555 is a very commonly used IC for generating accurate timing pulses. It is an 8pin timer IC and has mainly two modes of operation: monostable and astable. In monostable mode time delay of the pulses can be precisely controlled by an external resistor and a capacitor whereas in astable mode the frequency & duty cycle are controlled by two external resistors and a capacitor. 555 is very commonly used for generating time delays and pulses.
Pin Description:
| Pin No | Function | Name |
| 1 | Ground (0V) | Ground |
| 2 | Voltage below 1/3 Vcc to trigger the pulse | Trigger |
| 3 | Pulsating output | Output |
| 4 | Active low; interrupts the timing interval at Output | Reset |
| 5 | Provides access to the internal voltage divider; default 2/3 Vcc | Control Voltage |
| 6 | The pulse ends when the voltage is greater than Control | Threshold |
| 7 | Open collector output; to discharge the capacitor | Discharge |
| 8 | Supply voltage; 5V (4.5V – 16 V) | Vcc |