555 Timer Astable 440 Hz Audio Tone (A4 Note)
Calculate the 555 astable circuit values to generate a 440 Hz tone corresponding to the musical note A4.
How to use this tool
- Enter r1, r2 and capacitance (c) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your frequency and the full breakdown beneath it.
A 555 astable with R1=1 kΩ, R2=10 kΩ, and C=0.1 µF generates an audio-frequency square wave near the musical pitch used in beeper and alarm circuits.
Frequently asked questions
- Can I get a 50% duty cycle from a 555?
- Not directly in standard astable mode (duty cycle is always >50% because t_H > t_L). Adding a diode across R1 (cathode to DISCH) bypasses R1 during discharge, making t_H ≈ t_L ≈ 0.693 × R2 × C for ≈50% duty.
- What is the minimum value for R1?
- The datasheet recommends at least 1 kΩ to protect the discharge transistor. R1 should not be so small that it short-circuits the chip on discharge.