The popular Timer IC 555 is extensively used in short duration timing applications. IC 555 is a highly stable integrated circuit functioning as an accurate time delay generator and free running multi vibrator. But one of the serious problem in 555 timer design is the false triggering of the circuit at power on or when voltage changes. The article describes how IC555 is designed perfectly to avoid false triggering. 555 IC pin functions Pin1 Ground Pin2 Trigger Pin3 Output Pin 4 Reset Pin 5 Control voltage Pin 6 Threshold Pin 7 Discharge Pin 8 Vcc Functional aspects of pins Trigger Pin 2 Usually pin2 of the IC is held high by a pull up resistor connected to Vcc. When a negative going pulse is applied to pin 2, the potential at pin 2 falls below 1/3 Vcc and the flip-flop switches on. This starts the timing cycle using the resistor and capacitor connected to pins 6 and 7. Reset pin 4 Reset pin 4 can be controlled to reset the timing cycle. If pin 4 is grounded, IC will ...
