Pin 5 is the control voltage pin of the NE555 timer chip, which is called " Control voltage pin " Or " Control voltage input pin " . This pin is used to control the threshold voltage of the comparator inside the timer, thus changing the way the timer works.
Specifically, when pin 5 is connected to pin 4 (reset pin), the operating period of the timer can be controlled by changing the voltage on pin 5. By changing the voltage on pin 5, the frequency and duty cycle of the output pulse can be adjusted to achieve different timing functions.
In the use of the NE555 timer chip, the fifth pin is usually connected to the positive power supply or ground through external resistors, capacitors and other components to control the length of the timing period and the width of the output pulse. By changing the voltage on pin 5, these parameters can be adjusted to achieve different timing requirements.
Pin 5 of NE555 is the control voltage terminal. When no external control voltage is required, ground through the capacitor.