Will this transistor/ relay set-up work?

Using Arduino Project Guidance
6

Grumpy_Mike:

  1. How did you calculate the size of the resistor and why is it needed exactly.

The FET gate looks like a discharged capacitor. A resistor of 125R keeps the peak current below the 40mA that it is "safe" to draw from an arduino.

  1. Do I need a reverse bias diode because of how the transistor is wired to the relay?

No you need it because of the back EMF generated by the coil.

and make a 5v regulator for the (+)

You need 12V for the relay, so what is the regulator for?

  1. Ohhh, So no matter what size transistor I have I should always have a 125 Ohm resistor? What Watt?
  2. Never though about that. Would this work? http://www.radioshack.com/product/index.jsp?productId=2036270
  3. I meant to say a 5v regulator for the Arduino since it will be in my car.

Thanks!