The IC555 chip works as follows:
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The output voltage of the two comparators controls the state of the RS trigger and discharge tube. A voltage is added between the power supply and the ground, and when pin 5 is suspended, the voltage at the in-phase input of the voltage comparator C1 is 2VCC \/3, and the voltage at the invert input of C2 is VCC \/3. If the voltage triggering the input TR is less than VCC \/3, the output of the comparator C2 is 0, so that the RS trigger is set to 1, so that the output OUT=1. If the voltage at the threshold input end TH is greater than 2VCC\/3, and the voltage at the TR end is greater than VCC\/3, the output of C1 is 0 and the output of C2 is 1, and the RS trigger can be set to 0 to make the output low.
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IC555 chip is a medium scale integrated device which combines analog and digital functions. Generally, the one made by bipolar (TTL) process is called 555, and the one made by complementary metal oxide (CMOS) process is called 7555. In addition to the single timer, there are corresponding dual timers 556\/7556. The 555 timer has a wide power supply voltage range, can work in 4.5V~16V, 7555 can work in 3~18V, and the output drive current is about 200mA, so its output can be compatible with TTL, CMOS or analog circuit levels.