555 breathing light

Xinjiang Institute of Engineering Electronics Competition First Prize Entry Topic: 555 Breathing Lamp Circuit Principle: 555 timer consists of a voltage divider composed of three resistors with a resistance of 5KΩ, two voltage comparators C1 and C2, a basic RS flip-flop, and a discharge It is composed of transistor TD and buffer inverter G4. Pin 1 is the ground terminal; pin 2 is the low-level trigger terminal, from which the low-level trigger pulse is input; pin 6 is the high-level trigger terminal, from which the high-level trigger is input. Level trigger pulse; pin 4 is the reset terminal, inputting a negative pulse can directly reset the 555 timer; pin 5 is the voltage control terminal, applying voltage to this terminal can change the reference voltage of the comparator. When not in use, the reference voltage of the comparator can be changed by 0.01uf Ceramic capacitor discharges; pin 3 is the output terminal, the output high voltage is slightly lower than the power supply voltage 1V-3V, the output current can reach 200mA, so it can directly drive relays, light-emitting diodes, indicator lights, etc.; pin 8 is the power terminal, which can be Use within the range of 5V to 18V. This circuit consists of the NE555 chip, 2 resistors and 1 capacitor. The capacitor C3 is charged and discharged to generate the switching time length. R1 and R2 charge and discharge capacitor C3. When the circuit is working, C1 is charged through R1 and R2. The voltage of capacitor C1 continues to rise. When the voltage reaches a higher value (usually 2/3 of the power supply voltage), pin 6 of the NE555 connected to it also reaches the same voltage. At this time, the NE555 chip starts to act internally, outputting pin 3 to a low level (that is, 0V), and at the same time, pin 7 is also at a low level (0V). Because pin 7 becomes low, the current from the positive pole of the power supply flows directly into pin 7 through R1. Because the current always flows from the high-level end to the nearest low-level end with the least resistance. The current flows into pin 7, and there is no current flowing through R2 to charge C3. Instead, only C3 discharges to pin 7 through R2. When the voltage on C3 is less than a certain value (usually 1/3 of the power supply voltage), the voltage of pin 2 connected to it is also lower than this value. At this time, the NE555 chip starts to act, causing pin 3 to output high level, and at the same time, pin 7 is no longer low level. Now the circuit is back to the state it was in when it first started working, and C3 is recharged. If the cycle continues like this, the voltage of C3 always hovers between 1/3 and 2/3 of the power supply voltage, but it causes pin 3 of the NE555 chip to output a stable square wave. Adjusting the value of R2 or C2 can adjust the cycle time of the square wave. Pin 3 outputs a stable square wave. When it is high level, C1 is charged first, so that the voltage at both ends of the LED gradually increases, and the LED gradually lights up; when it is low level, C1 discharges, the voltage gradually decreases, and the LED gradually turns off, that is, Realize the effect of LED breathing.