I'm pretty sure I understand how this needs to be done, but I want to make sure so I don't ruin my Arduino or anything else. I have a 120VAC geared motor that I want to be able to switch on and off using the Arduino. If I understand right, I'll need to use a relay. While relays that can be switched with 5V and less than 40mA and will switch 120VAC+ do exist, I don't have one...I have a relay that can be switched with 12V and will switch 120VAC+. What I believe I can do is use the Arduino and a transistor to switch a separate 12V source which will in turn switch the relay, which will power the motor.Am I understanding this right? The Arduino switches the transistor, allowing the 12V source to switch the relay, which will enable power to the motor. Do I need a special transistor? Right now I have some TN4403's, TN2907's and TN3906. I read that I need a TIP120, I can only assume it's because the ones I have won't handle 12V or something.