I needed a way to vary the voltage going to the electromagnet. I immediately thought of using a digital potentiometer. When I bought my first digital potentiometer IC, I realized that it couldn't handle the current needed for the electromagnet. I bought a couple that could handle the current, but they were all made for PCBs, and I had no experience with printing PCBs. Therefore, I needed to find a new way to accomplish this task. I decided to use a transistor and a PWM signal from the Arduino. I tried about 10 different transistors. I finally found one that could handle the current going to electromagnet. It got really hot so I had to use liquid silicon and a heatsink to cool the transistor.