Since a potentiometer is used for resistor, we can output square wave signals with different duty cycles by adjusting its resistance. Then the capacitor is recharged and the output voltage flips again: Then C1 discharges via R2 till 2/3Vcc, in a time span: When the voltage at C1 reaches the threshold 2/3Vcc, the timer is reset and pin 3 is Low level. The capacitor C1 charges via R1 and R2, in a time span: Upon the energizing, since the voltage at C1 cannot change abruptly, which means pin 2 is Low level initially, set the timer to 1, so pin 3 is High level.

The oscillator starts to shake once the circuit is power on. Connect the RET (pin 4) to GND, CV (pin 5）to another capacitor C2 and then to the ground. In this experiment, apply it under the astable mode, which means it works as an oscillator.Ĭonnect a resistor R1 between the VCC and the discharging pin DS, another resistor between pin DS and the trigger pin TR which is connected to the threshold pin TH and then to the capacitor C1. The NE555 timer works under the monostable, astable and bistable modes. Pin 8 (VCC): positive terminal for the NE555 timer IC, ranging +4.5V to +16V Pin 7 (DISCHARGE): output synchronized with Pin 3, with the same logical level but this pin does not output current, so pin 3 is the real High (or Low) when pin 7 is the virtual High (or Low) connected to the open collector (OC) inside to discharge the capacitor Pin 6 (THRESHOLD): when the voltage at the pin increases to 2/3 VCC (or the threshold defined by the control board), the output terminal sends out a High level Pin 5 (CONTROL VOLTAGE): to control the threshold voltage of the chip (if it skips connection, by default, the threshold voltage is 1/3 VCC and 2/3 VCC) Pin 4 (RESET): when a Low level is received at the pin, the timer will be reset and the output will return to Low level usually connected to positive pole or neglected Pin 3 (OUTPUT): outputs High or Low, two states 0 and 1 decided by the input electrical level maximum output current approx. Pin 2 (TRIGGER ): when the voltage at the pin reduces to 1/3 of the VCC (or the threshold defined by the control board), the output terminal sends out a High level

The 555 is a complex hybrid circuit with dozens of components such as a divider, comparator, basic R-S trigger, discharge tube, and buffer. It is now widely used in various electronic products because of its reliability, convenience, and low price. The 555 IC was originally used as a timer, hence the name 555 time base circuit.

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