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In this 555 timer Astable calculator, enter the values of timing capacitor C and timing resistors R1 & R2 to calculate the frequency, period and duty cycle. Here the time period is the total time it takes to complete one on/off cycle (T1+T2), while Duty cycle is the percentage of total time for which the output is HIGH. 555 timer frequency calculator.

555 Timer Astable Calculator

555 Timer Astable Calculator



Duty Cycle:

Time High:

Time Low:

  • TIPS:
  • Period(T) and Frequency(F) are inversely proportional
  • Increase in C1 will decrease Frequency (F)
  • Increase in R1 will increase High Time (T1) but will not alter low Time (T2)
  • Increase in R2 will increase High Time (T1) and also increase low Time (T2)
  • So, always set T2 first and then T1
  • Increase in R2 will decrease duty cycle
  • Once we have all these details, we can get to know the complete properties of the output wave. To get used to the formulas lets calculate the value for parameters using these formulas for the circuit diagram given above.

Model Calculation 555 ic time calculator:
In our circuit diagram the value of Resistors R1 and R2 is 1K and 100K respectively, the value of capacitor C1 is 10uf.

So, R1 = 1K; R2 = 100K and 10uF

Or can be written as R1=1000 Ohms; R2=100000 Ohms, C1=0.00001 Farads

The Time high (T1) is the amount of time during which the pulse stays high (5V) in the output wave. This can be calculated as

Time high (T1) = 0.693 × (R1+R2) × C1

                            = 0.693 × (1000 +100000) × 0.00001

                            = 0.699 seconds

                     T1 = 699 milliseconds

The Time low (T2) is the amount of time during which the pulse stays low(0v) in the output wave. It can be calculated as

Time low (T2) = 0.693 × R2 × C1

                            = 0.693 × 100000 × 0.00001

                            = 0.693 seconds

                     T2 = 693 milliseconds

The time Period (T) is the sum of Time low and Time high. Changing wither Time high or time low will affect the Total time period T

Time Period (T) = 0.693 × (R1+2×R2) × C1 or (T1+T2)

                            = 0.693 × (1000 +2×100000) × 0.00001   or   (0.699+0.693)

                       T = 1.393 seconds

As we all know frequency is just the inverse of time. There are certain applications like a servo motor control where the pulse has to be in a certain frequency for the driver circuit to respond. The frequency can be calculated as

Frequency (F) = 1.44 / (R1+2×R2) × C1 or (1/T)

                            = 1.44 / (1000 +2×100000) × 0.00001   or (1/1.393)  

                        F = 0.718 Hertz

Duty Cycle is always given in terms of percentage, if high time is equal to low time then the pulse has 50% duty cycle and if the off time is zero then it has 100% duty cycle. We can calculate the duty cycle as. 555 timer calculator.

Duty Cycle = (T1/T) × 100

                            = (0.966/1.393) × 100

                     DC = 50.249 %

Electrical Learner we can calculate these parameters for any value of Resistor and Capacitor. Using the 555 timer calculator will really come in handy when you are designing a new circuit for your project. 555 timer frequency and duty cycle calculator.