[*]Output: Pin 3 is the output pin. The output is either low, which is very close to 0 V, or high, which is close to the supply voltage that’s placed on pin 8. The exact shape of the output — that is, how long it’s high and how long it’s low, depends on the connections to the remaining five pins.
[*]Trigger: Pin 2 is the trigger, which works like a starter’s pistol to start the 555 timer running. The trigger is an active low trigger, which means that the timer starts when voltage on pin 2 drops to below one-third of the supply voltage. When the 555 is triggered via pin 2, the output on pin 3 goes high.
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