You simply enter the frequency (or alternatively the delay period) that you want your 555 timer chip to run at - and an initial timing capacitor value - then the 555 Timer Tool calculates a list of the best combinations of other components that meet your requirements.
As a convenience, you can also use touch gestures to snap component values up or down to the next preferred value. To do that just stroke the values displayed on the circuit diagram. Stroke upward to adjust upwards, or stroke down to adjust downwards.
The preferred value range that values are snapped to is selected by choosing "Preferences" from the options menu.
For example, suppose you wanted a 555 timer to oscillate at 440 Hz (the A above middle C on the piano keyboard) then just:
- click the f (frequency) button on the circuit diagram, enter 440 then press the OK button
- click the C1 button on the circuit diagram, enter 47, then press the nF button, then press the OK button.
The 555 Timer Tool calculates combinations close to 440 Hz and updates the values on the circuit diagram with the closest combination.
How do you know to key in 47 nF as the initial value for C1? ...well, you don''t - but you have to start somewhere and 47 nF is middle of the road!