1. The capacitor connected in parallel between the DC power supply (Vcc) and the ground can be called a filter capacitor. The filter capacitor filters out the clutter and AC components of the power supply, smooths the pulsating DC power, and stores electric energy. The value is generally 100-4700uF. The value is related to the load current and the purity of the power supply. The larger the capacity, the better. Sometimes there is a capacitor with a smaller capacity next to the large capacitor, called a high-frequency decoupling capacitor. It is also a type of filtering used to filter out high-frequency clutter in the power supply to avoid self-excitation in the circuit state and stabilize the working state of the circuit. The value is generally 0.1-10uF. The value is related to the frequency of filtering out clutter.
The function of such connection is generally called "decoupling", also called "back-crossing" and "bypass" capacitors, which are often arranged near the power supply, IC and functional module circuits. It is better to use non-inductive ceramic chips and monolithic capacitors.
The function is to provide a path for high-frequency signals, reduce the internal resistance of the power supply, remove the influence of the "long line" of the power supply and the ground wire on the copper clad board, and prevent the "harmful cross-connection" between the various parts of the public power supply. 10nF is commonly used.
2. On the development board, there are usually many 0.1uF non-electrolytic capacitors and 10uF electrolytic capacitors between the DC power supply and the ground.
The purpose of these capacitors is to make a low impedance between the power line and the ground line, and the power supply is close to an ideal voltage source. You can say that it is filtering, but you need to figure out what wave is being filtered. It is not to filter the ripple of the power supply, but the ripple caused by the current change of a certain chip on the power line, so that it does not affect other chips.
Use 0.1uF non-polar capacitor and 10uF electrolytic capacitor in parallel because the parasitic inductance of electrolytic capacitor is relatively large, and the ability to eliminate high-frequency ripple is poor. The non-polar capacitor has a small parasitic inductance and a better ability to filter high-frequency ripples. However, if the capacity is selected according to the requirements of low frequency, the non-polar capacitor is too large and the cost is high, the electrolytic capacitor is small, and the same capacity is cheaper. Therefore, two types of capacitors are used in parallel.
If you design your own circuit, you should use it in this way, and the location and wiring of each capacitor are very particular.
I can only say two principles:
1) The connecting wires between the two ends of the small-capacity non-polar capacitors and the power pins and ground pins of the chip should be as short as possible, and the shorter the better.
2) The power supply is usually introduced by other circuit boards, and there are usually only one or two electrolytic capacitors on each circuit board. For an electrolytic capacitor, put it where the power supply enters the circuit board. At this time, the electrolytic capacitor is of course far away from the chips, but since the electrolytic capacitor mainly works at a lower frequency, it does not matter if it is a little farther away. If two electrolytic capacitors are used on the circuit board, the other one is placed near the chip that consumes the most power.
These are related to the layout of the circuit board components and the wiring arrangement of the ground wire (multilayer boards usually have a ground layer).
0.1μF capacitor for noise below 10MHz works well.
Press C=1/F, that is, take 0.1μF for 10MHz
Simply put, connect the interference to ground through a capacitor