i have the schematics for a PWM using a 555 Ic and an RC network taken from this forum:
http://forum.allaboutcircuits.com/showthread.php?t=24028

instead of changing the Oscillation time manually with a poti, i need it to steadily change the pulse time, and thought of using another 555 PWM circuit but i dont know how to combine them together .

any thoughts will be appreciated,


thanx

Tom

 

The pot in the circuit changes the duty-cycle of the pulses which is PWM. The pot does not change the frequency.

 

Most good PWM do not change frequency. If you want you could use a standard monostable along with a variable frequency oscillator, or you could use the one I have in chapter 5 (The 555 and PWM) of my article, Figure 5.3

LEDs, 555s, Flashers, and Light Chasers