Hi,
I would like to send humidity sensor data wirelessly via an RF link to an Arduino that is connected to my PC.
Humidity sensor:
RF transm/receiver:
Can I connect the sensor directly to the transmitter and have the Arduino on the receiver end use its sensor library to interpret the data? Or do I have to use 2 Arduino's?
Thanks in advance.
Can I connect the sensor directly to the transmitter
No.
That was a helpful answer Groove 
I will be of a little more help. If you need more help, just ask.
You need 2 Arduino's, 1 sensor and 2 RF transceivers.
Arduino 1 (humidity sensor side):
Connect the sensor and 1 transceiver to the Arduino. Program the Arduino in a way that it reads the values coming from the sensor and have then transmit the values by the RF transceiver.
Arduino 2 (pc side)
Wire up the 2nd transceiver to Arduino and have it poll for incoming RF data from Arduino 1. Send the values it received over serial connection to your PC. You will need to have some sort of software to read the values coming from Arduino 2 to the PC. You can do this with the Arduino IDE or write your own code in Visual Studio, or any other programming language of your liking.
Hint: google for VirtualWire and Arduino for the RF link.
how to wire up everything to Arduino's etc... try to find out or ask here.
Many people are willing to help you.
Thanks a lot for your clear explanation, Dutchman!
Do you know what the cheapest solution is for Arduino 1? I mean, it will be enclosed in my cigar humidor just to send the sensor data, and not be used for anything else, so it would be a waste of money to put a full Arduino board in it, won't it? I was thinking of a Freeduino or maybe just the atmega microcontroller but I guess it's a bit too difficult for my current microcontroller skill level 
You can do with only 1 Arduino and an extra Atmega processor. Program the transmitter/sensor part and upload it to the processor. When it works, you can remove the processor and implement it in a schematic like shown in this image: http://farm3.static.flickr.com/2644/4066890569_3e22f27616.jpg and add the rf and sensor part. In my post above, that would be Arduino 1.
After that you write the code for the receiving part. Insert the spare Atmega processor in the socket of this Arduino (Arduino 2) and burn the code.
That would be all.
That would be all.
Well, other than the fact that the "extra Atmega" processor will need to be one with a bootloader already installed; other than that plus the extra parts, that would be the best way to go.
If you are looking for the extra parts, though, an option might be to go for an RBBB:
http://www.moderndevice.com/products/rbbb-kit
You can either go for the kit, or just buy the board and add your own parts. It would save you from having to build your own PCB or solder a stripboard version (though if you have all parts already and the stripboard, and are low on cash - then use what you have or can afford!).
