Arduino based humidity sensor for turning humidifier on/off

Moisture sensor_bb

Arduino setup is based on this tutorial, and my modified version is downloadable from here: DHT_Vout

 Changes I made were:

1) Added relay that operates with arduinos 5v output voltage (spec says operating voltage is 12V, but it works with 5v) and connected Arduino digital out pin 3 to relay input. Take a notice that ground pin from transducer that powers arduino needs to be grounded with relays – wire.

2) Wired 230V ground wire and  blue 0-wire straight to the plug and phase line through the relay, so that it is connected when relay gets a signal from arduino, and not connected when it doesn’t ;)


Cord+plug Bauhaus ~10€

Some kind of project case (good idea to get plastic one):

5V Transducer:


Arduino Uno 20€

Deal Extreme:

Item(s) UnitPrice Qty LineTotalPrice
Arduino 5V Relay Module – Blue + Black -121354 US$ 2.40 1 US$ 2.40
Arduino Compatible DHT22 2302 Digital Temperature Humidity Sensor-138531 US$ 10.90 1 US$ 10.90
Arduino Prototype Shield + Mini Breadboard-118040 US$ 4.99 1 US$ 4.99


Total: ~50€

A couple of pictures of the final circuit: