Preface

This calculator helps design an astable multivibrator from a standard 555 timer IC.

R1 should be 1000 Ohms or more

R2 should be 1000 Ohms or more

Total of R1+R2 should be 3.3 megOhms or less

C1 should be .0005 Microfarads or more

Frequency should be 1.0 MHz or less

Percent High Time is a function of the relationship of R1 and 2*R2. Percent High Time must be greater than 50% and less than 100%.

Multivibrator Design

The following diagram illustrates the basic hookup.

To compute R1, R2 and C1 for a given frequency

1. Enter the desired frequency.
2. Enter any two of R1 (more than 1K Ohms), R2 (more than 1K Ohms) and/or C1 (more than 0.0005 microfarads)
3. Click and leave the field of (R1,R2 and C1) which was computed for you. This will compute the duty cycle fields.

To reverse engineer a timer-based circuit to determine frequency

1. Enter R1, R2 and C1