recently, i have been working on a project magnetic levitation to learn how to apply PID controller to levitate a magnet under a electromagnet. as a mechanical engineer, i have very little idea about arduino and circuit (we did learn some basic skills in engr 97 and ece 83), so as the project proceed, there is a problem come up that i can not solve. i use a hall effect sensor to measure the magnetic field that generated by electromagnet and find out that magnetic field is oscillating. it is very important for this project to have a stable magnetic field so i try to use a voltage regulator, but it doesn’t work well. then my friend told me that i can post my problem in Arduino website, there will be people telling me how to solve the problem. so i post my problem in a forum, and waiting for feedback. surprisingly, there are some many people giving me advises. their advises are just to tell you the way to solve it, but also guide you to look into my circuit, and help me to understand what i really need. people there are so many nice, i am getting much more feedback than i have expected, so it is a very good website to ask for help if you have some problem with circuits and using arduino.