The LM555 is a highly stable device for generating accurate time delays or oscillations. Additional terminals are provided for triggering or resetting if desired.
It has two main operation modes:
- Time delay mode, or monostable operation - the delay is precisely set using one external resistor and capacitor.
- Oscillator mode, or astable operation - the free running frequency and duty cycle are accurately controlled by two external resistors and one capacitor.
Pin Functions
| Pin | I/O | Description | |
|---|---|---|---|
| No | Name | ||
| 5 | Control Voltage | I | Controls the threshold and trigger levels, determines the pulse width of the output waveform |
| 7 | Discharge | I | Discharges a capacitor between intervals, toggles the output from high to low when voltages reaches 2/3 of the supply voltage |
| 1 | GND | O | Ground Voltage |
| 3 | Output | O | Output driven waveform |
| 4 | Reset | I | Negative pulse applied on the pin to disable or reset the timer |
| 6 | Threshold | I | Compares the voltage applied to the terminal to the 2/3 value of the supply voltage, and determines the set state of the internal flip-flop |
| 2 | Trigger | I | Triggers the internal flip-flop transition from set to reset |
| 8 | VCC | I | Supply voltage relative to ground |
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