555 Timer Calculator
Calculate frequency, period, and duty cycle for 555 timer astable mode.
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Enter the resistance values for R1 and R2 in ohms, and the capacitance in farads. The calculator instantly shows the output frequency, period, duty cycle, and the time the output spends high and low during each cycle. Use scientific notation for small capacitor values (e.g., 1e-6 for 1 microfarad). The results update live as you adjust any value. Use the Copy button to grab the results or Share to send a pre-filled link.
About 555 Timer
The 555 timer IC is one of the most versatile and widely used integrated circuits in electronics. In astable (free-running) mode, it generates a continuous square wave output. The frequency depends on two resistors (R1 and R2) and one capacitor (C). The formula f = 1.44 / ((R1 + 2R2) x C) gives the oscillation frequency. The duty cycle is always above 50% in standard astable configuration because the capacitor charges through both R1 and R2 but discharges only through R2.
Frequently Asked Questions
What is a 555 timer astable mode?
In astable mode, the 555 timer continuously oscillates between high and low states, producing a square wave output without any external trigger. The frequency and duty cycle depend on the resistor and capacitor values.
How do R1 and R2 affect the duty cycle?
The duty cycle equals (R1 + R2) / (R1 + 2R2). To approach 50% duty cycle, make R2 much larger than R1. A perfectly symmetric square wave requires additional circuitry.
What capacitor values are typical for a 555 timer?
Common values range from 1 nF to 100 uF. Smaller capacitors produce higher frequencies while larger ones produce lower frequencies. Electrolytic capacitors work for low-frequency applications.