Robert Eisele
Engineer, Systems Architect and DBA

NE555 Astable Circuit Calculator

In astable mode, the NE555 can be used to create an oscillating output between VCC and 0V. All that is needed is a setup like in the following schematic:

NE555 Astable Circuit Schematic

Capacitor \((C)\):
Resistor \((R_1)\):
Resistor \((R_2)\):

By selecting proper values for \(R_1, R_2\) and \(C\), we can determine the frequency and duty cycle of the oscillation:

Period \((T)\):
Duty Cycle:
Time High \((T_1)\):
Time Low \((T_0)\):

A period is the time for one full on/off cycle to repeat itself and the duty cycle is the percentage of time the signal was high in one period. In a NE555 astable circuit, the duty cycle can never be below 50%.

NE555 Period description

Reverse Calculator

The following calculator presents possible resistor and capacitor values, based on a desired frequency and duty cycle.

Frequency \((F)\): Hz
Duty Cycle: %

Possible set ups: