@ 555 PWM Generator

This PWM generator with adjustable duty cycle is made with the 555 timer IC. 
The circuit is an astable multivibrator with a 50% pulse duty cycle. 
The difference from the standard design of a 555 timer is the resistance between 
pins 6 and 7 of the IC composed of VR1, VR2, R2, D1 and D2.

The diodes D1 and D2 set a definite charging time for C1 which produces a 50% duty cycle
in a normal case. 
Dedicated duty cycle (n) is dependent on VR1 and VR2 in the following description:

         n [ % ] = 1 + ( VR2 / VR1 )     

If VR2 = 0 (n = 100%) then the frequency can be approximately calculated with the following formula:

          Frequency = 0.69 / ( ( 2 * VR1 + VR2 + 4.7kΩ ) * C1 )

PWM Generator Circuit Diagram

In the capture, the duty cycle is not between 0% and 100% but it is within reasonable range.
Thus used VR1 of 20K, VR2 of 100K and 10nF for C1.

Printed circuit layout of the pulse generator

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Waveform Captures in my Friend's Lab