The 555 is an industrial standard timer IC, this app calculates about it. FEATURES - Can limit the values of resistors/capacitor to E3/E6/E12/E24 series. - Simple waveform which will be output. - Calculating the frequency and duty cycle from resistors/capacitor. - Reverse calculating the values of resistors/capacitor from frequency and duty cycle. And list up recommended parts. - Supported operation is only Astable. HOW TO USE #1 (1) Please input the values of resistor Ra, Rb and capacitor C. (2) A frequency, duty cycle, and waveform are output. HOW TO USE #2 (1) Please input the frequency and duty cycle. (2) A list of recommended parts (resistor Ra, Rb and capacitor C) is output. (3) Can use one of the list as the input of 'HOW TO USE #1', and can calcurate it again.