555 Timer Calculator
The chip from 1972 that still blinks half the LEDs on Earth. Set your resistors and capacitor, read the beat.
Astable: the blinker
In astable mode the 555 charges C through R1 and R2, discharges it through R2 alone, and flips its output each way. Frequency is 1.44 ÷ ((R1 + 2×R2) × C), and because charge and discharge take different paths, the duty cycle is always above 50%. Want close to an even blink? Make R2 much larger than R1.
Monostable: the one-shot
Ground the trigger pin for a moment and the output goes high for exactly 1.1 × R × C seconds, then drops. That's a debounced button, a staircase light, a "hold for three seconds" behavior, all from one chip, one resistor and one capacitor.
The pin labels on the diagram follow the standard DIP-8, pin 1 at the notch. A fuller version lives on the 555 pinout page.