Ever try to reuse an LED, only to not know which side is positive or negative? Fear no more! In this instructable, I will give you tips on how to find the polarity of common electronics components.
Step 1: Basics
Before you start deducing your own components polarity, you need to know some basics. You probably know this already, but red is ALWAYS positive and black is ALWAYS negative. the only other basic thing you need to know is that if your component is new, then the positive side ALWAYS has the longer lead, and the negative side ALWAYS has the shorter lead. Now that you know the basics, we can deduce other components.
Step 2: LEDs
You already know that the longer lead is positive and the shorter lead is negative on new LEDs, but what if you are using recycled LEDs? The answer lies within the LED. IF you look closely, there is a small part inside the epoxy case that is slender and has a wire coming out of it. That is the anode, and it is on the positive side. On the other side, There is a larger piece with a small "cup" that the wire goes into. That is the cathode, and it is on the negative side.
Step 3: Resistors
Using reused resistors is easy. All you have to remember is that resistance has no polarity! This means that the resistors don't have a negative or positive side.
Step 4: Capacitors
Capacitors are funny. Some have no polarity while others explode if you put them in the wrong way... The most common type of capacitor is the aluminum electrolytic capacitors (photo 1). They have a white stripe with an arrow indicating the negative side. Another type of capacitor is the ceramic capacitor (photos 2 and 3). These have no polarity at all! The last type of capacitor I have here is the tantalum electrolytic capacitors. They usually have markings on one side that show the positive side.
Step 5: Batteries
If you don't put the battery in correctly, you creation won't work! This is why we always need to know the polarity of batteries. On AA, AAA, C, and D, there is always a raised bump on the positive side (photo 1 and 2). Even if your battery doesn't have markings, you can still tell which side is which (I advise against using batteries without casings). Nine volts are a bit different. They are usually marked, and if they aren't, then I probably wouldn't use them. You can tell the difference between the two terminals by determining which one has metal folded on itself (photos 3 and 4). That one is the negative terminal. Coin batteries are easy. They usually have the markings for the positive side engraved on the top (photo 5).
Step 6: Miscellaneous
Usually if the component is positive-negative sensitive, then it will be marked with the plus and minus sign. This is true for speakers, motors, and all other sorts of stuff you can get. A word of warning: even if it is marked with positive and negative symbols, always look up the proper way to use that component before you use it.
Step 7: Now Do It Yourself!
I hope that you found this helpful and that you can reuse you own electronic components! Note: If you are following instructions on how to make something and the instructions say that you should solder the component a certain way, you should probably heed their advice!