Classic 555 timer IC. Monostable, astable, and bistable modes.
| Pin | Name | Function | Type |
|---|---|---|---|
| 1 | GND | Ground reference | GND |
| 2 | TRIG | Trigger, starts timing on low pulse | I/O |
| 3 | OUT | Output, high or low based on state | I/O |
| 4 | RESET | Active low reset, tie high if unused | I/O |
| 5 | CTRL | Control voltage, sets threshold level | ADC |
| 6 | THR | Threshold, resets output above 2/3 VCC | I/O |
| 7 | DIS | Discharge, connects to timing capacitor | I/O |
| 8 | VCC | Positive supply, 4.5V to 16V | PWR |
The 555 timer is one of the most widely produced ICs in history, originally designed in 1971. It operates in monostable (one-shot timer), astable (free-running oscillator), or bistable (flip-flop) modes. Used in everything from LED blinkers to pulse-width modulation circuits.