As I told you at the beginning, you can find these elements in almost any circuit. They are useful devices whenever you work in sinusoidal regime ( AC ). Some of the functions that a capacitor can fulfill in a circuit are:
Adaptation between circuits.
Stabilization of tension. etc.
There are many different types of capacitors. Depending on their capacitance, the voltage they support and the material with which they were built. When making a DIY project, you should not look so much at the material they are made of but at the value of capacitance and the maximum voltage they can withstand (Y type capacitors).
In case you are going to apply positive and negative voltages to the capacitor, you have to look at the type of capacitor. Some of them (the electrolyte) are polarized. This means that the positive voltage must always reach the same pin . Otherwise, you run the risk of destroying the capacitor (in some cases, exploding).
Having said that, here is a list of the most common types:
From Mica : Not polarized. Especially useful for high frequencies and voltages.
Electrolytic : Polarized. With very high capacitance values.
Tantalum : Polarized. It is a type of electrolytic capacitor with greater accuracy and lower capacity / volume ratio.
Plastics : Not polarized. Their values differ depending on the type of plastic used (polyester, polycarbonate, polypropylene, polystyrene …).
Ceramic : Not polarized. Useful at a very wide range of frequencies.
Variables : One of the metal plates is mobile, which is achieved by varying the capacitive capacitor value.
Varicap : Being really a diode, this element is often used as a variable capacitor.
Although most of the capacitors that you can see in the list are unpolarized, if I had to say which is the most common, I would opt for the electrolytic capacitor. It is the one I see most frequently on current PCB boards.
How to Recognize the Value of a Condenser?
In some capacitors (such as electrolytes) you can clearly see their capacitance value. Others use color codes and / or numbers (in the same way as resistors), for example, a capacitor 104 (which is one of the most common).
In case the capacitor you are going to use is of the second type, here is a link in which they will explain how to recognize the value of each of the modalities. In case it seems too messy I leave you another link with a capacitance calculator (Y type capacitors).
Which one should I use and how?
Depending on the project you are doing you will have to use one or the other, so answering this question is very complicated. Even so, here are some clues:
Make sure to use a ceramic capacitor (or at least not polarized) if you are going to have positive and negative voltages on both pins.
Check that the capacitor you are using supports the voltage that arrives (ideally, leave some room for the capacitor to work more relaxed).
If you are going to use it as a complement to another device (for example as a coupling or decoupling capacitor of a LM317 voltage regulator or as a start capacitor) you can see which one you need and how to use it in the device’s Datasheet.
If you want your circuit to only pass alternating current, place a high capacitance capacitor in series. If, on the other hand, you want only the direct current to pass, place capacitors in parallel to ground (GND). This is called a filter (I explain it more carefully at one of the following points).
How to obtain the desired Faradios?
As with the resistors, there are certain commercial values for the capacitors . In case there is none sufficiently close to the value that you need, you can put two or more capacitors in series or parallel to achieve this value (remember to take into account the maximum working ranges of all of them). They are added as follows:
Parallel capacitors : You add directly the capacitance values (the farad) of the capacitors.
Capacitors in series : Calculate the inverse of each capacitor (dividing 1 between the farad of each capacitor), the sums and you do the inverse to that value again.
A filter is a circuit that allows the passage of a set of frequencies, attenuating the rest . Its use is fundamental in many applications. For example, when you tune the radio, what you are doing is changing the capacitance of a variable capacitor (in modern radios Varicaps are used, whose capacitance can be altered electrically), with which you modify the frequencies that pass, allowing you to listen one station or another.