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555 Astable (free running)

Schematic for a 555 astable oscillator.
Options table for 555 astable oscillator.

    The 555 Timer, designed by Hans Camenzind, is believed to be the most popular IC ever manufactured. It was designed 50 years ago and is still being being manufactured today. Although there are more capable and higher spec parts now available, its ease of use and low cost still make it a good fit for many applications.

    This solver finds the required values for a free running, or continuous output, oscillator. Use the table above to determine what what is solved for based on what is entered.

    The duty cycle is defined as the percentage of a full period that the output waveform is high. Enter the Duty Cycle as a percent (75% = 75). The Duty cycle must be greater than 50%. Practical values range from 55% to 95%.  A default value of 5% is assumed for the capacitor’s tolerance. If you wish to use another value, enter it as a percentage (10% = 10).

    The 555 produces a square wave output that varies between roughly 0V and Vcc - 1.7V. For a sine wave oscillator, use the Sine and Cosine solver. The following formulas are used in this solver.

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