Single Precision Timer NE555 Astable Circuit Calculator

The 555 timer is capable of being used in astable and monostable circuits. In an astable circuit, the output voltage alternates between VCC and 0 volts on a continual basis.

By selecting values for C, R1 and R2 we can determine the period/frequency and the duty cycle.

The period is the length of time it takes for the on/off cyle to repeat itself, whilst the duty cycle is the percentage of time the output is on. ie. T1/T.

In this type of circuit, the duty cycle can never be 50% or lower.

  • Increasing C1 will increase the cycle time (and reduce the frequency).
  • Increasing R1 will increase Time High (T1), but will leave Time Low (T0) unaffected.
  • Increasing R2 will increase Time High (T1), increase Time Low (T0) and decrease the duty cycle (down to a minimum of 50%)


Capacitor (C1):
Resistance 1 (R1):
Resistance 2 (R2):


Frequency =
Period (T) =
Duty Cycle =
Time High (T1) =
Time Low (T0) =

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