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:
| 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. Please note that \(R_1\) should not be less than 1k, since the internal discharge transistor of the 555 will try to short the power supply, which may damage it.
| Frequency: | ||
|---|---|---|
| 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%.
Reverse Calculator
The following calculator presents possible resistor and capacitor values, based on a desired frequency and duty cycle.
| Frequency \((F)\): | Hz |
|---|---|
| Duty Cycle: | % |
| Exclude \(R_1 < 1k\): |
Possible set ups: