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Holy Hathaway

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  1. How is the current generated? The current is generated because of the positive and negative charges. The electrons are inside the metal conductor and actually flow from the negative electrode to the positive electrode. It can be imagined that there is a positive charge on the positive side of the power supply. Inside the metal conductor, the nucleus has little force on the electrons, and the electrons are easily separated from the nucleus. So the electrons in the metal conductor close to the positive electrode of the power source are first attracted by the positive charge of the positive electrode of the power source. In the past, the metal conductor that is close to the positive pole of the power supply loses electrons, and it becomes a positive charge itself. The free electrons of the metal conductor that follows it are attracted by this positive charge, and thus the current is formed. If the nucleus of a certain metal has a strong attraction to electrons, then the electrons move hard, which can be understood as "resistance is large". If the nucleus has a weak attraction to electrons, then the electrons move easily. Kind of situation can be understood as "small resistance" In fact, when the free electrons move in a direction, they will collide with the atoms on the crystal lattice. According to the classical conductivity theory of metal, the free electrons collide with the positive ions on the lattice, and the electron motion is hindered to generate resistance. The collision frequency is about 1015 times per second. In the microcosm, it is not advisable to understand with simple particles. In the atomic model, electrons outside the core are distributed according to certain rules. According to the principle of uncertainty, it is impossible to judge the position of the electron at the moment. Only the region where the electron is distributed has a probability distribution. The distribution map of the electron is called an electron cloud. The state of the electron can only be known through the electronic cloud. When an atom is excited by the outside world, the electrons will break away from the control of the nucleus and become free electrons. But the electrons will soon release the excited energy and then return to the electron cloud. Because the number of atoms in a conductor is a huge astronomical number, and the atom is in a state of being excited by heat, statistically, because the number of atoms in the conductor is huge, the number of free electrons is of course huge, so that the whole The conductor looks like a sponge filled with free electrons. From the perspective of energy, the electrons in the electron cloud are controlled by the nucleus, as if they are locked into a dense space. While the energy of free electrons is relatively high, it can move relatively freely. The energy relationship of the former can be called the forbidden band, and the latter is called the conduction band. The electrons move and return between the forbidden band and the conduction band. The function of the power supply is to establish an electric field that acts on the free electrons that satisfy the condition, causing it to move in an directional motion. Electrons are accompanied by excitation and return during motion, which is part of the resistance. Therefore, electrons can't actually be compared with ordinary physical particles. The two are actually different. Of course, you can understand it simply by particle model. The excitation of an atom involves the thermal motion of the atom, so the amount of free electrons is naturally closely related to the temperature of the material, as the resistivity increases with temperature. More articles about resistance and current, visit: Kynix semiconductor electronic blog
  2. The 555 timer is a medium-sized integrated circuit developed by Signetics in 1972 to replace mechanical timers. It is named after the input is designed with three 5kΩ resistors. This circuit later became popular in the world. At present, there are four popular products: two BJTs: 555, 556 (with two 555); two CMOS: 7555, 7556 (containing two 7555). The 555 Timer is a mid-scale integrated device that combines analog and digital functions. It is called 555, which is usually fabricated by bipolar (TTL) process. It is called 7555 by complementary metal oxide (CMOS) process. In addition to single timer, there is corresponding double timer 556/7556. Its power supply voltage range is wide and can operate from 4.5V to 16V, the 7555 can operate from 3 to 18V, and the output drive current is approximately 200mA, so its output is compatible with TTL, CMOS or analog circuit levels. The 555 chip is an extremely versatile chip with up to hundreds of different applications including time-base timing or switching and voltage controlled oscillators and regulators. For those who have been exposed to digital or analog circuits, the 555 chip is definitely a classic. With its low cost and reliable performance, it is widely used in various electrical appliances, including instrumentation, household appliances, electric toys, and automatic control. Its various pin functions are as follows: Pin 1: external power supply negative terminal VSS or ground, under normal grounding. Pin 2: Low trigger terminal TL, this pin voltage is valid when it is less than 1/3 VCC. Pin 3: output OUT. Pin 4: directly clear the terminal RST. When this terminal is connected to a low level, the time base circuit does not work. At this time, regardless of the level of TL and TH, the time base circuit output is “0”, and the terminal should be connected to a high level during normal operation. Pin 5: CO is the control voltage terminal. If the pin is externally connected, the reference voltage of the two internal comparators can be changed. When the pin is not used, the pin should be grounded into a 0.01μF (103) ceramic capacitor to prevent high frequency interference. Pin 6: High trigger terminal TH, this pin is valid when the voltage is greater than 2/3 VCC. Pin 7: discharge end. This terminal is connected to the collector of the discharge tube T and serves as a discharge pin for the capacitor at the time of the timer. Pin 8: external power supply VCC, bipolar time base circuit VCC range is 4.5 -16V, CMOS type time base circuit VCC range is 3-18V, generally 5V.
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