555 Timer LED Flasher - Calculating the Pulse Rate




Pulse Rate

  • In astable mode, the output from the 555 timer is a continuous pulse waveform of a specific frequency that depends on the values of the two resistors (RA and RB) and capacitor (C) used in the circuit. 
 circuit-pulse

Circuit Pulse

  • The charge time (Output High)
    • t1=0.693(R1+R2)C1
  • And Output Low
    • t2=0.693(R2)C1
  • Total time period , T=t1+t2.
  • Frequency , F=1/T.

Duty Cycle Calculation

 Example

Duty Cycle Calculation


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