555 Timer IC Calculator

555 pinout
555 Timer IC
LM555 / NE555 / SA555

PDF Datasheet

This calculator evaluates the performance of the generic bipolar 555 timer chip in both monostable and astable modes. Please enter the component values in the spaces provided, then click 'calculate' and the results will be displayed.

As a rule of thumb, it is best to choose resistor values above 1K and below 1Meg. Large electrolytics should be avoided in favour of large value R's to reduce power consumption and timing inaccuracies due to leakage.

555 Monostable monequation.gif (432 bytes)


T Output High (Seconds) =

555 Astable astequation.gif (1551 bytes)


T1 Output High (Seconds) =
T2 Output Low (Seconds) =
T Total Period (Seconds) =
Frequency (Hz) =
Duty (%High) =

Note: It is not possible to have the low period longer than the high period with this basic circuit. Fortunately the 555 is able to sink as well as source current, or alternatively a PNP output transistor may used to give the necessary inversion.