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:
By selecting proper values for \(R_1, R_2\) and \(C\), we can determine the frequency and duty cycle of the oscillation:
|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%.
The following calculator presents possible resistor and capacitor values, based on a desired frequency and duty cycle.
Possible set ups: