Enter your 555 timer's Configuration Mode, resistor values (R1, R2), and C1 Capacitance to calculate the output Frequency, Duty Cycle, Period, and the exact Time High (T1) and Time Low (T0) of your PWM signal.
Frequency
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Period
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Duty Cycle
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Time High (T1)
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Time Low (T0)
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Astable mode produces a continuous square wave output, while monostable mode produces a single pulse for each trigger input. Astable is used for oscillators and PWM, monostable for timing delays.
In standard astable configuration, the capacitor charges through R1+R2 but discharges only through R2. Since R1 is always in the charging path, the high time is always longer than the low time, making duty cycles below 50% impossible without circuit modifications.
For astable mode, use the formula f = 1.44/((R1+2×R2)×C). Rearrange to solve for resistance: (R1+2×R2) = 1.44/(f×C). Choose R1 and R2 values that satisfy this equation while considering the desired duty cycle.
Typical values range from 1nF to 1000µF depending on frequency. For audio frequencies (20Hz-20kHz), use 1nF-10µF. For lower frequencies or timing applications, use larger capacitors up to 1000µF.
Calculations are typically accurate within 5-10% for standard conditions. Real-world factors like component tolerances, temperature, supply voltage variations, and load impedance can affect actual performance.
Standard 555 timers can operate up to about 500kHz reliably. For higher frequencies, use CMOS versions like the 7555 which can reach several MHz, or consider other oscillator circuits.