The NE555 is a highly popular and versatile precision timer IC, first introduced in 1971 by Signetics and now manufactured by many companies including Texas Instruments and Philips . It contains 25 transistors, 15 resistors, and 2 diodes, making it a fundamental building block in electronics for timing, pulse generation, and oscillator applications .
| Pin | Name | Description |
|---|---|---|
| 1 | GND | Ground (0V reference) |
| 2 | TRIG | Trigger: Negative pulse below 1/3 VCC starts timing cycle (output goes HIGH) |
| 3 | OUT | Output: Can sink/source up to 200mA |
| 4 | RESET | Reset: Active LOW; overrides all inputs, resets timing, output goes LOW |
| 5 | CONT | Control Voltage: Adjusts internal reference levels (default 2/3 VCC); bypass with 10nF capacitor to ground if unused |
| 6 | THRES | Threshold: Ends timing when voltage exceeds 2/3 VCC (output goes LOW) |
| 7 | DISCH | Discharge: Open collector output; discharges timing capacitor when output LOW |
| 8 | VCC | Positive Supply: 4.5V to 15V DC |
+Three Operational Modes Astable (oscillation), Monostable (oneshot pulse), Bistable (flip-flop)
+200mA Output Drive - Can directly drive loads without external transistors
+Adjustable Duty Cycle - In astable mode, duty cycle and frequency controlled by external resistors/capacitors
+Wide Voltage Range - Operates from 4.5V to 15V
+TTL/CMOS Compatible - Output levels compatible with 5V logic
√ Available in 8-pin DIP, SOIC, and TSSOP packages
√ Dual version (556) and quad version (558) also available for multiple timers in one package
√ Easy to use with simple external resistor/capacitor networks
