I knocked up a rough schematic of what you need. It is by no means complete (I'm meant to be working at the moment). You will need to ground the 12V supply with the arduino ground, calculate the IREF resistor value and add a couple of caps to smooth things out. You could also power the arduino from the 12V supply either by adding a 5V voltage regulator connected to Vin on the arduino OR fit a suitable plug to connect to the arduino power socket.
Thanks, I'm glad there are people that can help me with this.
Again a few questions:
1. Does the 5V output always need to be connected with the digital pin?
2. The resistor on IREF determines the output in mA on the output? And does the GND also need to be connected to the Arduino?
3. Where will the capacitators go and what is there exact function (type)?
This is one of my first projects and I am familiar with most parts but not really about there function and position.
I'm reading a lot of info on the internet, and I just found some tutorials I'm going to read when I have the time.