How to make ic 555 timer based PWM signal generator.


PMW(pulse width modulation) is an important feature of today's microcontroller. Using PWM we can effectively control motor, led or any other load. In this project, we generate a PWM signal without any microcontroller. Instead of any microcontroller, we use 555 timer ic.

Parts list
  • 555 timer ic___(01)
  • LED___(01)
  • 9V battry___(01)
  • 0.01uF capacitor___(01)
  • 1K Resistor___(01)
  • 10K Resistor___(01)
  • 100K Pot(variable resistor)___(01)

What is PWM.

PWM is a square wave with logic1(+5V) and logic0(0V) with a different time duration in each logic level which is called as a duty cycle.

The duty cycle of the PWM signal.

As shown is image duty cycle is a percentage of time in with amplitude of signal goes high. The signal gives the highest voltage on 100% duty cycle and gives 0V at 0% duty cycle.

                                        Turn ON time
Duty cycle   =   ----------------------------------------
                           (Turn ON time+Turn OFF time)

The frequency of PWM signal for this circuit is given by below formula which is mention in ic's Datasheet.
t1 = 0.693 (R3 + R1)C
t2 = 0.693 (R1)C 
T = t1+t2
          1                  1.44
f  =  -----  =   ------------------
          T           ( R3 + 2R1)C
















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