current going to the relay.


Relay circuit



Darlington Pair

Now the connection of your sensor with arduino.

In your code you have to use DHT library i.e.

#include &lt;dht11.h&gt;


define your DHT11 object as

dht11 DHT11;    //(class object;)


define your DHT11 sensor pin like this

DHT11.read(dht_output_pin);


You can the similar code to control your relay according to the temperature and humidity here. Simply first check the AC temperature and switch on/off the AC relay and then check the Humidifier humidity and switch on/off the humidifier relay. 

*** Connect your sensor output to the Digital Pin of the Arduino