Table of Contents
Introduction
The NE555 is a highly popular and versatile integrated circuit (IC) used as a timer, oscillator, and flip-flop in various electronic applications. Invented in 1972 by Hans R. Camenzind for Signetics, it has since become a staple in both hobbyist and professional electronics projects due to its reliability, simplicity, and low cost.
The NE555 operates in three primary modes:
- Monostable mode: Produces a single output pulse of a precise duration after being triggered.
- Astable mode: Functions as an oscillator, generating a continuous square wave.
- Bistable mode: Acts as a flip-flop with two stable states controlled by external signals.
With just a few external components (resistors and capacitors), the NE555 can achieve functions like delay timing, pulse generation, waveform creation, and frequency modulation. It works over a wide range of voltages (4.5V to 15V) and can drive loads up to 200mA, making it suitable for applications like LED flashers, tone generators, motor speed controllers, and more.
Pinout of NE555
| Pin Number | Pin Name & Description |
|---|---|
| 1 | GND – Ground connection (0V). |
| 2 | TRIG – Trigger input; starts the timing cycle when voltage drops below 1/3 of VCC. |
| 3 | OUT – Output pin; provides high or low signal based on the mode of operation. |
| 4 | RESET – Resets the timing cycle; active low. Connect to VCC if unused. |
| 5 | CV – Control Voltage; adjusts internal thresholds. Typically connected to GND via a 10nF capacitor. |
| 6 | THR – Threshold input; ends the timing cycle when voltage exceeds 2/3 of VCC. |
| 7 | DISCH – Discharge pin; used to discharge the external capacitor. |
| 8 | VCC – Positive power supply (4.5V to 15V). |
Key Features
- Operating Voltage: 4.5V to 15V (some variants work up to 18V).
- Output Current: Up to 200mA.
- Operating Modes:
- Monostable Mode: Generates a single pulse of a specific duration when triggered.
- Astable Mode: Operates as an oscillator, generating a continuous square wave.
- Bistable Mode: Functions as a flip-flop with two stable states.
- Adjustable Frequency and Duty Cycle: Configurable using external resistors and capacitors.
Applications
- Timers: Delaying or timing events.
- Oscillators: Generating square waves or PWM signals.
- Pulse Width Modulators: Used in motor control and signal processing.
- Tone Generators: For audio and alarms.
- LED/Lamp Flashers: Flashing lights for indicators or decorative purposes.
