NE555 Timer IC
The original bipolar 555 timer — an 8-pin IC that generates precise delays or square waves from an external RC network.
Note: The in-app simulator currently models the 555's output as a fixed level and does not yet compute real astable/monostable timing from the RC network — timing behavior described below is accurate to the real chip, not yet to the live simulation.
How this component works
The 555 timer is one of the most widely produced integrated circuits ever made. Internally it contains two comparators, an SR flip-flop, and a discharge transistor, wired around a resistor-divider reference. Externally, a resistor-capacitor (RC) network sets the timing.
In astable mode, the 555 free-runs, continuously charging and discharging the timing capacitor to produce a square wave — used for blinking LEDs, tone generation, and clock signals. In monostable mode, it produces a single, fixed-length pulse when triggered — used for debounce circuits and one-shot delays.
The output frequency (astable) or delay (monostable) is set entirely by the external RC values, which is why the 555 is taught as a foundational timing IC before students move to microcontroller-based timing.
Common Use Cases
- Astable oscillator generating a square wave for an LED blinker or tone
- Monostable one-shot for switch debounce or a fixed-length trigger pulse
- PWM-style motor speed control using duty-cycle-adjustable astable wiring
Frequently Asked Questions
How do I set the output frequency in astable mode?
Frequency depends on two resistors and a capacitor: f ≈ 1.44 / ((R1 + 2×R2) × C). Swapping in a larger capacitor or resistor slows the oscillation; smaller values speed it up.
What's the difference between the NE555 and a CMOS 555 (like the TLC555)?
The original NE555 is bipolar — higher output current but more supply current draw and a higher minimum voltage. CMOS versions run on lower voltage and draw far less current, at the cost of lower output drive.